Computational Insights Into All-Fused Ring Non-Fullerene Acceptors for Enhanced Stability and Performance
Choppella S., Haseena S., Ravva M.K.
Article, Journal of Computational Chemistry, 2026, DOI Link
View abstract ⏷
The chemical stability and performance of non-fullerene acceptors (NFAs) are critical for achieving high power conversion efficiency (PCE) and device stability. This study presents a novel computational design strategy for addressing key stability challenges. The photochemical stability is improved by removing the vinylene bridge between the core and end groups, which often causes degradation and photoisomerization. All-fused non-fullerene acceptors (AFNFAs) are designed by directly fusing high-performance end groups with core units such as Y6 (FY6) and ITIC (FITIC). Density functional theory (DFT) and molecular dynamics simulations show that the new molecules exhibit superior optoelectronic properties and favorable bulk-phase morphologies. The results also show highly ordered packing of acceptor dimers and efficient charge transport. Additionally, the voltage losses associated with exciton diffusion, dissociation, and energetic disorder in electron affinities are minimal. Overall, the proposed AFNFAs with imide end groups emerge as promising candidates for stable high-performance acceptors in organic solar-cell applications.
C–F Bond Functionalization: Controlled Didefluorination of o-Trifluoromethyl Benzylamines
Article, Organic Letters, 2025, DOI Link
View abstract ⏷
Organofluorine compounds are widely used but pose environmental concerns. We report a base-mediated didefluorination of o-trifluoromethyl benzylamines via difluoroquinone methide intermediates, yielding monofluorinated tricyclic 2H-imidazoles. This efficient method showcases a broad substrate scope and offers mechanistic insight through a 1,4-elimination pathway of two fluoride ions.
Conformationally Locked Medium Bandgap Non-Fused Electron Acceptors via Direct C–H Arylation for Efficient Organic Solar Cells Using Non-Halogenated Solvent
Shaik N., Walke A.U., Maricherla H., Syed N., Yadagiri B., Mery S., Singh S.P., Ravva M.K., Sharma G.D., Narayanaswamy K.
Article, ACS Applied Energy Materials, 2025, DOI Link
View abstract ⏷
The development of high-performance, fully non-fused ring electron acceptors (NFREAs) for organic solar cells (OSCs) is often hindered by multistep synthesis, use of hazardous reagents, and high synthetic complexity (SC), ultimately limiting their figure-of-merit (FOM). In this study, we report three simple and cost-effective NFREAs, SN-1, SN-2, and SN-3, featuring a dialkoxybenzene central core and hexyldicyanorhodanine terminal acceptor groups linked via distinct π-bridging units: furan, thiophene, and ethylenedioxythiophene (EDOT), respectively. These NFREAs were synthesized in just four steps using a direct C–H arylation reaction, without any hazardous reagents, with very high overall yields of up to 49%. To enhance the molecular planarity and charge transport, an intramolecular noncovalent interaction strategy was employed to restrict the C–C bond rotation between the π-conjugated units. Notably, SN-3 exhibited multiple O···S and O···H interactions between core and end groups, effectively rigidifying the backbone and promoting J-aggregation. As a result, PM-6:SN-3-based OSCs achieved a power conversion efficiency (PCE) of 11.56%, a high FOM of 67.09, and a low SC value of 17.26. In comparison, devices based on SN-1 and SN-2 delivered PCEs of 10.26% and 6.97%, respectively. These findings underscore the critical role of noncovalent interactions in conformationally stabilizing simple NFREAs and highlight their potential for high FOM OSCs.
Mn-Doped CsPbCl3Nanocrystals with Mucic Acid Surface Passivation for Enhanced Performance in Photoresponsive Devices
Article, ACS Applied Nano Materials, 2025, DOI Link
View abstract ⏷
The metal doping process not only enhances the intrinsic properties of semiconducting perovskite nanocrystals (PNCs), including optoelectronic, magnetic, and electrochemical properties, but also significantly improves their photophysical performance. For instance, Mn doping can enhance the photophysical properties of CsPbCl3PNCs to some extent. In addition to doping, surface passivation is a promising strategy to further improve the photophysical properties and stability of these materials. In this study, we demonstrate that the surface defect states of the Mn-doped CsPbCl3PNCs can be effectively reduced through postsynthesis surface passivation with mucic acid at room temperature, resulting in enhanced photophysical properties and stability. The XRD patterns confirmed the successful doping of Mn into the CsPbCl3lattice. FTIR and XPS measurements verified the successful mucic acid passivation. Notably, the mucic acid-treated Mn–CsPbCl3PNCs exhibited a photoluminescence quantum yield of 55–57%, compared to just 18% for unpassivated Mn–CsPbCl3. The photostability test confirms that passivated PNCs are more stable than those without passivation. The Mn-CPC-MA-3 PNCs showed significantly improved current stability and intensity under visible light illumination with a higher photocurrent density of ∼0.01 μA/cm2versus −0.029 μA/cm2for Mn-CPC PNCs.
Computational insights into tuning TADF properties via multiple donor–acceptor linkages
Jacob J.M., Sandeep B., Kumar K.P., Rajapandian V., Ravva M.K.
Article, Journal of Chemical Sciences, 2025, DOI Link
View abstract ⏷
Traditionally, thermally activated delayed fluorescence (TADF) molecular design has focused on donor–acceptor (D–A) structures. However, this study explores alternate molecular configurations that extend beyond the conventional models. Using density functional theory (DFT) and time-dependent DFT calculations, we systematically investigated the impact of various donor and acceptor arrangements, such as D_A, D_A_D, A_D_A, D_A_D_A, and D_A_A_D, on the TADF properties of emitters using 5,10-dihydrophenazine (DHPZ) as the donor and benzophenone (BP) as the acceptor. In tetrad systems, the electronic structure of TADF emitters strongly depends on the spatial arrangement of the donor and acceptor units. For instance, in the D_A_D_A configuration, the lowest three singlet and triplet states exhibit charge transfer character. In contrast, the D_A_A_D configuration reveals significant Frenkel-type character in T3 and T4 states. The involvement of these higher triplet states enhances the spin–orbit coupling value and improves the reverse intersystem crossing (RISC) rates. Additionally, the configuration of donor and acceptor units influences the number of potential RISC channels. Overall, the D_A_A_D configuration emerges as a promising design, demonstrating superior TADF performance through multiple efficient exciton utilization pathways (up to 10 RISC channels) and faster RISC rates (> 105 to 108 s–1) compared to D_A_D_A.
Single-Atomic Co–N2 O2 Sites to Construct Quinazolinone Scaffolds via Tandem Oxidation
Anbuselvan N., Sivaprakash S., Nithya K., Anakkayath A., Ravva M.K., Rana R.K., Suresh D., Amali A.J.
Article, ACS Applied Nano Materials, 2025, DOI Link
View abstract ⏷
The development and screening of non-noble metal-based single-atom catalysts (SACs) are promising protocols in heterogeneous catalysis because of their low cost, maximum atom utilization, stability, reaction efficiency, and reusability. Being aware of this perspective, the present work reveals the fabrication of Co as a single-atom catalyst (Co SAC), precisely coordinated with N and O as Co–N2 O2 supported on porous carbon, via a facile pyrolytic synthetic protocol using rice husk as a carbon source and cobalt adeninate metal–organic framework, Bio-MOF-11, as the Co source. Heavily influenced by their size and environment, Co SACs exhibit remarkable catalytic performance, selectivity, and recyclability in the synthesis of quinazolinones and aromatic amines. Based on the XAS investigations, it has been established that the electronic metal–support interaction (EMSI) of Co with N and O atoms moderates the electronic nature of the isolated Co atoms, resulting in improved catalytic activity.
Correction: Ambipolar macrocycle derived from spiro-xanthene and carbazole: synthesis, structure–property relationships, electronic properties and host–guest investigation
Kodali P.K., Choppella S., Ankita, Kumar D., Pandey U.K., Ravva M.K., Singh S.P.
Erratum, Chemical Communications, 2025, DOI Link
View abstract ⏷
Correction for ‘Ambipolar macrocycle derived from spiro-xanthene and carbazole: synthesis, structure–property relationships, electronic properties and host–guest investigation’ by Phani Kumar Kodali et al., Chem. Commun., 2024, 60, 11726–11729, https://doi.org/10.1039/D4CC03440F. The authors regret that the affiliation details for Surya Prakash Singh were incorrect in the original article. The correct affiliations are as shown here. The authors also regret that an incorrect unit was used for the cavity size of the macrocycle SPS-NR-02. This was incorrectly given as 9.89 nm and 14.28 nm in the main text and in the corresponding image Fig. S15. The corrected cavit size of SPS-NR-02 is 9.89 Å between the SFX centroids and 14.28 Å between the carbazole unit centroids, and the corresponding corrected image for Fig. S15 is shown here. This correction does not affect the study’s results or conclusions. The SI file has been updated with the correct image. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.
Rational Design of TADF-Based Organic Photoredox Catalysts: Insights from DFT-Based Structure–Property Relationships
Article, Advanced Theory and Simulations, 2025, DOI Link
View abstract ⏷
Organic photoredox catalysts (OPCs) are being developed as more sustainable options for use in visible-light mediated transformations. In this study, using three donors (phenothiazine (PTZ), carbazole (CCz), and N-substituted carbazole (NCz)), four diphenyl sulfone-derived (DPS) acceptors, and two π-bridges (phenyl (Ph) and pyrimidine (Pm)), 36 donor-acceptor-donor (D–A–D) structured OPCs are designed. Density functional theory (DFT) calculations are used to predict photophysical and redox properties, including highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps, ionization potential, electron affinity, absorption energies, and excited-state redox potentials, of these OPCs. Molecules characterized by large singlet–triplet gaps (ΔES1–Tn > 0.20 eV) are fluorescent OPCs and therefore could be classified as suitable for singlet-state mediated electron transfer. CCz_DPS and CCz_Ph_DPS are potent photoreductants ((Formula presented.) < −1.70 V), and CCz_Pm_DPmS and NCz_Pm_DPyS are good photooxidants ((Formula presented.) > +1.30 V). In contrast, OPCs with smaller ΔES1–Tn (< 0.20 eV) is classified into intersystem crossing-dominant (triplet-mediated) and reverse intersystem crossing-dominant (singlet-mediated). PTZ_DPS is identified as a strong triplet-state photoreductant ((Formula presented.) (T1) = −1.73 V). Furthermore, comparison between newly designed OPCs with reported OPCs (4CzIPN and NCz-DPS) reveals that former have improved excited-state redox potentials. Overall, these findings establish essential structure–property correlations and highlight a design rationale for OPCs structured with customizable redox activities for targeted photocatalytic functions.
High Efficiency n-Type Electrochemical Doping of Homogeneous Polymeric Mixed Conductors by Aromatic Cation Insertion in Aqueous Electrolyte
Wang R., Chen J., Tan J., choppella S., Ravva M.K., Li Z., Cui Q., Xiao M., Zhang T., Yue W.
Article, Small Methods, 2025, DOI Link
View abstract ⏷
Electrochemical doping is central to energy storage, neuromorphic computing, and biosensing, yet the mechanisms governing efficient n-type doping and ion-structure correlations remain poorly understood. Here, efficient n-type electrochemical doping is reported in the polymeric mixed conductor gDPP-tB0 through tailored organic cation interactions, investigated via cyclic voltammetry, in situ spectroelectrochemistry, grazing-incidence wide-angle X-ray scattering, and molecular dynamics simulations. Compared to the choline cation (Ch+) system, the 1-ethylpyridinium cation (EPy+) system exhibited superior doping kinetics, achieving a higher reduction current density (0.47 mA cm−2), faster ion diffusion coefficient (6.77 × 10−9 cm2 s−1), more pronounced polaron generation, and improved OECT performance (µC* up to 18.7 F cm−1 V−1 s−1). These improvements stem from EPy+’s preferential backbone localization, which minimizes polymer distortion, maintains high crystallinity, and optimizes ion-electron coupling, thus resulting in more efficient n-type electrochemical doping. Moreover, further gains in doping efficiency are realized by tuning the pyridyl cation concentration and alkyl chain length. The work reveals a new paradigm for efficient n-type electrochemical doping in polymeric mixed conductors via organic cation engineering, offering new insights into the rational design of ionic liquids for enhancing n-type electrochemical doping and accelerating the development of wearable bioelectronics.
Construction of a Fluorescence-Based Logic Gate Seeing the Effect of Perchlorate Ions on Hemicyanine Dye–β-Cyclodextrin Complexes to Certify Safe Drinking Water
Anusha C.M., Dyagala S., Choppella S., Ravva M.K., Saha S.K.
Article, ChemistryOpen, 2025, DOI Link
View abstract ⏷
Perchlorate ions (ClO4−) are prevalent contaminants in the surface, and drinking water that disrupt thyroid function by competitively inhibiting the sodium-iodide symporter (NIS), posing significant health risks. Here, fluorescence-based logic gates have been constructed by leveraging the binding interactions between a hemicyanine dye, 4-[4-(dimethylamino)-styryl]-1-docosylpyridinium bromide (DASPC22) and β-cyclodextrin (β-CD) that could be useful to know whether ClO4− ions in water are within the toxicity range or not. In aqueous media, DASPC22 forms nonfluorescent H-aggregates, but fluorescence is enhanced upon forming host-guest inclusion complexes with β-CD. At low ClO4− ions concentrations, fluorescence intensity further increases due to enhanced complex stability through hydrogen bonding. ONIOM-based quantum chemical calculations have supported this phenomenon. The enhancement of fluorescence intensity of DASPC22 in the presence of β-CD and a low concentration of ClO4− ions leads to the construction of a YES logic gate that would enable one to quantify ClO4− ions’ toxicity range in water. Dual-input-single-output AND and INHIBIT logic gates with low and high concentrations of ClO4− ions, respectively, have also been constructed. The present system could be useful in addressing safety concerns related to perchlorate contamination of water.
(κ3-N∩N∩N)-Palladium Pincer Complex-Catalyzed Synthesis of Quinazolin-4(3H)-Ones Through the Acceptorless Dehydrogenation Process: Experimental Results and Computational Insights
Sivaprakash S., Goswami S., Maricherla H., Ravva M.K., Harijan D., Prabusankar G., Amali A.J., Suresh D.
Article, Organometallics, 2025, DOI Link
View abstract ⏷
In this work, the synthesis of the palladium complexes coordinated with thiazoline-derived N∩NH∩N pincer ligands and their application in the synthesis of quinazolin-4(3H)-ones through the acceptorless dehydrogenation (ADH) process along with the sequential C–C coupling reaction is presented. Initially, treatment of chloroacetyl chloride with thiazoline amine produced compound N∩NH∩CH2Cl (2), which on subsequent reaction with morpholine or piperidine afforded the corresponding N∩NH∩N pincer ligands 3 and 4. Reactions of ligands with PdCl2or Pd(OAc)2in a 1:1 molar ratio at room temperature afforded the mononuclear palladium(II) complexes [(κ3-N∩N∩N)PdX] (X = Cl, OAc) 5–8, while treatment of ligands with Pd(OAc)2in the presence of trifluoroacetic acid afforded the complexes [(κ3-N∩N∩N)Pd(TFA)] 9 and 10.1H,13C{1H} NMR spectroscopic techniques and HR-MS data confirm the proposed structures and chemical compositions. Further, molecular structures of 3, 4, 6, 8, and 10 were established through single-crystal X-ray diffraction studies. The catalytic activity of palladium(II) complexes 5–10 was evaluated for the synthesis of quinazolinone derivatives from 2-aminobenzamide and substituted benzyl alcohols via ADH coupling reactions along with sequential C–C coupling reactions. The thermodynamics associated with this transformation have been established using DFT calculations.
Fe2+- and Mn2+-Codoped CsPbCl3 Perovskite Nanocrystals for Enhancing Stability and Photophysical Performances
Banjare A., Patra D., Narayanaswamy K., Ravva M.K., Singh R.S., Singh S.P., Singh A.K.
Article, ACS Applied Nano Materials, 2025, DOI Link
View abstract ⏷
Metal doping offers a potent strategy for enhancing the optical properties and stability of CsPbCl3 (CPC) perovskites. While Mn doping has drawn attention to its unique attributes, it has failed to achieve the benchmarks set by CsPbBr3 and CsPbI3. To bridge this gap, a codoping approach involving earth-abundant and cost-effective FeCl2 has been explored in this study. PL emission peak intensity increased after codoping with various FeCl2 concentrations in Mn-doped CPC (Mn-CPC) nanocrystals. Fe2+ effectively enhances the Mn doping efficiency in CPC across 0.1-0.3 mmol concentrations by replacing some Pb2+ sites. The resultant Fe-codoped Mn-CPC nanocrystals display orange emission in hexane at 594-606 nm, boasting photoluminescence quantum yields up to 22-27%. Notably, codoped nanocrystals exhibit better photostability under ambient conditions and UV-light irradiation than Mn-CPC. The improved photoresponse characteristics induced by Fe2+ codoping highlight the potential of these nanocrystals for integration into UV-visible photodetectors and other optoelectronic devices. The electrochemical property of Fe ion-codoped Mn-CPC PNCs showed better photocurrent density results than Mn-CPC.
Novel Low-Bandgap Organic Dyads Derived from Diketopyrrolopyrrole for Efficient Single-Component Organic Solar Cells
Yadagiri B., Narayanaswamy K., Kumar V., Maricherla H., Ravva M.K., Singh S.P., Sharma G.D.
Article, Solar RRL, 2025, DOI Link
View abstract ⏷
In order to attain high performance in single-component organic solar cells (SCOSCs), it requires the designing of light-harvesting structures that can absorb light across a wide range from visible to near-infrared (NIR) wavelengths. In this investigation, two novel dyad materials, denoted as SPS-BF-Full and SPS-BT-Full are designed and synthesized, consisting of covalently linked benzofuran (BF) and benzothiophene (BT) functionalized thiophene–diketopyrrolopyrrole (TDPP) as donor and N-methyl fullero[60]pyrrolidine as the acceptor, respectively. The incorporation of a phenyl bridge between TDPP and fullero[60]pyrrolidine enhances light absorption in SPS-BF-Full and SPS-BT-Full, resulting to a high short-circuit density (JSC). Consequently, the SCOSCs utilizing SPS-BT-Full and SPS-BF-Full attained overall power conversion efficiency (PCE) of 6.28 and 7.35%, respectively. The high photovoltaic performance of OSCs utilizing SPS-BF-Full is mainly attributed to its higher external quantum efficiency and balanced hole and electron mobility (μe/μh = 1.39), along with imporved charge carrier extraction, revealing more effective charge transport in comparison to SPS-BT-Full counterparts.
Metal- and base-free spirocyclization of alkylidene oxindoles via photo- and mechanochemically-generated nitrile ylides and nitrile imines as 1,3-dipoles
Singh S., Pandey R., Christopher V., Ravva M.K., Ganguly R., Sen S.
Article, Organic Chemistry Frontiers, 2025, DOI Link
View abstract ⏷
Herein we have reported an expedient synthesis of spiro[pyrrolidine-3,3′-oxindole] and 2′-aryl-2′,4′-dihydrospiro[indoline-3,3′-pyrazol]-2-one under metal- and base-free conditions through the 3 + 2 cycloaddition reactions of in situ generated nitrile ylides and nitrile imines with alkylidene oxindoles in good to excellent yields. The nitrile ylides are generated through acetonitrile insertion onto carbenes generated from blue LED irradiation of aryl diazo esters. The nitrile imines were formed under mechanochemical conditions from diazo esters and aryl diazonium tetrafluoroborates.
Oxidative Rearrangement of 3-Aryl Azo Indoles in Water: Synthesis of C3-Oxo-C2-Amino Indoles and their Application as Fluorophores for Lipid Droplet Detection
Prabakar T., Ambastha P., Yadav R., Samanta A., Kumar Ravva M., Munshi P., Sen S.
Article, Advanced Synthesis and Catalysis, 2025, DOI Link
View abstract ⏷
A novel oxidative rearrangement of the diazene moiety in 3-aryl azo indoles is reported, leading to the formation of C3-oxo-C2-amino indoles with excellent regioselectivity. This transformation, achieved using oxone in water at ambient temperature, proceeds in good yields with broad functional group tolerance, including toward azaindoles. Mechanistic insights are gained through control experiments, crystal structures, and density functional theory calculations. Experimental and theoretical photophysical studies, along with cellular uptake and colocalization experiments, demonstrate that the resulting compounds selectively bind to lipid droplets (LDs), highlighting their potential as fluoroprobes for LD detection.
Unlocking Indazole Synthesis from α-Diazo-β-Ketoesters via Aryne Trapping: A Streamlined Approach
Guha S., Crochet A., Sukumar T., Ravva M.K., Sen S., Gremaud L.
Article, European Journal of Organic Chemistry, 2025, DOI Link
View abstract ⏷
Indazoles are high-value chemical building blocks used in medicinal chemistry and materials science for their distinct structural and functional features. This study details a [3 + 2]-cycloaddition reaction between various aryl-ketodiazoesters and ortho-(trimethylsilyl)aryl triflates under mild conditions, leading predominantly to 1-acyl-1H-indazoles. N-aryl-1H-indazoles and aryl benzoates are also observed as other products. The reaction exhibits broad functional group tolerance and scalability, making it a valuable synthetic approach. Mechanistic insights, derived from control experiments and density functional theory calculations, elucidate the cycloaddition pathway and rationalize the formation of the products. Collectively, these findings underscore the method's potential for synthesizing complex indazole derivatives, which hold significant promises for applications in pharmaceutical development and advanced materials research.
Dual-action photocatalyst: MnO2/CuO decorated 3D porous carbonaceous matrix as reusable photocatalyst for rapid removal of industrial dyes and antibiotics from contaminated-water
Pahuja M., Vishnu S., De I., Jyothirmai M.V., Sharangi S., Rani S., Jyoti, Das S., Harini E.M., Afshan M., Urkude R., Rani D., Chaudhary N., Siddiqui S.A., Ravva M.K., Singh M., Ghosh K.
Article, Journal of Environmental Chemical Engineering, 2025, DOI Link
View abstract ⏷
This study focuses on fabricating a dual-active photocatalytic cartridge material for degrading dyes and antibiotics. Hence, the in-situ uniform growth of MnO2/CuO on 3D porous high surface area carbonaceous matrix, not only efficiently degrades Eriochrome Black T (EBT - 95.40 %), Loffler's Methylene Blue (MB - 98.06 %), and azithromycin (96.50 %) within 100 min of light illumination but also reusable and stable upto 6 cycles. The mechanistic understanding based on band structure analysis, electron paramagnetic resonance technique and scavenging experiments, cumulatively explains about the participation of hydroxyl radical (•OH) at valence band of MnO2 (VBMO) and superoxide radical (•O2-) at conduction band of CuO (CBCO) in redox reactions following a Z-scheme mechanism. The theoretical studies show that the charge redistribution creates a built-in electric field between CuO-CNT-MnO2 layers, driving photogenerated electrons and holes in opposite directions, forming •O2- at CBCO and •OH at VBMO, thus enhancing degradation kinetics. The toxicity study shows 100 % cell viability with 100 minutes of dye-degraded water, 100 % bacterial viability, and healthier plants when exposed to azithromycin-degraded water, overall indicating that the degraded products are bio-compatible. A sustainable and smart prototype filter technology is demonstrated, which effectively filters 5 litres of dye/antibiotic under continuous light irradiation.
Azole-Based Diarylethenes Containing Benzoheteroarene π-Linkers for Solar Thermal Energy Storage: Influence of Aromaticity and Noncovalent Interactions
Sukumar T., Ravva M.K., Oruganti B.
Article, Journal of Organic Chemistry, 2025, DOI Link
View abstract ⏷
Diarylethene photoswitches featuring azole-based diaryl units combined with benzoheteroarene π-linkers have gained significant research interest in recent years due to their potential to achieve higher photocyclization efficiencies compared to conventional dithienylethene switches. In this work, we investigate the suitability of these photoswitches for molecular solar thermal energy storage (MOST) applications through computational modeling of their electrocyclization and cycloreversion reactions. Our calculations demonstrate that it is possible to achieve simultaneously both large energy-storage densities (0.29-0.35 MJ kg-1) and prolonged energy-storage times (half-lives of up to 124 days) under ambient conditions in dithiazolyl and dioxazolyl switches containing six distinct benzoheteroarene π-linkers. Furthermore, isomerization stabilization energy calculations and noncovalent interaction analysis reveal that the variations in energy-storage densities and times between the azole-based and dithienylethene switches stem from differences in aromaticities of the diaryl core and π-linker, as well as changes in noncovalent interactions. Notably, we demonstrate that the relative populations of photoreactive anti-parallel and non-photoreactive parallel conformers of the ring-open form of these switches are governed by weak intramolecular C···C interactions between the two aryl rings. These findings highlight the importance of optimizing such interactions to enhance energy-storage efficiencies in MOST systems.
Isolated Nickel Atomic Sites on N-Rich Nanoporous Carbon Derived from Covalent Imine Polymer as a Buchwald–Hartwig N-Arylation Catalyst
Nithya K., Anbarasan R., Anbuselvan N., Maricherla H., Ak A., Rajput P., Rana R.K., Vasantha V.S., Ravva M.K., Suresh D., Amali A.J.
Article, ACS Catalysis, 2025, DOI Link
View abstract ⏷
The ability to resemble metalloenzymes and to bridge between homogeneous and heterogeneous catalysis makes single-atom catalysts (SACs) promising for heterogeneous organic synthesis. Herein, we report the fitting of atomically isolated Ni (Ni SACs) on a nitrogen-rich (N-rich) covalent organic framework-templated carbon (Ni@N-CTC), which exhibits remarkable catalytic activity in the Buchwald–Hartwig N-arylation reaction. The demonstrated impressive catalytic activity of Ni@N-CTC is attributed to the trapping of the Ni SACs inside the N-rich nanoporous carbon matrix, which provides surplus catalytic active sites as it prevents agglomeration of Ni to form nanoparticles and ensures the preservation of the catalytically active coordinatively unsaturated nickel–nitrogen (Ni–N) sites originating from the exotic metal–support coordination and electronic interactions which were confirmed by X-ray absorption spectroscopy (XAS) analysis and computational studies.
High Performing Ambipolar Organic Electrochemical Transistors and Solid-State Inverters Enabled by Hydrophilic/Hydrophobic Side Chains Integration
Wang Y., Tan J., Hou H., Maricherla H., Ravva M.K., Zhu X., Liu R., He J., Lin Y., McCulloch I., Li Z., Yue W.
Article, Advanced Materials, 2025, DOI Link
View abstract ⏷
Progress in solid-state organic electrochemical transistors (SS-OECTs) and complementary circuits is limited by the lack of high-performance single component ambipolar mixed ionic-electronic conductors (AMIECs). Herein, two DPP-V-based terpolymers, p(gDPP-V-B05) and p(gDPP-V-B20) are designed, featuring an ambipolar backbone and tunable integrated hydrophilic/hydrophobic side-chain engineering to optimize mixed conduction. Both polymers exhibited state-of-the-art ambipolar performance in aqueous OECTs, with p(gDPP-V-B05) demonstrating the record µC* values of 384.8 F cm−1 V−1 s−1 (n-type) and 691.7 F cm−1 V−1 s−1 (p-type), along with a state-of-the-art normalized transconductance of 72.6 S cm−1for n-type. These exceptional performances are attributed to the synergistic enhancement of electronic mobility and optimized ion capacity. Aqueous inverters based on single-component p(gDPP-V-B05) delivered a high voltage gain of 393 V V−1, benefiting from well-balanced n/p-type characteristics. Notably, this material also enabled high-performing SS-OECTs, which retained strong transconductance and current output, and exhibited typical antiambipolar behavior. Furthermore, single-component solid-state inverters (SS-inverters) achieved a record-high voltage gain of 163 V V−1, representing the first SS-inverters based on AMIECs and the highest value reported for SS-inverter systems to date. These results underscore the effectiveness of the molecular design strategy and highlight the promise of ambipolar polymeric mixed ionic-electronic conductors (PMIECs) for scalable, solid-state, bio-integrated electronic circuits.
Bioengineering of Cu2O structured macro-biotemplate for the ultra-efficient and selective hand-retrieval of glyphosate from agro-farms
Parimi D.S., Jyothirmai M.V., Ravva M.K., Jaiswal A.K., Suresh A.K.
Article, Science of the Total Environment, 2024, DOI Link
View abstract ⏷
Glyphosate (Gly) is a massively utilized toxic herbicide exceeding its statutory restrictions, causing adverse environmental and health impacts. Engineered nanomaterials, even though are integral to remediate Gly, their practical use is limited due to time and energy driven purifications, and negative environmental impacts. Here, a 3D wide area (~1.6 ± 0.4 cm2) Cu2O nanoparticle supported biotemplate is designed using fish-scale wastes as a sustainable approach for the ultra-efficient and selective hand-remediation of Gly from real-time samples from agro-farms. While the innate metal binding and reducing ability of collagenous scales aided self-synthesis cum grafting of Cu2O, the selective binding potential of Cu2O to Gly facilitated its hand-retrieval; as assessed using optical characterizations, Fourier transform infrared spectroscopy, thermogravimetric analysis and liquid chromatography mass spectrometry. Optimization studies revealed extractions of diverse pay-loads of Gly between 0.1 μg/mL to 40 μg/mL per 80 mg biotemplate grafted with ~6.354 μg of sub-5 nm Cu2O and was exponential to the number of Cu2O@biotemplates. Even though pH and surfactant didn't have any impact on the adsorption of Gly to the Cu2O@biotemplates, increase in the ionic strength led to a drastic increase in the adsorption. Density function theory simulations unveiled the involvement of phosphonic and carboxylic groups of Gly for interaction with Cu2O with a bond length of 1.826 Å and 1.833 Å, respectively. Overall, our sustainably generated, cost-efficient, hand-retrievable Cu2O supported biotemplate can be generalized to extract diverse organophosphorus toxins from agro-farms and other sewage embodiments. Synopsis: Glyphosate is an excessively applied herbicide with potent health hazards and carcinogenicity. Thus, a hand removable Cu2O-supported biotemplate to selectively and efficiently remediate glyphosate from irrigation water is developed.
Exploring synthesis, characterization, and computational insights into indacenodithiophene-based hole transporting materials for enhanced perovskite solar cell applications
Article, Solar Energy, 2024, DOI Link
View abstract ⏷
Utilizing hole-transporting materials (HTMs) to extract and transport holes from perovskite materials to the electrode remains essential in most perovskite solar cell (PSC) architectures. Developing cost-effective and efficient HTMs is essential for advancing PSC technology. We have synthesized a novel HTM, TPA-IDT-TPA, which has an extended fused ring as the core moiety called indacenodithiophene (IDT) and p-methoxy triphenylamine (p-mTPA) as terminal groups. TPA-IDT-TPA exhibits appropriate frontier molecular orbital (FMO) energy levels that match perovskite materials. Density functional theory (DFT) simulations were performed to comprehend the electronic, excited-state, and charge transport properties. The DFT results indicate that the extended π-conjugation, rigidity, and the central core ring of the HTM enhanced the π-π stacking, contributing to efficient charge transport. The PSC constructed with TPA-IDT-TPA achieves a device efficiency of 8.34%, with high values of JSC and VOC, which can be further enhanced through molecular optimization.
Strategies to Enhance the Stability of Non-Fullerene Acceptor-Based Organic Solar Cells
Choppella S., Haseena S., Ravva M.K.
Article, Advanced Theory and Simulations, 2024, DOI Link
View abstract ⏷
Through comprehensive density functional theory calculations, the photodegradation mechanisms, including cis–trans isomerization, electrocyclization, and sigmatropic rearrangement reactions are investigated in indacenodithieno [3,2-b] thiophene (IT)-based non-fullerene acceptors (NFAs). Various functional group substitutions on the core (fluorine, ethyl, and cyano groups) and end groups (fluorine) of NFA are introduced to elucidate the influence of chemical modifications on photodegradation pathways. The findings reveal that the core substitution can effectively suppress electrocyclization and 1,5-sigmatropic shift reactions, which are major contributors to photodegradation. Furthermore, the electronic, excited-state, and charge transport properties of pristine and degraded products are studied to gain insights into the impact of degradation on photovoltaic parameters. The results suggest that photodegradation leads to the formation of shallow energy trap states, hindering charge transport and increasing charge recombination, ultimately affecting the power conversion efficiency of organic solar cells (OSCs). The study not only provides a comprehensive understanding of photodegradation mechanisms but also offers valuable molecular design strategies to enhance the stability of NFAs for future large-scale applications of OSCs. By establishing a clear connection between the chemical structure and photostability of NFA, this research represents a pivotal contribution to the field of organic electronics and sustainable energy technologies.
Optimization of blue LED Photo-Flow synthesis in continuous flow reactors using design of experiments (DoE): Efficient synthesis of diverse diaryl ketones
Khan H., Rajesh V.M., Ravva M.K., Sen S.
Article, Chemical Engineering Journal, 2024, DOI Link
View abstract ⏷
Herein, we demonstrated the optimization of a blue LED (450 nm) induced C-C bond formation between various aryl and heteroaryl aldehydes with 1,4-quinones at room temperature in ethyl acetate using Design of Experiments (DoE). This reaction was conducted within a flow (micro and milli-fluidic) device using a millifluidic meandering channel reactor (MC2), resulting in a library of diversely substituted diaryl ketones with moderate to good yields. Control experiments and density functional theory (DFT) based computational investigations were performed to elucidate the reaction mechanism.
Photolytic ortho-Selective Amino Pyridylation of Aryl Isocyanates with N-Amino Pyridinium Ylides for the Synthesis of N-Arylsulfonyl Ureas
Rath S., Patel S., Choppella S., Menon P., Garain T., Banerjee S., Ravva M.K., Sen S.
Article, Journal of Organic Chemistry, 2024, DOI Link
View abstract ⏷
Herein, we report an expedient synthesis of aryl sulfonyl ureas 4 and 5 from N-amino pyridinium ylides and aryl isocyanates. N-Aminopyridinium ylides 3 are synthesized via blue light-emitting diode irradiation of pyridine/isoquinoline and appropriate iminoiodinanes. The strategy involved a hitherto unknown carboamination of imine moieties (of aryl isocyanates) via a three-component reaction of pyridine derivatives/isoquinoline 1, N-aryl sulfonyl iminoiodinanes 2, and numerous aryl isocyanates at room temperature in 2-methyl tetrahydrofuran to afford the target compounds in moderate to excellent yields. N-Arylpyridinium ylides 3 (as intermediates) undergo a [3+2] cycloaddition with the aryl isocyanates followed by the aromatization of the pyridine/isoquinoline moiety to afford compounds 4. On the basis of the substitution pattern among the reactants, in some cases pyridine extrusion occurs during the reaction to afford depyridinylated aryl sulfonyl ureas 5. In general, isocyanates are used as dipolarophiles in [3+2] cycloaddition reactions. However, regioselective amino pyridylation of these species is a first. Control experiments and density functional theory calculations elucidate the reaction mechanism. The batch process of the protocol could be seamlessly transferred to the photoflow synthesis.
Ambipolar macrocycle derived from spiro-xanthene and carbazole: synthesis, structure-property relationships, electronic properties and host-guest investigation
Kodali P.K., Choppella S., Ankita N., Kumar D., Pandey U.K., Ravva M.K., Singh S.P.
Article, Chemical Communications, 2024, DOI Link
View abstract ⏷
For the first time, we present the detailed synthesis, photophysical, electrochemical, host-guest and charge transport properties of spiro[fluorene-9,9′-xanthene] (SFX) and carbazole macrocycle SPS-NR-02. The electron and hole transport values measured using the space charge limited current (SCLC) method resulted in ambipolar charge transport with an electron to hole mobility ratio of 0.39.
Impact of Surrounding Environment on Hot-Exciton Based Organic Emitters for TADF Applications
Article, ChemPhotoChem, 2024, DOI Link
View abstract ⏷
Understanding thermally activated delayed fluorescence (TADF) in solid-state environments is crucial for practical applications. However, limited research focuses on how the medium affects TADF properties of hot-exciton-based emitters. In our study, we calculated and compared reverse intersystem crossing, radiative, and non-radiative decay rates of TADF emitters in gas, solvent, and solid phases. The designed emitters have a donor-acceptor-donor (D-A-D) structure, with donors such as triphenylamine (TPA) and diphenylamine thiophene (ThPA), combined with acceptors such as benzothiadiazole (BT), pyridine thiadiazole (PT) and thiadiazolobenzopyridine (NPT). We model the solvent and solid phases with the polarizable continuum model (PCM) and quantum mechanical/molecular mechanics (QM/MM) methods, respectively. Using density functional theory (DFT) and time-dependent DFT, we analyze how TADF emitters′ geometrical, electronic, and excited-state properties vary in these phases. Our results show that the solid-state environment significantly influences the geometry and TADF properties of emitters. In the presence of solid medium, our study indicates that non-radiative decay rates tend to be slower. On the other hand, radiative emission rates were found to be less influenced by the properties of the surrounding medium. Overall, our study connects emitter chemical structure and the surrounding environment‘s impact on excited-state characteristics and photochemical properties.
R-BINOL-Chiral Phosphoric Acid Catalyzed Regioselective Synthesis of 7-Oxo-Pyrazolo[1,2-a]Pyrazoles via [3+2] Cycloaddition Reaction of Morita Baylis Hillman Adducts with N, N’-Cyclic Azomethine Imines
Karthikeyan S., Choppella S., Murali A.C., Subimol K.R., Monica J.H.R., Ravva M.K., Kumar Ayyanoth K.K.
Article, ChemistrySelect, 2024, DOI Link
View abstract ⏷
We report an efficient [3+2] cycloaddition protocol for the synthesis of pyrazolo[1,2-a]pyrazolones from Morita-Baylis-Hillman adducts and N,N’-cyclic azomethine imines. The R-BINOL chiral phosphoric acid was identified as the suitable catalyst for the reported cycloaddition protocol. Almost all MBH adducts regioselectively delivered 7-oxo-pyrazolo[1,2-a]pyrazoles at an efficient yield of 69–91 %. With exception, the MBH adducts derived from acrylonitrile deliver 5-oxo-pyrazolo[1,2-a]pyrazoles comparatively at a higher yield than the 7-oxo-pyrazolo[1,2-a]pyrazoles. The density functional theory (DFT) studies demonstrate that the reaction is thermodynamically more feasible in the presence of R-BINOL chiral phosphoric acid.
Design of Isoindigo-Based Small-Molecule Donors for Bulk Heterojunction Organic Solar Cell Applications in Combination with Nonfullerene Acceptors
Karuppusamy M., Panneer S.V.K., Varathan E., Ravva M.K., Easwaramoorthi S., Subramanian V.
Article, Journal of Physical Chemistry A, 2024, DOI Link
View abstract ⏷
The development of small-molecule organic solar cells with the required efficiency depends on the information obtained from molecular-level studies. In this context, 39 small-molecule donors featuring isoindigo as an acceptor moiety have been meticulously crafted for potential applications in bulk heterojunction organic solar cells. These molecules follow the D2-A-D1-A-D2 and D2-A-π-D1-π-A-D2 framework. Similar molecules considered in the previous experimental study (molecules R1 ((3E,3″E)-6,6″-(benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(1,1′-dimethyl-[3,3′-biindolinylidene]-2,2′-dione)) and R2 ((3E,3″E)-6,6″-(4,8-dimethoxybenzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(1,1′-dimethyl-[3,3′-biindolinylidene]-2,2′-dione))) have been chosen as reference molecules. Molecules with and without π-spacers have been considered to understand the impact of the length of the π-spacer on intramolecular charge-transfer transitions and absorption properties. A detailed investigation is carried out to establish the relationship between the structure and photovoltaic parameters using density functional theory and time-dependent density functional theory methods. The newly developed molecules exhibit better electronic, excited-state, and charge transport properties than the reference molecules. Additionally, model donor-acceptor interfaces are constructed by integrating the designed donor molecules with fullerene/nonfullerene acceptors. The electronic and excited-state properties of these interfaces are rigorously evaluated. Results elucidate that the donor comprising of isoindigo-bithiophene-pyrroloindacenodithiophene (IIG-T2-PIDT) emerges as a promising candidate for bulk heterojunction solar cells based on nonfullerene acceptors. This research provides systematic design strategies for the development of small-molecule donors for organic solar cells.
Computational design of efficient corannulene-based Non-Fullerene acceptors for organic solar cells applications
Article, Journal of Photochemistry and Photobiology A: Chemistry, 2024, DOI Link
View abstract ⏷
In our study, we aimed to enhance the optoelectronic properties of corannulene through functionalization for use as a non-fullerene acceptor (NFA) in organic solar cells. To achieve this, we designed new corannulene derivatives by introducing various electron-donating and electron-withdrawing groups onto the corannulene core. Geometric, electronic, optical, and charge transport properties of newly designed molecules are analyzed using long-range corrected density functional theory methods. The potential NFA is identified by conducting extensive analysis, such as light absorption properties, ground-state dipole moments, and the energy difference between LUMO and LUMO+1 orbitals. Also, a model donor–acceptor interface is constructed by considering PTQ10 oligomer as the donor and corannulene derivatives as acceptors. Charge-transfer states and exciton dissociation processes are analyzed at the polymer chain and NFA interface. Overall, the results obtained from this study can provide useful guidance in designing high-performing NFAs.
Molecular Electron Density and Electrostatic Potential and Their Applications
Panneer S.V.K., Karuppusamy M., Balamurugan K., Mudedla S.K., Ravva M.K., Subramanian V.
Book chapter, Electron Density: Concepts, Computation and DFT Applications, 2024, DOI Link
View abstract ⏷
The critical features of atomic or molecular scalar fields can be captured by mapping their topography. The topography maps, viz., molecular electron density (MED) and molecular electrostatic potential (MESP), are successfully used to characterize the weak interactions that exist in systems ranging from small molecular clusters to large supramolecular systems. Topography mapping mainly involves identifying and characterizing their critical points (CPs). These CPs are extremely useful for describing the nature of weak interactions and quantifying the strength of interaction. The first part of the chapter delineates fundamental concepts related to MED and MESP. Later, the usefulness of MED and MESP analyses for understanding weak interactions is demonstrated by taking various molecular complexes.
Efficient photocatalytic green hydrogen production using crystalline elemental Boron nanostructures under visible light
Article, International Journal of Hydrogen Energy, 2024, DOI Link
View abstract ⏷
Green Hydrogen emerges as a promising energy solution in the quest for achieving Net Zero goals. The application of particulate semiconductors in photocatalytic water splitting introduces a potentially scalable and economically viable technology for converting solar energy into hydrogen. Overcoming the challenge of efficiently transferring photoelectrons and photoholes for both reduction and oxidation on the same catalyst is a significant hurdle in photocatalysis. In this context, we introduce highly efficient crystalline elemental boron nanostructures as photocatalysts, employing a straightforward and scalable synthesis method yield green hydrogen production without the need for additional co-catalysts or sacrificial agents. The resulting photocatalyst demonstrates stability and high activity in H2 production, achieving over 1 % solar-to-hydrogen energy conversion efficiency (>15,000 μmol. g−1.h−1) during continuous 12-h illumination. This efficiency is credited to broad optical absorption and the crystalline nature of boron nanostructures, paving the way for potential scale-up of reactors using crystalline boron photocatalysts.
Functionalized Graphene-Incorporated Cupric Oxide Charge-Transport Layer for Enhanced Photoelectrochemical Performance and Hydrogen Evolution
Krishna A.M.S., Ramasubramanian B., Haseena S., Bamola P., Sharma H., Mahata C., Chroneos A., Krishnamurthy S., Ravva M.K., Chandu B., Lim Y.-F., Kumar A., Ramakrishna S., Biring S., Chakrabortty S., Dalapati G.K.
Article, Catalysts, 2023, DOI Link
View abstract ⏷
The production of hydrogen (H2) through photoelectrochemical water splitting (PEC-WS) using renewable energy sources, particularly solar light, has been considered a promising solution for global energy and environmental challenges. In the field of hydrogen-scarce regions, metal oxide semiconductors have been extensively researched as photocathodes. For UV-visible light-driven PEC-WS, cupric oxide (CuO) has emerged as a suitable photocathode. However, the stability of the photocathode (CuO) against photo-corrosion is crucial in developing CuO-based PEC cells. This study reports a stable and effective CuO and graphene-incorporated (Gra-COOH) CuO nanocomposite photocathode through a sol-gel solution-based technique via spin coating. Incorporating graphene into the CuO nanocomposite photocathode resulted in higher stability and an increase in photocurrent compared to bare CuO photocathode electrodes. Compared to cuprous oxide (Cu2O), the CuO photocathode was more identical and thermally stable during PEC-WS due to its high oxidation number. Additionally, the CuO:Gra-COOH nanocomposite photocathode exhibited a H2 evolution of approximately 9.3 µmol, indicating its potential as a stable and effective photocathode for PEC-WS. The enhanced electrical properties of the CuO:Gra-COOH nanocomposite exemplify its potential for use as a charge-transport layer.
Oxidative Aminopyridylation of Maleimides and 1, 4-Quinones with N-Aminopyridinium Ylides at Room Temperature in the Absence of External Reagents
Barman D., Rath S., Kumar Ravva M., Jacob J.M., Sen S.
Article, Advanced Synthesis and Catalysis, 2023, DOI Link
View abstract ⏷
Herein we have reported an expedient di-functionalization of such versatile scaffolds. By harnessing an under explored reactivity of N-aminopyridinium ylides, we have developed an aminopyridylation of N-substituted maleimides and 1, 4-quinones at room temperature in 2-methyl THF without any external reagents. The [3+2] cycloaddition of N-aminopyridinium ylides generate the corresponding cycloadduct with various maleimides and 1, 4-quinone substrates, which rapidly undergoes oxidation at the alkene moiety under open air, inducing a considerable driving force, thermodynamically, to facilitate aromatisation of the pyridine and a subsequent homolytic cleavage of the N−N bond to generate the desired 2, 3-aminopyridylated products in good to excellent yield. Experimental and computational studies clarify the reaction mechanism.
Mechanochemical Metal-free N-Sulfonyl Transfer Reaction: Expedient Synthesis of N-Sulfonyl Amidines
Guha S., Maheshwari S., Ravva M.K., Jacob J.M., Yadav S., Sen S.
Article, Asian Journal of Organic Chemistry, 2023, DOI Link
View abstract ⏷
An operationally simple mechanochemical reaction between iminoiodinanes with numerous cyclic 2°-amines such as morpholine, piperidine, pyrrolidine, thiomorpholine, N-Boc diazepine and N-Boc piperazine has been reported to afford N-sulfonyl amidines in moderate to excellent yield. The N-sulfonyl transfer reaction happens in a ball mill apparatus (RETSCH 400™) with three 5 mm stainless steel (ss) balls in a 5 mL stainless steel (ss) reaction jar with 2-methyl tetrahydrofuran as liquid assisted grinding auxiliary (LAG). This metal catalyst-base free synthesis with minimal solvents (as LAGs) demonstrated an efficient N-sulfonyl transfer reaction from iminoiodinanes. N-sulfonyl amidines are ubiquitous building blocks present in natural products and drug intermediates. Control experiments and computational studies based on density functional theory (DFT) calculations were performed to gain deeper insight into the mechanism.
Metal-free synthesis of N-sulfonyl imines from benzyl alcohol derivatives and iminoiodinanes via mechanochemistry
Guha S., Bhattacharya R., Jacob J., Ravva M., Sen S.
Article, Organic and Biomolecular Chemistry, 2023, DOI Link
View abstract ⏷
An expedient and operationally convenient mechanochemical synthesis of aryl/heteroaryl N-sulfonyl imines is reported by reacting iminoiodinanes with numerous aryl/heteroaryl benzyl alcohols in ball milling apparatus (RETSCH 400™) with three 5 mm stainless steel (ss) balls in a 5 mL stainless steel (ss) reaction jar. CHCl3 (η = 0.2-0.4 μL mg−1) was used as a liquid assisted grinding (LAG) auxiliary. This metal catalyst- and base- free synthesis with nominal amounts of solvents (as LAGs) demonstrated an efficient N-sulfonyl transfer reaction from iminoiodinanes to afford the desired compounds in moderate to good yields. Substituted N-sulfonyl imines are crucial as standalone natural product building blocks and drug intermediates as well as precursors of sulfonamides which have been involved in potential small molecule therapy in many therapeutic programs. The putative mechanisms of the transformations are discussed based on control reactions and DFT calculations.
Application of Newly Designed Y-Series Nonfullerene Acceptors for High-Efficient Organic Solar Cells
Article, Advanced Theory and Simulations, 2023, DOI Link
View abstract ⏷
The electron acceptor materials in organic solar cells (OSCs) play an essential role in enhancing power conversion efficiency (PCE). Although Y6-based nonfullerene acceptors (NFAs) have shown fascinating experimental progress, molecular engineering is an effective strategy for further improvement of PCE. Herein, a series of Y6-based symmetric and asymmetric NFAs are designed using the Y6-based core with various end-group units. The impact of end group units on geometric, electronic, and excited state properties of NFAs is studied using state-of-the-art density functional theory methods. Various selection criteria are used to screen potential NFAs among 18 newly designed NFAs. The interfacial electronic properties between conjugated polymer and NFAs are thoroughly studied in the excited state to analyze the potentiality of screened NFAs. More importantly, the screened asymmetric NFAs have shown improved charge mobilities with a lower charge recombination rate than prototype FRY6. It is noticed that screened NFAs have multiple charge transfer pathways through direct excitation, hot excitons, and intermolecular electric field mechanisms. Overall, the results obtained from this computational study give useful guidance for developing NFAs for high-performance OSCs.
Computational design of efficient near-infrared TADF emitters with hot-exciton characteristics
Jacob J.M., Samanta P.K., Ravva M.K.
Article, New Journal of Chemistry, 2023, DOI Link
View abstract ⏷
Developing near-infrared (NIR) TADF emitters is challenging due to the inherent energy gap law. In this work, we designed a set of twelve donor-acceptor1-acceptor2 (D-A1-A2) type NIR pure organic emitter molecules that contain a strong donor (triphenylamine (TPA)), a cyano group substituted anthrathiadiazole (AZ) unit as A1, and fused aromatic/heterocyclic molecules as the A2 unit. The strength of the acceptor part A2 is altered by introducing electron-withdrawing groups (-H, -F, -CN). We studied their geometrical, electronic, and excited state properties using Density functional theory (DFT) and time-dependent DFT methods. Comprehensive analysis of excited state properties obtained from computational methods such as the energy gap between singlet and triplet excited states (ΔEST), spin-orbit coupling (SOC) values, the nature of singlet and triplet excited states, rates of reverse intersystem crossing (kRISC), and radiative and non-radiative emissions (kr and knr) are conducted to acquire insights into the NIR emission in the studied molecules. Our calculated results show that the molecules should possess hybrid localized and charge transfer (HLCT) character dominated by Frenkel-type excitation (LE) in the lowest singlet excited state to achieve faster kr. Furthermore, the strong donor, AZ unit, and moderate acceptor A2 unit provide smaller energy gaps between singlet and triplet states with reasonable SOC values in the higher excited states. In our study, we identify multiple hot-exciton channels to up-convert dark triplet excitons into bright singlet excitons, which might improve the exciton utilization efficiency.
Structure-aromaticity-spectroscopy relationship in conjugated polymers
Karuppusamy M., Panneer S.V.K., Jennifer G A., Varathan E., Ravva M.K., Subramanian V.
Article, Theoretical Chemistry Accounts, 2023, DOI Link
View abstract ⏷
In this study, an effort has been made to analyze the aromaticity of oligomers of phenylenes and thiophenes, with the presence and absence of linkers using Nucleus-Independent Chemical Shift (NICS) as a descriptor. The relation between HOMO–LUMO gaps, reorganization and excitation energies with respective NICS values has been employed to develop a structure-aromaticity-conjugation spectroscopy relationship (SACSR). Results show that HOMO–LUMO gaps/excitation energies of various model systems exhibit linear relationships with the inverse of the NICS values, indicating the possible existence of the SACSR.
Designing Donor-Acceptor-Donor (D-A-D) Type Molecules for Efficient Hole-Transporting in Perovskite Solar Cells – A DFT Study
Paramasivam G., Sambasivam S., Kumar Ravva M.
Article, ChemistrySelect, 2023, DOI Link
View abstract ⏷
We designed eight hole-transporting materials (HTMs) of D-A-D type comprising an acceptor (A) unit flanked between two triphenylamine (TPA) donor (D) units. The structural, electronic, and absorption properties of designed molecules are studied using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The MPW1PW91 functional with a 6-31g(d,p) basis set was chosen, followed by a careful benchmark of DFT functionals. We identified dibenzothiophene-triphenylamine (DBT-TPA) and dibenzo-1,4-dioxaspiro[4,4]nonane-triphenylamine (DBDN-TPA) as the most promising molecules due to their unique properties, such as finite π-conjugation, suitable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), deep blue absorption, and lower reorganization energy than the recently reported anthradithiophene–triphenylamine (ADT-TPA) based HTMs. Furthermore, the newly proposed D-(L-A-L)-D type molecules with a linker (L) display the enhanced features required for improved hole mobility. Our work demonstrates the fine-tuning of electronic interactions between the donor and acceptor units, with a linker (L), in achieving the planarity, absorption, and hole mobility essential for efficient HTMs in perovskite solar cells.
Modulating the strength of acceptor in D-A-D type hole transport materials for efficient inverted perovskite solar cells
Paramasivam G., Sambasivam S., Ravva M.K.
Article, Chemical Physics, 2023, DOI Link
View abstract ⏷
We report herein a design strategy to improve the hole mobility of D-A-D-based hole transport material (HTM) by modifying the accepting core of the reference HTMs based on triphenylamine (TPA) and bithieno thiophene (BTTI) units. Eight HTMs are designed by replacing the BTTI unit in BTTI-TPA HTM with several commonly available diones and imides as acceptors. The structural, electronic, optical, and charge transport properties are studied using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The designed molecules are extensively examined for their structural, electronic, and absorption properties to extract the features that improve their hole mobility using the MPW1PW91/6–31 g(d,p) method. We identified four carefully designed BTTD-TPA, DBTT-TPA, NDTTI-TPA, and NDTI-TPA molecules as the most promising HTMs. This work exemplifies the role of the methyl group on electron acceptors on hole reorganization energies. Results obtained from this study provide valuable guidelines for designing efficient HTMs.
Improving the TADF in Corannulene-Based Emitters via Tuning the Strength of Donor and Acceptor Groups
Jacob J.M., Jennifer G A., Varathan E., Ravva M.K.
Article, Advanced Theory and Simulations, 2023, DOI Link
View abstract ⏷
In this investigation, a systematic study on the design and development of corannulene-based thermally activated delayed fluorescence (TADF) emitters using density functional theory methods is carried out. Benzene, benzopyrazine, difluoro-benzopyrazine, benzene-1,2-dithiol, and tetrasulfone are introduced on corannulene bowl as electron-withdrawing groups to alter the electron-accepting property of corannulene. Three different donors, viz., carbazole, phenoxazine, and 5,10-dihydrophenazine are substituted on the rim position of corannulene to alter the absorption properties. The relationship between chemical structure and TADF property is established by evaluating the dihedral angle between donor and acceptor units, spin–orbit coupling (SOC) values, the energy difference between singlet-triplet excited states (ΔEST), and rates of reverse intersystem crossing (kRISC). The newly designed TADF emitters show absorption in the blue to near-IR regions depending on the strength of the donor and acceptor moieties. Careful analysis of these properties delineates the relationship between SOC values and the nature of the excited states, which is crucial for achieving high kRISC.
Understanding the Stability of π-Conjugated Diradicaloid Organic Molecules
Choppella S., Paramasivam G., Sambasivam S., Ravva M.K.
Article, Journal of Electronic Materials, 2023, DOI Link
View abstract ⏷
π-Conjugated open-shell diradicaloid molecules have various applications in organic electronics. Herein, we have computationally designed 20 diradicaloids. The designed diradicaloids consist of a π-bridge flanked between two carbene-derived end groups. We describe how the diradicaloid property of these molecules can be tuned through the choice of carbene end groups and π-bridge. We quantified the diradical character of newly designed molecules using diradical indices (Y0) and (Y1), the fractional occupation number weighted electron density (NFOD), and singlet–triplet energy gaps (ΔEST). The performance of a wide range of density functional theory (DFT)-based methods is validated using complete active space self-consistent field (CASSCF) results. Global hybrid functional BHandHLYP provides the best accuracy among all DFT methods. Our results indicate that several diradicaloids are promising materials for organic electronics.
Synthesis and structural investigation of mononuclear penta- and hexa-coordinated Co complexes of 8-hydroxyquinoline derived ligands
Kumari T., Meena R., Giri L., Sarma B., Angarkhe P.R., Jacob J.M., Tripathy J., Joshi J., Ravva M.K., Behera R.K., Mohapatra S.K.
Article, Journal of Molecular Structure, 2023, DOI Link
View abstract ⏷
This article describes the synthesis and structural property investigation of two new mononuclear Co(II) complexes of 8-hydroxyquinoline derived flexible tridentate N,O,N'- (LI) and tetradentate N,O,O',N'-ligands (LII). The reactions were carried out between CoCl2.6H2O and the respective ligands in methanol to obtain the complexes CoLICl2 and CoLIICl2 in good yields. The complexes are characterized by elemental analysis, mass, IR spectroscopy, and single-crystal X-ray diffraction. The molecular structure of CoLICl2 shows distorted trigonal bipyramidal coordination geometry with the structural index parameter τ = 0.83. The apical positions are occupied with the quinoline O- and one terminal Cl-atom, whereas the equatorial positions are held by the two N-atoms and the second Cl-atom. In contrast, CoLIICl2 has a slightly distorted octahedral structure with all the donor atoms of the chelating ligand LII holding the equatorial positions with the two-terminal Cl-atoms at the apical positions. Electronic structure calculations are used to evaluate the geometrical, electronic, and magnetic properties of these complexes. Non-periodic calculations used to simulate molecules indicate a strong dπ-pπ bonding between Co and ligands. The crystal packing from both the solid-state structures revealed further stability of the molecule via weak non-covalent interactions through π.…π stacking between quinoline rings and C–H.…Cl hydrogen bonding. A detailed comparison between the geometric parameters of CoL1Cl2 and CoLIICl2 are reported. In addition, the comparison of selected structural parameters between a range of transition metal quinolates from the literature are given. Periodic calculations to simulate crystals using B3LYP hybrid functional predicts both the crystalline structures to be magnetic insulators.
Theoretical Insights into the Optical and Excited State Properties of Donor-Phenyl Bridge-Acceptor Containing Through-Space Charge Transfer Molecules
Sivasakthi P., Jacob J.M., Ravva M.K., Samanta P.K.
Article, Journal of Physical Chemistry A, 2023, DOI Link
View abstract ⏷
A comparative new strategy to enhance thermally activated delayed fluorescence (TADF) of through-space charge transfer (CT) molecules in organic light-emitting diodes (OLEDs) is investigated. Generally, TADF molecules adopt a twisted donor and acceptor structure to get a sufficiently small ΔEST and a higher value of the spin-orbit coupling matrix element (SOCME). However, molecules containing donor-phenyl bridge-acceptor (D-p-A) units and featuring π-stacked architectures have intramolecular CT contribution through space and exhibit high TADF efficiency. We have explored the insights into the TADF mechanism in D-p-A molecules using the density functional theory (DFT) and time-dependent DFT methods. The calculated optical absorption and ΔEST values are found to be in good agreement with available experimental data. Interestingly, we found the origin of the SOCME to be the twisted orientation of the donor and bridge moieties. Also, we predicted similar molecules with enhanced OLED efficiency with different substitutions.
n-Type Organic Electrochemical Transistors with High Transconductance and Stability
Wang Y., Zhu G., Zeglio E., Castillo T.C.H., Haseena S., Ravva M.K., Cong S., Chen J., Lan L., Li Z., Herland A., McCulloch I., Inal S., Yue W.
Article, Chemistry of Materials, 2023, DOI Link
View abstract ⏷
An n-type conjugated polymer based on diazaisoindigo (AIID) and fluorinated thiophene units is introduced. Combining the strong electron-accepting properties of AIID with backbone fluorination produced gAIID-2FT, leading to organic electrochemical transistors (OECTs) with normalized values of 4.09 F cm-1 V-1 s-1 and a normalized transconductance (gm,norm) of 0.94 S cm-1. The resulting OECTs exhibit exceptional operational stability and long shelf-life in ambient conditions, preserving 100% of the original maximum drain current after over 3 h of continuous operation and 28 days of storage in the air. Our work highlights the advantages of integrating strong electron acceptors with donor fluorination to boost the performance and stability of n-type OECTs.
Cyclo[18]carbon‐A new class of electron acceptor for organic solar cells applications
Haseena S., Maiyelvaganan K.R., Prakash M., Ravva M.K.
Article, Journal of Molecular Structure, 2023, DOI Link
View abstract ⏷
The all-carboatomic ring, cyclo[18]carbon (C18), has the potential to act as an electron acceptor due to promising electronic and optical properties. In this study, we first illustrated the geometrical, electronic, and excited-state properties of C18 using various hybrid and long-range corrected density functional theory (DFT) methods. Further, we studied the nature of intermolecular interactions between dimers of C18 to gain insights into packing configurations of cyclo[18] in dimer and trimer configurations. Also, using the state-of-the-art DFT methods, we have reported the thorough characterization of the lowest excited-state (i.e. charge-transfer state) in various donor-acceptor model complexes based on pentacene and C18. We established an interplay between the molecular packing of C18 and pentacene molecules on the energy of charge transfer state. All these results could help in the designing of more efficient organic solar cells.
A DFT Study on the Relationship Between Molecular Structure and Electron Transport in Molecular Junctions
Article, Journal of Electronic Materials, 2023, DOI Link
View abstract ⏷
Here we report how the chemical functionalization of the bridge molecule influences the electronic properties of conjugated terthiophene and the electronic coupling, i.e., the linkage between molecule and electrode, using density functional theory (DFT) methods. Furthermore, we explore the modulation in electron transport properties of molecular junctions with various functional derivatives utilizing a combination of DFT and electron transport non-equilibrium Green’s function (NEGF) calculations.
Electronic structure and origin of intrinsic defects in sputtered HfTiO2 alloy dielectric on GaAs surface
Mahata C., Jyothirmai M.V., Ravva M.K., Chakrabortty S., Kim S., Biring S., Ramakrishna S., Dalapati G.K.
Article, Journal of Alloys and Compounds, 2022, DOI Link
View abstract ⏷
In this work, we have investigated the electronic structure and electrical properties of sputter-deposited high-k dielectrics grown on p-GaAs substrate with post-deposition annealing at 500 °C/N2 ambient. Capacitance-voltage results show that co-sputtered amorphous-HfTiO2 alloy dielectric can reduce interfacial dangling bonds. HRTEM and AR- X-ray photoelectron spectroscopy results confirmed the formation of a thin interfacial layer during sputter deposition. At the atomistic level, the surface reaction and electronic interface structure were investigated by density-functional theory (DFT) calculations. Using the HSE functional, theoretical calculations of bulk HfO2, a-TiO2, and HfTiO2 band gaps are found to be 5.27, 2.61, and 4.03 eV, respectively. Consequently, in the HfTiO2/GaAs interface, the valance band offset is found to be reduced to 1.04 eV compared to HfO2/GaAs structure valance band offset of 1.45 eV. Reduction in border trap density (~1011 V/cm2) was observed due to Ti atoms bridging between As-dangling bonds. The angle-resolved XPS analysis further confirmed Ti-O-As chemical bonding with very thin (~20 Å) dielectric layers.
Side chain engineering enhances the high-temperature resilience and ambient stability of organic synaptic transistors for neuromorphic applications
Zhao Y., Haseena S., Ravva M.K., Zhang S., Li X., Jiang J., Fu Y., Inal S., Wang Q., Wang Y., Yue W., McCullocn I., He D.
Article, Nano Energy, 2022, DOI Link
View abstract ⏷
Organic synaptic transistors are considered to be one of the most promising device concepts for neuromorphic systems. However, repressively low memory retention and high-temperature instability greatly preclude the development and real-world application of organic synaptic transistors. Herein, we reported three conjugated polymers based on a bithiophene-thienothiophene backbone and the traditional ethylene glycol (EG) chains substituted by more hydrophobic propylene glycol (PG) and butylene glycol (BG) counterparts for three-terminal organic neuromorphic memory devices (TONMD). The resulting TONMD exhibits superior viability in ambient and high-temperature environments. BG chain-based p(b2T-TT) show ultra-long memory retention of over 103 s and large analog switching range (>10 ×) at 180 °C, which represents the record-high high-temperature resilience for reported TONMD to date. They also demonstrated excellent endurance of over 105 write-read operations and ultra-high ambient stability with 96 % of its original conductance after 3 months. Data of molecular dynamic simulations and microstructure show that the superior high-temperature resilience and ambient stability originate from more rigid conformation and stable morphology with the increased hydrophobicity of the PG and BG functionalities. Overall, rational design of oligoether side-chains will boost the device's dual high-temperature and ambient stability without compromising synaptic function and provide promising strategies for high-temperature neuromorphic applications.
Theoretical studies on donor–acceptor based macrocycles for organic solar cell applications
Article, Scientific Reports, 2022, DOI Link
View abstract ⏷
We have designed a series of new conjugated donor–acceptor-based macrocyclic molecules using state-of-the-art computational methods. An alternating array of donors and acceptor moieties in these macrocycle molecules are considered to tune the electronic and optical properties. The geometrical, electronic, and optical properties of newly designed macrocyclic molecules are fully explored using various DFT methods. Five conjugated macrocycles of different sizes are designed considering various donor and acceptor units. The selected donor and acceptors, viz., thiophene (PT), benzodithiophene (BDT), dithienobenzodithiophene (DTBDT), diketopyrrolopyrrole (DPP), and benzothiazole (BT), are frequently found in high performing conjugated polymer for different organic electronic applications. To fully assess the potential of these designed macrocyclic derivatives, analyses of frontier molecular orbital energies, excited state energies, energy difference between singlet–triplet states, exciton binding energies, rate constants related to charge transfer at the donor–acceptor interfaces, and electron mobilities have been carried out. We found significant structural and electronic properties changes between cyclic compounds and their linear counterparts. Overall, the cyclic conjugated D–A macrocycles’ promising electronic and optical properties suggest that these molecules can be used to replace linear polymer molecules with cyclic conjugated oligomers.
Changes in structure and stability of lithium polysulfides encapsulated in carbon nanotubes: A DFT study
Article, Journal of Molecular Liquids, 2022, DOI Link
View abstract ⏷
Lithium-sulfur (Li[sbnd]S) batteries are emanating as the next generation alternatives for rechargeable batteries. However, the loss of capacity and self-discharge due to the dissolution of lithium polysulfides hinders their practical applications. In this study, we performed density functional theory simulations to explore the importance of carbon nanotubes (CNTs) as possible anchoring channels to immobilize soluble lithium polysulfides (Li2S2n, where n = 2,3, and 4). We quantitatively investigated the interplay between confinement effects and interaction energy of Li2S2n species with CNT to address the shuttling effect. Our results demonstrate that the interaction between CNTs and lithium polysulfides is governed by electrostatic interactions. Based on the interaction energies, Charge transfer analysis, and density of states, we found that CNTs facilitate the immobilization of Li2S2n. Results obtained from this study will provide useful guidelines to improve the performance of Li[sbnd]S batteries.
Rational design of fused-ring based non-fullerene acceptors for high performance organic solar cells
Haseena S., Jyothirmai M.V., Kumar Ravva M.
Article, Solar Energy, 2022, DOI Link
View abstract ⏷
In this study, we have designed 56 new non-fullerene acceptors (NFAs) by rational design of end-cap manipulation and core modification using density functional theory methods. Geometrical, electronic, and excited state properties of these newly designed molecular are thoroughly characterized using the state-of-the-art density functional theory methods. The influence of end-cap groups on various core units is studied by comparing the absorption wavelengths, lowest excitation energies, ground-state dipole moments and, excited state dipole moments. Results obtained from these analyses reveal the importance of choosing the right combination of end-cap and core units. The potential NFAs are screened using selection criteria such as energy gap between the LUMO of polymer donor and the LUMO of NFA, based on the energy difference between LUMO and LUMO + 1 of NFAs, energy gap between the HOMO of polymer donor and LUMO of NFA, dipole moments, and quadrupole moments of NFA. Furthermore, donor–acceptor interfaces are constructed using potentials NFAs and the PM6 polymer donor. Charge-transfer state, exciton dissociation, and charge separation processes are analyzed at the polymer/NFA interfaces. Overall, results obtained from these analyses provide valuable guidelines for designing potential NFA that could enhance photovoltaic devices' efficiency.
Engineering colloidally stable, highly fluorescent and nontoxic Cu nanoclusters via reaction parameter optimization
Busi K.B., Kotha J., Bandaru S., Ghantasala J.P., Haseena S., Bhamidipati K., Puvvada N., Ravva M.K., Thondamal M., Chakrabortty S.
Article, RSC Advances, 2022, DOI Link
View abstract ⏷
Metal nanoclusters (NCs) composed of the least number of atoms (a few to tens) have become very attractive for their emerging properties owing to their ultrasmall size. Preparing copper nanoclusters (Cu NCs) in an aqueous medium with high emission properties, strong colloidal stability, and low toxicity has been a long-standing challenge. Although Cu NCs are earth-abundant and inexpensive, they have been comparatively less explored due to their various limitations, such as ease of surface oxidation, poor colloidal stability, and high toxicity. To overcome these constraints, we established a facile synthetic route by optimizing the reaction parameters, especially altering the effective concentration of the reducing agent, to influence their optical characteristics. The improvement of the photoluminescence intensity and superior colloidal stability was modeled from a theoretical standpoint. Moreover, the as-synthesized Cu NCs showed a significant reduction of toxicity in both in vitro and in vivo models. The possibility of using such Cu NCs as a diagnostic probe toward C. elegans was explored. Also, the extension of our approach toward improving the photoluminescence intensity of the Cu NCs on other ligand systems was demonstrated.
Stereoselective Addition of Alkynes to Ketenimines: Copper/Amine Catalyzed Sulfonyl Azide-Alkyne Cycloaddition Reactions for the Synthesis of (Z)-1,3-Enynes
Pothikumar R., Sivaraj C., Giridharan K., Ravva M.K., Namitharan K.
Article, Organic Letters, 2022, DOI Link
View abstract ⏷
Herein, we report a copper/amine catalyzed stereoselective addition of alkynes to ketenimine intermediates generated in situ from the sulfonyl azide-alkyne cycloaddition cascade for the stereoselective synthesis of (Z)-1,3-enynes. Significantly, for the first-time, enamine intermediates generated in the copper-catalyzed sulfonyl azide-alkyne cycloaddition reactions have been successfully trapped and isolated as the products. Density functional theory computations have also been performed and found to be consistent with the observed experimental stereoselectivity.
Theoretical insights into molecular design of hot-exciton based thermally activated delayed fluorescence molecules
Article, Materials Advances, 2022, DOI Link
View abstract ⏷
Despite the recent breakthroughs in the TADF process, more research is needed to understand its mechanism and develop rational molecular designs for structures with higher efficiencies and quantum yield. Hot exciton-based TADF materials, like traditional (cold) TADF, can effectively utilize singlet and triplet excitons, theoretically resulting in 100% IQE. However, in contrast to cold TADF (from low-lying T1 to S1), the RISC process in hot TADF occurs from high-lying triplet to singlet excited states (from Tm(m > 1) to Sn(n > 1)). However, designing materials that satisfy conditions for hot exciton formation, such as large triplet spacing in lower states and a small singlet-triplet gap in higher states, remains a difficult job. In this study, we explore and analyze the fundamental concepts of molecular design and suggest a design strategy by establishing structure-property relationships for hot-TADF molecules using density functional theory methods. This study could lead to new insights into molecular design approaches for organic materials with many hot exciton channels, which could lead to better exciton utilization.
Simultaneous interaction of graphene nanoflakes with cations and anions: A cooperativity study
Rudharachari Maiyelvaganan K., Prakash M., Kumar Ravva M.
Article, Computational and Theoretical Chemistry, 2022, DOI Link
View abstract ⏷
We have investigated the structure and the stability of ternary complexes, made up of an extended aromatic π-surface that simultaneously interacts with cation and anion on the opposite faces of the aromatic π-cloud. To understand the influence of the role of aromatic surfaces in the ternary complexes, we have considered various linear and circular polycyclic aromatic hydrocarbons (PAHs) as model systems for the extended π-electron surface. The interplay between the structure, stability, and cooperativity is studied using density functional theory (DFT) methods. Furthermore, the nature of the interaction, energetics, and origin of cooperative effects in the ternary complexes are characterized by using atoms in molecules (AIM), nucleus independent chemical shift (NICS), and energy decomposition analyses (EDA). Results obtained from these calculations unravel the cooperative effects present in the ternary complexes and the interplay between cation···π and anion···π interactions when they coexist in the same system.
A novel class of rigid-rod perylene diimides and isoindigo semiconducting polymers
Yu Y., Zhu D., Zhu X., Ravva M.K., Duan J., Jiang L., Li Z., Yue W.
Article, Polymer Chemistry, 2022, DOI Link
View abstract ⏷
Rigid-rod conjugated polymers contain only double-bond linkers instead of single bonds between the monomer linkages along the backbone. These polymers exhibit exceptional optoelectronic properties and promising device performances owing to their unique structures. Yet, such polymers are still very limited and little is known about their structure-property relationship so far. Herein, we have designed and synthesized a series of novel rigid-rod semiconducting polymers containing fused electron-deficient perylene diimides and isoindigo units through an inexpensive and high atom-economy method. Furthermore, the acid-mediated aldol condensation reactions do not involve any toxic reagents or transition metal catalysts. Most importantly, these polymers are isomerically pure unlike previously reported PDI polymers. The energy levels and optoelectronic properties of these polymers are tuned via adopting a molecular strategy of acene size optimization and heteroatom substitution on the variable lactone or lactams. All electron-deficient character endowed them with low-lying LUMOs, and electron transport in solution-processed thin film transistor devices has been realized using two of the polymers. Therefore the rigid-rod and fused semiconducting polymers reported here extend the scope of aldol polymerization and provide a remarkable platform for fundamental optoelectronic investigations and material innovation in the area of organic (bio)electronics.
Studies on hydrogen storage in molecules, cages, clusters, and materials: A DFT study
Maiyelvaganan K.R., Janani M., Gopalsamy K., Ravva M.K., Prakash M., Subramanian V.
Book chapter, Atomic Clusters with Unusual Structure, Bonding and Reactivity: Theoretical Approaches, Computational Assessment and Applications, 2022, DOI Link
View abstract ⏷
The inadequate fossil fuel resources and their impacts on the global environment are the reason for the inclination of researchers to improve clean energy technologies. Using fuel cells, the chemical energy can directly transform into electrical energy with high efficacy. Hydrogen is the most ensuring alternative for fossil fuel, but its storage is a prime issue. This chapter overviews hydrogen storage studies on a series of molecules, cages, and clusters. We describe how the nature of binding between hydrogen molecule and storage materials impact the absorption and desorption properties. We then discuss explicit examples of various hydrogen storage materials and their hydrogen storage capacities.
Synthesis ofortho-arylated and alkenylated benzamides by palladium-catalyzed denitrogenative cross-coupling reactions of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acids
Balakrishnan M.H., Kanagaraj M., Sankar V., Ravva M.K., Mannathan S.
Article, New Journal of Chemistry, 2021, DOI Link
View abstract ⏷
An efficient palladium-catalyzed denitrogenative Suzuki-Miyaura type cross-coupling of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acid is described. The reaction is compatible with various aryl and alkenyl boronic acids affordingortho-arylated and alkenylated benzamides in good to high yields. Heteroaromatic boronic acids were also successfully employed. Along with this, a coupling reaction was established by using phenyl boronate ester as the coupling partner. The reaction is believed to proceedviaa five-membered aza-palladacyclic intermediate. DFT calculations were studied comparing the reactivity of palladium and nickel complexes in the five-membered aza-metallacycle formation from 1,2,3-benzotriazin-4(3H)-ones. The application of the reaction was successfully demonstrated by convertingortho-alkenylated products toortho-alkylated products in high yieldsviaa reduction reaction.
Effect of both structural and electronic confinements on interaction, chemical reactivity and properties
Ravva M.K., Pawar R., Panneer S.V.K., Choutipalli V.S.K., Subramanian V.
Book chapter, Chemical Reactivity in Confined Systems: Theory, Modelling and Applications, 2021, DOI Link
View abstract ⏷
Particle in a box is a classic example of quantization through confinement. In the literature, many theoretical studies have been reported regarding the application of confinement models with hard and soft boundaries on a wide range of systems with different shapes and sizes. The n-electron delocalization on the surface of fullerene and sphere-like shape of fullerene offers a non-polar spherical confinement. Schlegel and co-workers have also studied the effect of confinement on chemical reactions by considering carbon nanotube (CNT) of different diameter using hybrid density functional theory. Systematic comparison of reaction energies in the gas phase and inside nanotube reveals that the energy barriers inside the tube are higher than the gas phase. The main reason for the high-energy barrier inside nanotube is due to the presence of nanotube confinement.
Theoretical Study on Understanding the Effects of Core Structure and Energy Level Tuning on Efficiency of Nonfullerene Acceptors in Organic Solar Cells
Joseph S., Ravva M.K., Davis B.A., Thomas S., Kalarikkal N.
Article, Advanced Theory and Simulations, 2021, DOI Link
View abstract ⏷
Nonfullerene acceptors (NFAs) are a new focus in organic photovoltaics (OPVs), and continue to progress upon the drawbacks of many fullerene-based electron acceptors. The aim of this work is to identify some important parameters that influence the efficiency of NF-acceptors in OPVs. These results provide an enhanced understanding of the effect of the NFAs core structure (electron rich/poor group) on the photophysical and optoelectronic properties. In addition, the effect of the small ΔLUMO value (the subtle difference in energy between LUMO+1 and LUMO orbitals of NFAs; LUMO=lowest unoccupied molecular orbitals) on ultrafast charge transfer and charge separation processes in OPVs, recently identified as a key factor for all top rated high performing NFAs, is studied. So far, ΔLUMO-based theoretical studies are limited to individual NFAs; here, for the first time, the authors have extended to the respective donor/acceptor complexes as well. Finally, based on the first-principles density functional theory calculations with the seven reported NFAs, (Formula presented.), P3HT, and the seven newly modeled donor–acceptor complexes, this study sheds light on important factors that will provide trends and guidelines for further rational design of more efficient NF-acceptors for OPVs.
Harnessing the Extracellular Electron Transfer Capability of Geobacter sulfurreducens for Ambient Synthesis of Stable Bifunctional Single-Atom Electrocatalyst for Water Splitting
Pedireddy S., Jimenez-Sandoval R., Ravva M.K., Nayak C., Anjum D.H., Jha S.N., Katuri K.P., Saikaly P.E.
Article, Advanced Functional Materials, 2021, DOI Link
View abstract ⏷
Single-atom metal (SA-M) catalysts with high dispersion of active metal sites allow maximum atomic utilization. Conventional synthesis of SA-M catalysts involves high-temperature treatments, leading to low yield with a random distribution of atoms. Herein, a nature-based facile method to synthesize SA-M catalysts (M = Fe, Ir, Pt, Ru, Cu, or Pd) in a single step at ambient temperature, using the extracellular electron transfer capability of Geobacter sulfurreducens (GS), is presented. Interestingly, the SA-M is coordinated to three nitrogen atoms adopting an MN3 on the surface of GS. Dry samples of SA-Ir@GS without further heat treatment show exceptionally high activity for oxygen evolution reaction when compared to benchmark IrO2 catalyst and comparable hydrogen evolution reaction activity to commercial 10 wt% Pt/C. The SA-Ir@GS exhibits the best water-splitting performance compared to other SA-M@GS, showing a low applied potential of 1.65 V to achieve 10 mA cm−2 in 1.0 M KOH with cycling over 5 h. The density functional calculations reveal that the large adsorption energy of H2O and moderate adsorption energies of reactants and reaction intermediates for SA-Ir@GS favorably improve its activity. This synthesis method at room temperature provides a versatile platform for the preparation of SA-M catalysts for various applications by merely altering the metal precursors.
Insights into the Ground-State Charge Transfer in Conjugated Polymer Donor–Acceptor Complexes
Article, Journal of Electronic Materials, 2021, DOI Link
View abstract ⏷
Van der Waals type forces are generally responsible for the stability of conjugated polymer–acceptor complexes, and no charge transfer is observed in the ground state. Electron transfer generally occurs from donor materials to acceptor materials via photoinduced electron transfer. Here, we report a partial ground-state charge transfer in the all-polymer donor–acceptor interface using density functional theory-based methods such as long-range corrected ωB97XD and hybrid meta exchange–correlation M06 functionals. These methods are also used to evaluate the geometrical and electronic properties of conjugated polymers in the neutral and charged states.
Effect of Alkoxy Side-Chains on Conjugated Polymer/Non-fullerene Acceptor Interfaces in Organic Solar Cells
Article, Journal of Electronic Materials, 2021, DOI Link
View abstract ⏷
In this study, we have attempted to gain insights into the impact of alkoxy side-chains substituted on the end group of the non-fullerene acceptor. It has been shown by experimental studies that the length and position of these alkoxy side-chains substantially influence the power conversion efficiencies of solar cell devices. A detailed analysis has been made on how the length of the alkoxy side-chains impact the molecular packing and electronic and optical properties of conjugated polymers and non-fullerene acceptor blends using quantum chemical methods. The results obtained from this study provide information on why a particular alkoxy side-chain results in better device efficiencies.
Fused ambipolar aza-isoindigos with NIR absorption
Yao L., Zhu D., Liao H., Haseena S., Ravva M.K., Cong S., Lan L., Wang Y., Li Z., Jiang L., Yue W.
Article, Organic Chemistry Frontiers, 2021, DOI Link
View abstract ⏷
Due to their advantages of being low-cost and light weight, and having mechanical flexibility, great attention has been focused on π-conjugated organic semiconductors. Many high-performing materials have been developed in the past decade. However, constructing electron-deficient ladder-type conjugated systems is far more challenging than constructing electron-rich systems. We have successfully synthesized a series of larger and extended novel electron-deficient aza-isoindigos (AIID-12, FAIID-12, and AIID-14) with up to 14 rings. Terminal fluorine atoms and the fusion of an additional naphthalene ring are also introduced to compare the properties of the resulting compounds to those of phenyl aza-isoindigos. Compared with isoindigo, the absorption spectra of AIID-12, FAIID-12, and AIID-14 extend into the NIR region at 900 nm due to their extended conjugation systems. These fused aza-isoindigo conjugated systems exhibit excellent solubility, highly planar backbones, substantial crystallinity, tunable conjugation lengths, and optoelectrical properties. The more extensive conjugated system with higher highest occupied molecular orbital (HOMO) and unchanged lowest unoccupied molecular orbital (LUMO) energy levels shows a narrow band gap and near-infrared absorption. Thus, the enhanced electron affinities (EAs) can facilitate the realization of electron-transport properties. As a result, OTFT devices based on AIID-14 exhibit a hole mobility of 0.076 cm2 V-1 s-1 and electron mobility of 0.003 cm2 V-1 s-1. Our results demonstrate the great potential of these aza-isoindigo systems for small-molecule semiconductor use. This journal is
Novel and asymmetric S,N-heterocyclics with fused six-membered rings for organic field effect transistor applications
Liao H., Chen M., Sun J., Haseena S., Ravva M.K., Xiao C., Zhang L., Wang Y., Li Z., Yue W.
Article, Journal of Materials Chemistry C, 2020, DOI Link
View abstract ⏷
We herein describe the design, synthesis, characterization and property evaluation of three novel π-conjugated ladder-type and asymmetric S,N-heterocyclics with fused six-membered rings. The unique molecular design incorporates electron-deficient pyrazine and electron-donating thienothiophene in one molecular skeleton to achieve fused and asymmetric heterocyclics with six consecutive rings, and we tuned the molecular structure with different alkyl chains and the ending chlorine substitution. Single-crystal structure studies and analysis of opto-electronic properties were carried out to understand the structure-property relationships for applying these π-scaffolds in organic single-crystal transistors. Charge mobility studies reveal a promising hole mobility of 0.64 cm2 V-1 s-1 for one of the asymmetric S,N-heterocyclics.
Effect of halogenated substituent on the properties of aza-octacenes
Luo Y., Yao L., Gu W., Xiao C., Liao H., Ravva M.K., Wang Y., Li Z., Zhang L., Lv A., Yue W.
Article, Organic Electronics, 2020, DOI Link
View abstract ⏷
We systematically designed and developed three novel halogenated aza-octacene derivatives, which have the same π-conjugated backbone with different terminal halogen groups (F, Cl, Br). These aza-octacene derivatives are synthesized by acid-catalyzed condensation of naphthalene-bisisatin with 4,5-dihalo-1,2-phenylenediamine. The in-depth experimental and theoretical analyses on these molecules, using the non-halogenated system as a reference, allowed us to understand the impact of halogenation on electronic and optical properties. Both electronic affinity (EA) and ionization potential (IP) are increased through peripheral halogen substitution. Chlorination enhances the EA more effectively compared with fluorination and bromination. Micro-crystal devices based on the bromine substituted aza-octacene derivative show only p-type charge transport behavior. In contrast, the chlorinated and the fluorinated aza-octacene derivatives exhibit ambipolar charge transport.
Benchmark studies on protonated benzene (BZH+) and water (W n, n = 1–6) clusters: a comparison of hybrid DFT with MP2/CBS and CCSD(T)/CBS methods
Maiyelvaganan K.R., Ravva M.K., Prakash M., Subramanian V.
Article, Theoretical Chemistry Accounts, 2020, DOI Link
View abstract ⏷
The selection of a suitable density functional theory (DFT) method is critical to study the interfacial interactions between the protonated species and water clusters at the carbon surface. The interfacial interactions are crucial for the stability of complexes with the support of various kinds of noncovalent interactions. To model this environment, we consider excess proton with benzene [i.e., protonated benzene (BZH+)] and water clusters using high-level electronic structure calculations. These clusters were stabilized by different kinds of noncovalent interactions at the interface. Modeling these clusters is challenging as high-level electronic structure calculations are expensive, whereas less expensive DFT-based methods are inconsistent. Thus, in the present study, we have chosen various hybrid DFT functionals (such as B3LYP, PBE0, M05-2X, M06-2X, and M11) to study the geometries, energetics, and the importance of interfacial interactions. Furthermore, these methods performance is validated by using MP2/CBS and CCSD(T)/CBS approaches. It is found that the selected functionals are reliable to predict the structure, but the energetics of these clusters are varied. Also, each one of these methods has its own advantage in certain aspects. Scrutiny of result reveals that hybrid GGA (PBE0) and hybridmeta-GGA (M11) functionals are more consistent for the structure and stability with the benchmark obtained from MP2/CBS and CCSD(T)/CBS approaches. Besides, our benchmark report states that the selected DFT method can be suitable for the following individual interactions; (1) PBE0 suited for O–H+···O, O–H+···π and C–H+···O interactions, (2) M05-2X more suited for O–H···π, C–H···O, and (3) B3LYP method highly favor for the O–H+···O interactions (i.e., proton transfer). Overall, PBE0/aVTZ method has an excellent correlation with MP2/CBS and CCSD(T)/CBS methods based on our analysis using the mean signed error and correlation coefficient (r) analyses.
A Novel Mitigation Mechanism for Photo-Induced Trapping in an Anthradithiophene Derivative Using Additives
Nasrallah I., Ravva M.K., Broch K., Novak J., Armitage J., Schweicher G., Sadhanala A., Anthony J.E., Bredas J.-L., Sirringhaus H.
Article, Advanced Electronic Materials, 2020, DOI Link
View abstract ⏷
A novel trap mitigation mechanism using molecular additives, which relieves a characteristic early turn-on voltage in a high-mobility p-type acene-based small-molecule organic semiconductor, when processed from hydrous solvents, is reported. The early turn-on voltage is attributed to photo-induced trapping, and additive incorporation is found to be very effective in suppressing this effect. Remarkably, the molecular additive does not disturb the charge transport properties of the small-molecule semiconductor, but rather intercalates in the crystal structure. This novel technique allows for the solution-processing of small molecular semiconductors from hydrous solvents, greatly simplifying manufacturing processes for large-area electronics. Along with various electric and spectroscopic characterization techniques, simulations have given a deeper insight into the trap mitigation effect induced by the additive.
Metal-free polymerization: Synthesis and properties of fused benzo[1,2-: B:4,5-b ′]bis [b] benzothiophene (BBBT) polymers
Yao L., Liao H., Ravva M.K., Guo Y., Duan J., Wang Y., Yu Y., Li Z., McCulloch I., Yue W.
Article, Polymer Chemistry, 2020, DOI Link
View abstract ⏷
We report the "green" synthesis and characterization of a series of fused benzo[1,2-b:4,5-b′]bis[b]benzothiophene (BBBT) polymers containing a phenyl ring and naphthalene as comonomers, as well as BBBT homopolymers. These novel fused polymers have been obtained from simple acid and hexaethyltriaminophosphine catalyzed polymerization without involving any metal catalyst. The effect of the different aromatic units on the optical and electronic properties of the resulting polymers has been studied. It was found that these polymers possess high electron affinities due to the presence of electron-deficient lactams on each repeat unit. BBBT-P and BBBT-N exhibit NIR absorption spectra with the tail extending to 1000 nm, while the BBBT homopolymer exhibits a large blue-shifted absorption.
Blue LED Mediated Intramolecular C-H Functionalization and Cyclopropanation of Tryptamines: Synthesis of Azepino[4, 5-b]indoles and Natural Product Inspired Polycyclic Indoles
Chauhan J., Ravva M.K., Gremaud L., Sen S.
Article, Organic Letters, 2020, DOI Link
View abstract ⏷
We report a novel blue LED mediated intramolecular C-H functionalization of tryptamine derivatives to generate azepino[4, 5-b]indoles (4) in moderate to good yields. By altering the substitution at the tryptamine nitrogen, intramolecular cyclopropanation is achieved in high yields under the same reactions condition to provide natural product inspired polycyclic indoles (6), which are further transformed to spiropiperidino (5 and 8) indoles in decent yields. The mechanism of formation of the compounds was investigated through DFT studies.
Twisted Eigen Can Induce Proton Transfer at a Hydrophobic-Hydrophilic Interface
Maiyelvaganan K.R., Ravva M.K., Prakash M.
Article, Journal of Physical Chemistry A, 2020, DOI Link
View abstract ⏷
The investigation of proton localization at a hydrophobic-hydrophilic interface is an important problem in chemical and materials sciences. In this study, protonated benzene (i.e., benzenium ion) and water clusters [BZH+Wn (where n = 1-6)] are selected as prototype models to understand the interfacial interactions and proton transfer mechanism between a carbonaceous surface and water molecules. The excess protons can localize in the vicinity of the hydrophobic-hydrophilic interface, and these clusters are stabilized by various kinds of noncovalent interactions. Calculations are carried out using ab initio (MP2) and density functional theory B3LYP methods to shed more light on geometries, energetics, and spectral signatures of the protonated species [H+(H2O)n] at the interfaces. These calculations revealed few low-lying isomers, which have not been reported earlier. Scrutiny of the results reveals that proton localization in the hydrophilic environment is more stable than the hydrophobic benzene π-cloud. Furthermore, the occurrence of an O-H+···πhydrogen bond significantly influences the O-H+···O interactions in the water clusters and also intensively affects the vibrational modes of the Eigen cation. Thus, the aromatic π-clouds can stabilize the Eigen cation and at the same time, a twisted form of Eigen (one O-H+···π→ two O-H+···π) can enhance the proton transfer through the water chain via a Grotthuss-type mechanism. The vibrational spectra of these clusters reveal that there is a large red-shifted frequency for the O-H+···O, O-H+···π, and O-H···πmodes of interaction. The energetic values and vibrational frequencies obtained from the B3LYP method are in close agreement with the MP2 level and experimental values, respectively.
Interactions of thiol and alkoxy radical with coinage metal nanoclusters
Haseena S., Kumar R.M., Rajapandian V., Subramanian V.
Article, Applied Surface Science, 2019, DOI Link
View abstract ⏷
Interaction of small neutral coinage metal clusters (M19 = Ag19/Au19) with thiol/alkoxy radical (E = -SCH3, -OCH3, and -OCH2CH3) has been investigated to understand the bonding mechanism in the coinage metal−molecule junctions, which would allow to design biocompatible materials. In this study, structure, reactivity, and energy decomposition analysis (EDA) of M19−E complexes have been unravelled using density functional theory (DFT) based Perdew, Burke and Ernzerhof (PBE) method. In addition, the theory of “atoms in molecules” (AIM) has also been used characterize the nature of interaction. The calculated reactivity descriptors predict that the vertex atoms (Ag/Au) are the most reactive site for nucleophilic attack. The atoms lying at the center of each face are favourable for an electrophilic attack in both the cases. Geometrical parameters illustrate that the structure of the molecules change significantly before and after interactions. The signatures of ∇2ρ(r) and Hc for the anchoring bonds are respectively positive and negative, revealing that these bonds are partially electrostatic and covalent in nature. EDA calculation indicates that the largest contribution to the M−X (X = O/S) bond arise from ΔEorb and ΔEelstat contributions. Specifically, contribution from the orbital interaction is higher than the electrostatic contribution, which further confirms the covalent nature of the interaction.
Fused Pyrazine- and Carbazole-Containing Azaacenes: Synthesis and Properties
Liao H., Xiao C., Ravva M.K., Yao L., Yu Y., Yang Y., Zhang W., Zhang L., Li Z., McCulloch I., Yue W.
Article, ChemPlusChem, 2019, DOI Link
View abstract ⏷
A new family of azaacenes has been designed and synthesized by incorporating the electron-withdrawing sp2-hybridized nitrogen of pyrazine and electron-donating nitrogen of carbazole in a molecular skeleton. Two different conjugated lengths of 8-ring aza-nonacene and 10-ring aza-undecene have been achieved by an efficient condensation reaction. The unique optoelectronic properties of these molecules were investigated using both experimental and theoretical techniques. The azaacenes show visible-region absorption and near-infrared (NIR) fluorescence. These compounds can serve as hole-transport semiconductors for solution-processed organic field-effect transistors (OFETs). Single-crystal transistor devices of one of the aza-nonacenes exhibit hole charge transport behavior with a hole mobility of 0.07 cm2/Vs and an on/off current ratio of 1.3x106.
The synthesis and properties of a new class of π-expanded diketopyrrolopyrrole analogs and conjugated polymers
Wang Y., Xu Y., Ravva M.K., Yu Y., Xiao M., Xue X., Yang X., Chen Y., Li Z., Yue W.
Article, Organic Chemistry Frontiers, 2019, DOI Link
View abstract ⏷
A novel 6-5-5-5 ring containing mono-ketopyrrole in its fully conjugated state, resembling a π-expanded diketopyrrolopyrrole analog, has been designed and synthesized. The new type of molecule shows intense visible range absorption and a reversible reduction potential. Further, this class of molecule can be incorporated into a family of alternative conjugated polymers. These new polymers possess planar backbones due to the fused π-expanded diketopyrrolopyrrole analog building block and smaller steric effects between the thiophene of azaanthracene and the flanking thiophene rings of the comonomer units. These new very low band gap polymers exhibit NIR absorption spectra that are extended to 1200 nm due to the extended effective conjugation length and increased molecular orbital overlap between aromatic monomer units. Our results demonstrate that these π-expanded diketopyrrolopyrrole analogs could be a useful building block for semiconducting polymers.
Harnessing Autoxidation of Aldehydes: In Situ Iodoarene Catalyzed Synthesis of Substituted 1,3,4-Oxadiazole, in the Presence of Molecular Oxygen
Article, Organic Letters, 2019, DOI Link
View abstract ⏷
Isobutyraldehyde underwent auto-oxidation in the presence of molecular oxygen to generate an acyloxy radical under a "metal-free" environment. They were subsequently exploited in situ to afford hypervalent iodines with p-anisolyl iodide which generated substituted 1,3,4-oxadiazoles in moderate to excellent yields from N′-arylidene acetohydrazides. The reaction strategy tolerated diverse substitution on the hydrazide substrates. Control experiments and literature precedence supported the formation of an in situ iodosylarene complex that facilitates the formation of products.
Directing-group-assisted manganese-catalyzed cyclopropanation of indoles
Dutta P.K., Chauhan J., Ravva M.K., Sen S.
Article, Organic Letters, 2019, DOI Link
View abstract ⏷
The first manganese-catalyzed cyclopropanation of indoles is reported in moderate to excellent yield with methyl-2-diazo-2-arylacetates. This new strategy involved acetyl (COCH 3 ) as the directing group and exhibited exceptional functional group tolerance. In the absence of stereodirecting groups the desired products were obtained as a mixture of diastereomers (7:3 → 8:2). Control experiments and DFT studies elucidated the probable pathway for the formation of cyclopropane-fused indole product. Deacetylation of the final products afforded both C3-substituted NH-indoles.
Cobalt-Catalyzed, Hydroxyl-Assisted C-H Bond Functionalization: Access to Diversely Substituted Polycyclic Pyrans
Article, Journal of Organic Chemistry, 2019, DOI Link
View abstract ⏷
Highly efficient oxidative annulation of alkynes furnished diversely substituted pyran[2,3,4-de]chromene-2-one derivatives and related polycycles in moderate to high yield. The reaction is catalyzed by nontoxic, air-stable, and inexpensive Cp∗Co(CO)I 2 catalyst. The hydroxyl moiety at the substrate acts as the directing group for the C-H bond activation.
Charge and Triplet Exciton Generation in Neat PC70BM Films and Hybrid CuSCN:PC70BM Solar Cells
Karuthedath S., Gorenflot J., Firdaus Y., Sit W.-Y., Eisner F., Seitkhan A., Ravva M.K., Anthopoulos T.D., Laquai F.
Article, Advanced Energy Materials, 2019, DOI Link
View abstract ⏷
Organic solar cells that use only fullerenes as the photoactive material exhibit poor exciton-to-charge conversion efficiencies, resulting in low internal quantum efficiencies (IQE). However, the IQE can be greatly improved, when copper(I) thiocyanate (CuSCN) is used as a carrier-selective interlayer between the phenyl-C70-butyric acid methyl ester (PC70BM) layer and the anode. Efficiencies of ≈5.4% have recently been reported for optimized CuSCN:PC70BM (1:3)-mesostructured heterojunctions, yet the reasons causing the efficiency boost remain unclear. Here, transient absorption (TA) spectroscopy is used to demonstrate that CuSCN does not only act as a carrier-selective electrode layer, but also facilitates fullerene exciton dissociation and hole transfer at the interface with PC70BM. While intrinsic charge generation in neat PC70BM films proceeds with low yield, hybrid films exhibit much improved exciton dissociation due to the presence of abundant interfaces. Triplet generation with a rate proportional to the product of singlet and charge concentrations is observed in neat PC70BM films, implying a charge–singlet spin exchange mechanism, while in hybrid films, this mechanism is absent and triplet formation is a consequence of nongeminate recombination of free charges. At low carrier concentrations, the fraction of charges outweighs the population of triplets, leading to respectable device efficiencies under one sun illumination.
Effect of conjugation length on the properties of fused perylene diimides with variable isoindigos
Yu Y., Xue N., Xiao C., Ravva M.K., Guo Y., Wu L., Zhang L., Li Z., Yue W., Wang Z.
Article, Journal of Materials Chemistry C, 2019, DOI Link
View abstract ⏷
We have successfully synthesized four fused hybrid diimide and diamide arrays with different effective conjugation lengths of perylene diimides and isoindigos. These arrays with varying numbers of amides and imides are an efficient strategy to fine-tune the opto-electronic properties, conformation, energy levels and device performance. It is shown that additional fused isoindigos lead to much lower electron affinity with no influence on the ionic potential. The impact of adding different additional central electron deficient isoindigos to the fused arrays has also been investigated systemically. PDI-BDOPV-PDI incorporating a strong electron deficient BDOPV unit with enforced coplanarity exhibits a very low lowest unoccupied molecular orbital (LUMO) level of -4.11 eV, and the absorption spectrum of PDI-DPN-PDI was even extended to 1000 nm. Thin film transistors were fabricated with these arrays as the semiconductor layers, the fused arrays display electron transport behaviors.
Copper-Catalyzed Ring-Expansion Cascade of Azirines with Alkynes: Synthesis of Multisubstituted Pyridines at Room Temperature
Article, Organic Letters, 2018, DOI Link
View abstract ⏷
The first intermolecular ring-expansion cascade of azirines with alkynes for the synthesis of pyridines, enabled by a copper/triethylamine catalytic system via simultaneous generation and utilization of yne-enamine and skipped-yne-imine intermediates, is reported. Experimental as well as computational mechanistic studies revealed that the role of triethylamine is crucial in deciding the reaction pathway toward the pyridine products. This process offers a novel, one-step, direct, and practical strategy for the rapid construction of highly substituted pyridines under exceedingly mild conditions, and an installed alkyne functionality.
Fused electron deficient semiconducting polymers for air stable electron transport
Onwubiko A., Yue W., Jellett C., Xiao M., Chen H.-Y., Ravva M.K., Hanifi D.A., Knall A.-C., Purushothaman B., Nikolka M., Flores J.-C., Salleo A., Bredas J.-L., Sirringhaus H., Hayoz P., McCulloch I.
Article, Nature Communications, 2018, DOI Link
View abstract ⏷
Conventional semiconducting polymer synthesis typically involves transition metal-mediated coupling reactions that link aromatic units with single bonds along the backbone. Rotation around these bonds contributes to conformational and energetic disorder and therefore potentially limits charge delocalisation, whereas the use of transition metals presents difficulties for sustainability and application in biological environments. Here we show that a simple aldol condensation reaction can prepare polymers where double bonds lock-in a rigid backbone conformation, thus eliminating free rotation along the conjugated backbone. This polymerisation route requires neither organometallic monomers nor transition metal catalysts and offers a reliable design strategy to facilitate delocalisation of frontier molecular orbitals, elimination of energetic disorder arising from rotational torsion and allowing closer interchain electronic coupling. These characteristics are desirable for high charge carrier mobilities. Our polymers with a high electron affinity display long wavelength NIR absorption with air stable electron transport in solution processed organic thin film transistors.
Co-operativity in non-covalent interactions in ternary complexes: a comprehensive electronic structure theory based investigation
Panneer S.V.K., Ravva M.K., Mishra B.K., Subramanian V., Sathyamurthy N.
Article, Journal of Molecular Modeling, 2018, DOI Link
View abstract ⏷
The structure and stability of various ternary complexes in which an extended aromatic system such as coronene interacts with ions/atoms/molecules on opposite faces of the π-electron cloud were investigated using ab initio calculations. By characterizing the nature of the intermolecular interactions using an energy decomposition analysis, it was shown that there is an interplay between various types of interactions and that there are co-operativity effects, particularly when different types of interactions coexist in the same system. [Figure not available: see fulltext.].
Bulk Heterojunction Solar Cells: Impact of Minor Structural Modifications to the Polymer Backbone on the Polymer–Fullerene Mixing and Packing and on the Fullerene–Fullerene Connecting Network
Wang T., Chen X.-K., Ashokan A., Zheng Z., Ravva M.K., Bredas J.-L.
Article, Advanced Functional Materials, 2018, DOI Link
View abstract ⏷
The morphology of the active layer of a bulk heterojunction solar cell, made of a blend of an electron-donating polymer and an electron-accepting fullerene derivative, is known to play a determining role in device performance. Here, a combination of molecular dynamics simulations and long-range corrected density functional theory calculations is used to elucidate the molecular-scale effects that even minor structural changes to the polymer backbone can have on the “local” morphology; this study focuses on the extent of polymer–fullerene mixing, on their packing, and on the characteristics of the fullerene–fullerene connecting network in the mixed regions, aspects that are difficult to access experimentally. Three representative polymer donors are investigated: (i) poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophen-5,5′″-diyl)] (PffBT4T-2OD); (ii) poly[(2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophen-5,5′″-diyl)] (PBT4T-2OD), where the fluorine atoms in the benzothiadiazole moieties of PffBT4T-2OD are replaced with hydrogen atoms; and (iii) poly[(2,2′-bithiophene)-alt-(4,7-bis((2-decyltetradecyl)thiophen-2-yl)-5,6-difluoro-2-propyl-2H-benzo[d][1,2,3]triazole)] (PT2-FTAZ), where the sulfur atoms in the benzothiadiazole moieties of PffBT4T-2OD are replaced with nitrogen atoms carrying a linear C3H7 side-chain; these polymers are mixed with the phenyl-C71-butyric acid methyl ester (PC71BM) acceptor. This study also discusses the nature of the charge-transfer electronic states appearing at the donor–acceptor interfaces, the electronic couplings relevant for the charge-recombination process, and the electron-transfer features between neighboring PC71BM molecules.
Impact of solution temperature-dependent aggregation on the solid-state packing and electronic properties of polymers for organic photovoltaics
Ashokan A., Wang T., Ravva M.K., Bredas J.-L.
Article, Journal of Materials Chemistry C, 2018, DOI Link
View abstract ⏷
The performance of a bulk-heterojunction organic solar cell critically depends on the morphology of the active layer. The solution temperature-dependent aggregation characteristics of a series of polymer donors have been recently exploited as an effective protocol for morphology control in high-efficiency devices. Here, we use an approach combining molecular dynamics simulations and long-range corrected density functional theory calculations to investigate the impact of solution temperature-dependent aggregation on the polymer solid-state packing and electronic properties. We consider two representative polymer systems: (i) PffBT4T-2OD (poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′′′-di(2-octyldodecyl)-2,2′;5′,2′′;5′′,2′′′-quaterthiophen-5,5′′′-diyl)]), and (ii) PBT4T-2OD (poly[(2,1,3-benzothiadiazole-4,7-diyl)-alt-(3,3′′′-di(2-octyldodecyl)-2.2′;5′,2′′;5′′,2′′′-quarterthiophen-5,5′′′-diyl)]), where the fluorine atoms on the benzothiadiazole moieties of PffBT4T-2OD are replaced with hydrogen atoms. We find that both temperature-dependent aggregation and the presence of fluorine atoms are important in determining the nature of the solid-state packing and the electronic properties in the polymer phases. Our results are consistent with the experimental data that show that PffBT4T-2OD aggregates at lower temperatures and leads to higher OPV efficiency.
Synthesis and properties of isoindigo and benzo[1,2-: B:4,5-b ′]bis [b] benzothiophene oligomers
Liao H., Xiao C., Ravva M.K., Wang Y., Little M., Jenart M.V.C., Onwubiko A., Li Z., Wang Z., Bredas J.-L., McCulloch I., Yue W.
Article, Chemical Communications, 2018, DOI Link
View abstract ⏷
A well-defined series of long and soluble isoindigo thienoacene oligomers have been synthesized from a novel electron deficient building block: Benzo[1,2-b:4,5-b′]bis[b]benzothiophene bislactams. Extension of the π-conjugated systems facilitates control of the optical, electronic and device characteristics.
Charge-Transfer Dynamics in the Lowest Excited State of a Pentacene-Fullerene Complex: Implications for Organic Solar Cells
Joseph S., Ravva M.K., Bredas J.-L.
Article, Journal of Physical Chemistry Letters, 2017, DOI Link
View abstract ⏷
We characterize the dynamic nature of the lowest excited state in a pentacene/C60 complex on the femtosecond time scale, via a combination of ab initio molecular dynamics and time-dependent density functional theory. We analyze the correlations between the molecular vibrations of the complex and the oscillations in the electron-transfer character of its lowest excited state, which point to vibration-induced coherences between the (pentacene-based) local-excitation (LE) state and the complex charge-transfer (CT) state. We discuss the implications of our results on this model system for the exciton-dissociation process in organic solar cells.
Molecular Understanding of Fullerene – Electron Donor Interactions in Organic Solar Cells
Ryno S.M., Ravva M.K., Chen X., Li H., Bredas J.-L.
Review, Advanced Energy Materials, 2017, DOI Link
View abstract ⏷
Organic solar cells hold promise of providing low-cost, renewable power generation, with current devices providing up to 13% power conversion efficiency. The rational design of more performant systems requires an in-depth understanding of the interactions between the electron donating and electron accepting materials within the active layers of these devices. Here, we explore works that give insight into the intermolecular interactions between electron donors and electron acceptors, and the impact of molecular orientations and environment on these interactions. We highlight, from a theoretical standpoint, the effects of intermolecular interactions on the stability of charge carriers at the donor/acceptor interface and in the bulk and how these interactions influence the nature of the charge transfer states as well as the charge separation and charge transport processes.
High operational and environmental stability of high-mobility conjugated polymer field-effect transistors through the use of molecular additives
Nikolka M., Nasrallah I., Rose B., Ravva M.K., Broch K., Sadhanala A., Harkin D., Charmet J., Hurhangee M., Brown A., Illig S., Too P., Jongman J., McCulloch I., Bredas J.-L., Sirringhaus H.
Article, Nature Materials, 2017, DOI Link
View abstract ⏷
Due to their low-temperature processing properties and inherent mechanical flexibility, conjugated polymer field-effect transistors (FETs) are promising candidates for enabling flexible electronic circuits and displays. Much progress has been made on materials performance; however, there remain significant concerns about operational and environmental stability, particularly in the context of applications that require a very high level of threshold voltage stability, such as active-matrix addressing of organic light-emitting diode displays. Here, we investigate the physical mechanisms behind operational and environmental degradation of high-mobility, p-type polymer FETs and demonstrate an effective route to improve device stability. We show that water incorporated in nanometre-sized voids within the polymer microstructure is the key factor in charge trapping and device degradation. By inserting molecular additives that displace water from these voids, it is possible to increase the stability as well as uniformity to a high level sufficient for demanding industrial applications.
Computational methodologies for developing structure-morphology-performance relationships in organic solar cells: A protocol review
Do K., Ravva M.K., Wang T., Bredas J.-L.
Article, Chemistry of Materials, 2017, DOI Link
View abstract ⏷
We outline a step-by-step protocol that incorporates a number of theoretical and computational methodologies to evaluate the structural and electronic properties of π-conjugated semiconducting materials in the condensed phase. Our focus is on methodologies appropriate for the characterization, at the molecular level, of the morphology in blend systems consisting of an electron donor and electron acceptor, of importance for understanding the performance properties of bulk-heterojunction organic solar cells. The protocol is formulated as an introductory manual for investigators who aim to study the bulk-heterojunction morphology in molecular details, thereby facilitating the development of structure-morphology-property relationships when used in tandem with experimental results.
Noncovalent Interactions in Organic Electronic Materials
Ravva M.K., Risko C., Bredas J.-L.
Book chapter, Non-Covalent Interactions in Quantum Chemistry and Physics: Theory and Applications, 2017, DOI Link
View abstract ⏷
In this chapter, we provide an overview of how noncovalent interactions, determined by the chemical structure of π-conjugated molecules and polymers, govern essential aspects of the electronic, optical, and mechanical characteristics of organic semiconductors. We begin by describing general aspects of materials design, including the wide variety of chemistries exploited to control the electronic and optical properties of these materials. We then discuss explicit examples of how the study of noncovalent interactions can provide deeper chemical insights that can improve the design of new generations of organic electronic materials.
Structural variations to a donor polymer with low energy losses
Yuan J., Ran N.A., Ford M.J., Wang M., Ravva M.K., Mai C.-K., Liu X., Bredas J.-L., Nguyen T.-Q., Ma W., Bazan G.C.
Article, Journal of Materials Chemistry A, 2017, DOI Link
View abstract ⏷
Two regioregular narrow bandgap conjugated polymers with a D′-A-D-A repeat unit architecture, namely PIFCF and PSFCF, were designed and synthesized. Both polymers contain strictly organized fluorobenzo[c][1,2,5]thiadiazole (FBT) orientations and different solubilizing side chains for solution processing. Compared to the previously reported asymmetric pyridyl-[2,1,3]thiadiazole (PT) based regioregular polymer, namely PIPCP, PIFCF and PSFCF exhibit wider bandgaps, tighter π-π stacking, and improved hole mobilities. When incorporated into solar cells with fullerene acceptors, the Eloss = Eg - eVoc values of PIFCF and PSFCF devices are increased compared to solar cells based on PIPCP. Determination of Ect in these solar cells reveals that, relative to PIPCP, PIFCF solar cells lose more energy from Eg - Ect, and PSFCF solar cells lose more energy from both Eg - Ect and Ect - eVoc. The close structural relationship between PIPCP and PIFCF provides an excellent framework to establish molecular features that impact the relationship between Eg and Ect. Theoretical calculations predict that Eloss of PIFCF:PC61BM would be higher than in the case of PIPCP:PC61BM, due to greater Eg - Ect. These findings provide insight into the design of high performance, low voltage loss photovoltaic polymeric materials with desirable optoelectronic properties.
Limits for Recombination in a Low Energy Loss Organic Heterojunction
Menke S.M., Sadhanala A., Nikolka M., Ran N.A., Ravva M.K., Abdel-Azeim S., Stern H.L., Wang M., Sirringhaus H., Nguyen T.-Q., Bredas J.-L., Bazan G.C., Friend R.H.
Article, ACS Nano, 2016, DOI Link
View abstract ⏷
Donor-acceptor organic solar cells often show high quantum yields for charge collection, but relatively low open-circuit voltages (VOC) limit power conversion efficiencies to around 12%. We report here the behavior of a system, PIPCP:PC61BM, that exhibits very low electronic disorder (Urbach energy less than 27 meV), very high carrier mobilities in the blend (field-effect mobility for holes >10-2 cm2 V-1 s-1), and a very low driving energy for initial charge separation (50 meV). These characteristics should give excellent performance, and indeed, the VOC is high relative to the donor energy gap. However, we find the overall performance is limited by recombination, with formation of lower-lying triplet excitons on the donor accounting for 90% of the recombination. We find this is a bimolecular process that happens on time scales as short as 100 ps. Thus, although the absence of disorder and the associated high carrier mobility speeds up charge diffusion and extraction at the electrodes, which we measure as early as 1 ns, this also speeds up the recombination channel, giving overall a modest quantum yield of around 60%. We discuss strategies to remove the triplet exciton recombination channel.
Effect of Molecular Packing and Charge Delocalization on the Nonradiative Recombination of Charge-Transfer States in Organic Solar Cells
Chen X.-K., Ravva M.K., Li H., Ryno S.M., Bredas J.-L.
Article, Advanced Energy Materials, 2016, DOI Link
Nature of the binding interactions between conjugated polymer chains and fullerenes in bulk heterojunction organic solar cells
Ravva M.K., Wang T., Bredas J.-L.
Article, Chemistry of Materials, 2016, DOI Link
View abstract ⏷
Blends of π-conjugated polymers and fullerene derivatives are ubiquitous as the active layers of organic solar cells. However, a detailed understanding of the weak noncovalent interactions at the molecular level between the polymer chains and fullerenes is still lacking and could help in the design of more efficient photoactive layers. Here, using a combination of long-range corrected density functional theory calculations and molecular dynamic simulations, we report a thorough characterization of the nature of binding between fullerenes (C60 and PC61BM) and poly(benzo[1,2-b:4,5-b′]dithiophene-thieno[3,4-c]pyrrole-4,6-dione) (PBDTTPD) chains. We illustrate the variations in binding strength when the fullerenes dock on the electron-rich vs electron-poor units of the polymer as well as the importance of the role played by the polymer and fullerene side chains and the orientations of the PC61BM molecules with respect to the polymer backbones.
Impact of Fluorine Substituents on π-Conjugated Polymer Main-Chain Conformations, Packing, and Electronic Couplings
Do K., Saleem Q., Ravva M.K., Cruciani F., Kan Z., Wolf J., Hansen M.R., Beaujuge P.M., Bredas J.-L.
Article, Advanced Materials, 2016, DOI Link
Impact of the Nature of the Side-Chains on the Polymer-Fullerene Packing in the Mixed Regions of Bulk Heterojunction Solar Cells
Wang T., Ravva M.K., Bredas J.-L.
Article, Advanced Functional Materials, 2016, DOI Link
View abstract ⏷
Polymer-fullerene packing in mixed regions of a bulk heterojunction solar cell is expected to play a major role in exciton-dissociation, charge-separation, and charge-recombination processes. Here, molecular dynamics simulations are combined with density functional theory calculations to examine the impact of nature and location of polymer side-chains on the polymer-fullerene packing in mixed regions. The focus is on poly-benzo[1,2-b:4,5-b′]dithiophene-thieno[3,4-c]pyrrole-4,6-dione (PBDTTPD) as electron-donating material and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as electron-accepting material. Three polymer side-chain patterns are considered: i) linear side-chains on both benzodithiophene (BDT) and thienopyrroledione (TPD) moieties; ii) two linear side-chains on BDT and a branched side-chain on TPD; and iii) two branched side-chains on BDT and a linear side-chain on TPD. Increasing the number of branched side-chains is found to decrease the polymer packing density and thereby to enhance PBDTTPD–PC61 BM mixing. The nature and location of side-chains are found to play a determining role in the probability of finding PC61BM molecules close to either BDT or TPD. The electronic couplings relevant for the exciton-dissociation and charge-recombination processes are also evaluated. Overall, the findings are consistent with the experimental evolution of the PBDTTPD–PC61BM solar-cell performance as a function of side-chain patterns.
Effect of Substituents on the Electronic Structure and Degradation Process in Carbazole Derivatives for Blue OLED Host Materials
Hong M., Ravva M.K., Winget P., Bredas J.-L.
Article, Chemistry of Materials, 2016, DOI Link
View abstract ⏷
We investigate the dissociation mechanism of the C-N bond between carbazole and dibenzothiophene in carbazole-dibenzothiophene (Cz-DBT) positional isomers, selected as representative systems for blue host materials in organic light-emitting diodes (OLEDs). The C-N bond dissociation energies, calculated at the density functional theory level, are found to depend strongly on the charge states of the parental molecules. In particular, the anionic C-N bond dissociations resulting in a carbazole anion can have low dissociation energies (∼1.6 eV) with respect to blue emission energy. These low values are attributed to the large electron affinity of the carbazole radical, a feature that importantly can be modulated via substitution. Substitution also impacts the energies of the first excited electronic states of the Cz-DBT molecules since these states have an intramolecular charge-transfer nature due to the spatially localized character of the frontier molecular orbitals within the carbazole moiety (for the HOMO) and the dibenzothiophene moiety (for the LUMO). The implications of these results must be considered when designing blue OLED hosts since these materials must combine chemical stability and high triplet energy.
Ionization Energies, Electron Affinities, and Polarization Energies of Organic Molecular Crystals: Quantitative Estimations from a Polarizable Continuum Model (PCM)-Tuned Range-Separated Density Functional Approach
Sun H., Ryno S., Zhong C., Ravva M.K., Sun Z., Korzdorfer T., Bredas J.-L.
Article, Journal of Chemical Theory and Computation, 2016, DOI Link
View abstract ⏷
We propose a new methodology for the first-principles description of the electronic properties relevant for charge transport in organic molecular crystals. This methodology, which is based on the combination of a nonempirical, optimally tuned range-separated hybrid functional with the polarizable continuum model, is applied to a series of eight representative molecular semiconductor crystals. We show that it provides ionization energies, electron affinities, and transport gaps in very good agreement with experimental values, as well as with the results of many-body perturbation theory within the GW approximation at a fraction of the computational costs. Hence, this approach represents an easily applicable and computationally efficient tool to estimate the gas-to-crystal phase shifts of the frontier-orbital quasiparticle energies in organic electronic materials.
Benchmarking Density Functional Theory Approaches for the Description of Symmetry Breaking in Long Polymethine Dyes
Gieseking R.L., Ravva M.K., Coropceanu V., Bredas J.-L.
Article, Journal of Physical Chemistry C, 2016, DOI Link
View abstract ⏷
Long polymethines are well-known experimentally to symmetry-break, which dramatically modifies their linear and nonlinear optical properties. Computational modeling could be very useful to provide insight into the symmetry-breaking process, which is not readily available experimentally; however, accurately predicting the crossover point from symmetric to symmetry-broken structures has proven challenging. Here, we benchmark the accuracy of several density functional theory approaches relative to CCSD(T) geometries. In particular, we compare analogous hybrid and long-range-corrected (LRC) functionals to clearly show the influence of the functional exchange term. Although both hybrid and LRC functionals can be tuned to reproduce the CCSD(T) geometries, the LRC functionals are better performing at reproducing the geometry evolution with chain length and provide a finite upper limit for the gas-phase crossover point; these methods also provide good agreement with the experimental crossover points for more complex polymethines in polar solvents. Using an approach based on LRC functionals, a reduction in the crossover length is found with increasing medium dielectric constant, which is related to localization of the excess charge on the end groups. Symmetry breaking is associated with the appearance of an imaginary frequency of b2 symmetry involving a large change in the degree of bond-length alternation. Examination of the IR spectra shows that short, isolated streptocyanines have a mode at ?1200 cm-1 involving a large change in bond-length alternation; as the polymethine length or the medium dielectric increases, the frequency of this mode decreases before becoming imaginary at the crossover point.
Intermolecular Interactions through Energy Decomposition: A Chemists’ Perspective*
Mahesh Kumar R., Vijay D., Narahari Sastry G., Subramanian V.
Book chapter, Concepts and Methods in Modern Theoretical Chemistry: Electronic Structure and Reactivity, 2016, DOI Link
View abstract ⏷
Chemists have always strived to comprehend how atoms combine to form compounds of both simple and complex architecture. The variety of compounds which surround us is formed by the difference in the chemical bonding between the mere 118 atoms of the periodic table. There is no denial that these strong chemical bonds that hold the atoms of a molecule together are important, 1-7 but equally important is to understand how these molecules are held together to form large clusters and supramolecular assemblies.8-15 Unraveling the structure of these assemblies and correlating with their functions have been the central theme of many chemical and biological investigations.16-22 In such a scenario, it becomes crucial not only to know the geometrical disposition of the system but also to have a clear idea about the various forces that hold together these assemblies and govern its stability. The forces holding molecules together in such large assemblies play an important role in determining the properties of organic, inorganic, organometallic, biomolecular, and supramolecular systems.23-27 In addition, the role of intermolecular interactions in specicity and selectivity of chemical reactions and biocatalysis, molecular recognition phenomenon, and drug-receptor interactions has also been identied.28-38Although these intermolecular forces are signicantly weaker than the chemical bond, a thorough understanding and quantication of these forces are of utmost importance. Such vital information will not only help to modify the structure and hence the function of drugs and materials but also aid in the design of new functional molecules, nanomaterials, and molecular devices with improved efcacy.39-43 Thus, the study of intermolecular interactions has received intensive attention of researchers and has been the main topic of research in the past 100 years.
Controllable molecular aggregation and fluorescence properties of 1,3,4-oxadiazole derivatives
Wang H., Chen F., Jia X., Liu H., Ran X., Ravva M.K., Bai F.-Q., Qu S., Li M., Zhang H.-X., Bredas J.-L.
Article, Journal of Materials Chemistry C, 2015, DOI Link
View abstract ⏷
The molecular self-assembly behaviour of 2,2′-bis-(4-hexyloxyphenyl)-bi-1,3,4-oxadiazole (BOXD-6) in solution, on surfaces and in bulk crystals, and its photo-physical properties were studied via a combination of experimental techniques and theoretical calculations. It is found that BOXD-6 molecules self-assemble into both H- and J-aggregates at moderate concentration (∼10-4 M) and then transit to exclusive J-aggregates at higher concentration (∼10-3 M) in tetrahydrofuran. In H-aggregation (α polymorph), BOXD-6 adopts a linear conformation and forms a one-dimensional layered structure; in J-aggregation (β polymorph), it adopts a Z-shaped conformation and forms a more ordered two-dimensional layered structure. A π-stacking structure is observed in both cases, and adjacent molecules in J-aggregation show larger displacement along the molecular long axis direction than that in H-aggregation. Although J-aggregates are almost the only component in concentrated solutions (10-3 M), both H- and J-aggregates can be obtained if concentrated solution is transformed onto substrates through a simple drop-casting method. Such a phase transition during film formation can be easily avoided by adding water as a precipitator; a film with pure J-aggregates is then obtained. In order to get more information on molecular self-assembly, intermolecular interaction potential energy surfaces (PES) were evaluated via theoretical calculations at the DFT level (M062x/6-31G∗∗). The PES not only confirm the molecular stacking structures found in crystals but also predict some other likely structures, which will be the target of future experiments.
Effects of functionalization of carbon nanotubes on their dispersion in an ethylene glycol-water binary mixture – a molecular dynamics and ONIOM investigation
Balamurugan K., Baskar P., Kumar R.M., Das S., Subramanian V.
Article, Physical Chemistry Chemical Physics, 2014, DOI Link
View abstract ⏷
The present work utilizes classical molecular dynamics simulations to investigate the covalent functionalization of carbon nanotubes (CNTs) and their interaction with ethylene glycol (EG) and water molecules. The MD simulation reveals the dispersion of functionalized carbon nanotubes and the prevention of aggregation in aqueous medium. Further, residue-wise radial distribution function (RRDF) and atomic radial distribution function (ARDF) calculations illustrate the extent of interaction of -OH and -COOH functionalized CNTs with water molecules and the non-functionalized CNT surface with EG. As the presence of the number of functionalized nanotubes increases, enhancement in the propensity for the interaction with water molecules can be observed. However, the same trend decreases for the interaction of EG molecules. In addition, the ONIOM (M06-2X/6-31+G**:AM1) calculations have also been carried out on model systems to quantitatively determine the interaction energy (IE). It is found from these calculations that the relative enhancement in the interaction of water molecules with functionalized CNTs is highly favorable when compared to the interaction of EG. © the Partner Organisations 2014.
Theoretical study on molecular packing and electronic structure of bi-1,3,4-oxadiazole derivatives
Wang H., Bai F.-Q., Jia X., Cao D., Mahesh Kumar R., Bredas J.-L., Qu S., Bai B., Zhang H.-X., Li M.
Article, RSC Advances, 2014, DOI Link
View abstract ⏷
The molecular aggregation structure of 5,5′-bis(naphthalen-2-yl)-2,2′-bi(1,3,4-oxadiazole) (BOXD-NP) was studied by computing the intermolecular interaction potential energy surface (PES) at density functional theory level based on a dimer model. All B3LYP, CAM-B3LYP and M062x functionals can yield a reliable isolated molecular geometry. The conformation of BOXD-NP obtained with all methods is perfectly planar, indicating good conjugation ability between oxadiazole and naphthalene rings. The vibrational frequencies of BOXD-NP were also calculated using the B3LYP/6-311+G∗∗ method, which showed great consistency with the experimental observations and makes the assignments of the IR spectra more solid. It was revealed that the lowest excited state of BOXD-NP should be assigned as a highly allowed π-π∗ state by TD-DFT calculation. Considering the non-covalent interactions in molecular aggregates, the M062x functional was applied in the construction of the PES. Besides the packing structure found in the crystals, PES also predicted several stable structures, indicating that PES has great ability in guiding molecular self-assembly. Symmetry Adapted Perturbation Theory (SAPT) analysis on these energy-minimum molecular stacking structures revealed that London dispersion forces are the strongest attractive component in the binding. This journal is
Supramolecular functionalization and concomitant enhancement in properties of Au25 clusters
Mathew A., Natarajan G., Lehtovaara L., Hakkinen H., Kumar R.M., Subramanian V., Jaleel A., Pradeep T.
Article, ACS Nano, 2014, DOI Link
View abstract ⏷
We present a versatile approach for tuning the surface functionality of an atomically precise 25 atom gold cluster using specific host-guest interactions between β-cyclodextrin (CD) and the ligand anchored on the cluster. The supramolecular interaction between the Au25 cluster protected by 4-(t-butyl)benzyl mercaptan, labeled Au25SBB18, and CD yielding Au25SBB18â̂©CDn (n = 1, 2, 3, and 4) has been probed experimentally using various spectroscopic techniques and was further analyzed by density functional theory calculations and molecular modeling. The viability of our method in modifying the properties of differently functionalized Au25 clusters is demonstrated. Besides modifying their optoelectronic properties, the CD moieties present on the cluster surface provide enhanced stability and optical responses which are crucial in view of the potential applications of these systems. Here, the CD molecules act as an umbrella which protects the fragile cluster core from the direct interaction with many destabilizing agents such as metal ions, ligands, and so on. Apart from the inherent biocompatibility of the CD-protected Au clusters, additional capabilities acquired by the supramolecular functionalization make such modified clusters preferred materials for applications, including those in biology. © 2013 American Chemical Society.
Structure and stability of (NG)nCN3Be 3+clusters and comparison with (NG)BeY0/+
Pan S., Jalife S., Kumar R.M., Subramanian V., Merino G., Chattaraj P.K.
Article, ChemPhysChem, 2013, DOI Link
View abstract ⏷
The noble gas binding ability of CN3Be3+ clusters was assessed both by ab intio and density functional studies. The global minimum structure of the CN3Be3+ cluster binds with four noble-gas (NG) atoms, in which the Be atoms are acting as active centers. The electron transfer from the noble gas to the Be atom plays a key role in binding. The dissociation energy of the Be-NG bond gradually increases from He to Rn, maintaining the periodic trend. The HOMO-LUMO gap, an indicator for stability, gives additional insight into these NG-bound clusters. The temperature at which the NG-binding process is thermodynamically feasible was identified. In addition, we investigated the stability of two new neutral NG compounds, (NG)BeSe and (NG)BeTe, and found them to be suitable candidates to be detected experimentally such as (NG)BeO and (NG)BeS. The dissociation energies of the Be-NG bond in monocationic analogues of (NG)BeY (Y=O, S, Se, Te) were found to be larger than in the corresponding neutral counter-parts. Finally, the higher the positive charge on the Be atoms, the higher the dissociation energy for the Be-NG bond becomes. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Interaction of ethylene glycol-water clusters with aromatic surfaces
Kumar R.M., Baskar P., Balamurugan K., Das S., Subramanian V.
Article, RSC Advances, 2013, DOI Link
View abstract ⏷
The gas phase geometries of ethylene glycol-water (EGmW n) (where m = 0-4, n = 0-4; m + n ≤ 4) clusters adsorbed on a fragment of carbon nanotube have been investigated using density functional theory based M05-2X and ωB97XD methods employing various basis sets. With a view to assess the effect of curvature on the hydrogen bonding pattern between ethylene glycol and water molecules, calculations on intermolecular complexes comprising a planar aromatic surface and EGmWn clusters have been carried out. Results obtained from the electronic structure calculations and Bader's electron density analysis reveal that C-H⋯π, O-H⋯π and lone pair⋯π interactions are predominant in the stabilization of EGmWn and the corresponding complexes with fragments of a carbon nanotube and graphene. Further, the role of the π-cloud on the stability of EGmWn is illustrated by comparing the interaction energies of clusters in the presence and absence of an aromatic surface. © 2013 The Royal Society of Chemistry.
Improving the hydrogen storage capacity of metal organic framework by chemical functionalization
Kumar R.M., Sundar J.V., Subramanian V.
Article, International Journal of Hydrogen Energy, 2012, DOI Link
View abstract ⏷
The hydrogen storage capacity of transition metal decorated terphenyl linkers was investigated using density functional theory based M05-2X, M06 and wB97XD methods. The -OH and -SH groups are used as anchors to bind various transition metals such as Sc, Ti, V, and Cr on terphenyl linker. It has been found that each transition metal can bind four hydrogen molecules through Kubas interaction. The correlation between electron density at the bond critical point corresponding to H-H bond and concomitant intermolecular distances between transition metal and hydrogen molecules has been used to illustrate the Kubas mechanism. Further, to estimate the bulk storage capacity, 42 hydrogen molecules are allowed to interact with the new metal organic framework fragment in all possible binding sites. The calculated interaction energy per hydrogen molecule is found to be -3.38 kcal/mol. Comparison of this value with previous reports shows that this energy is suitable for room temperature hydrogen storage applications. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Studies on the encapsulation of F – in single walled nanotubes of different chiralities using density functional theory calculations and car-parrinello molecular dynamics simulations
Ravinder P., Kumar R.M., Subramanian V.
Article, Journal of Physical Chemistry A, 2012, DOI Link
View abstract ⏷
In this study, the encapsulation of F - in different nanotubes (NTs) has been investigated using electronic structure calculations and Car-Parrinello molecular dynamics simulations. The carbon atoms in the single walled carbon nanotube (CNT) are systematically doped with B and N atoms. The effect of the encapsulation of F - in the boron nitride nanotube (BNNT) has also been investigated. Electronic structure calculations show that the (7,0) chirality nanotube forms a more stable endohedral complex (with F -) than the other nanotubes. Evidence obtained from the band structure of CNT calculations reveals that the band gap of the CNT is marginally affected by the encapsulation. However, the same encapsulation significantly changes the band gap of the BNNT. The density of states (DOS) derived from the calculations shows significant changes near the Fermi level. The snapshots obtained from the CPMD simulation highlight the fluctuation of the anion inside the tube and there is more fluctuation in BNNT than in CNT. © 2012 American Chemical Society.
Density functional studies on the hydrogen storage capacity of boranes and alanes based cages
Gopalsamy K., Prakash M., Mahesh Kumar R., Subramanian V.
Article, International Journal of Hydrogen Energy, 2012, DOI Link
View abstract ⏷
The hydrogen storage (H-storage) capacity of various boranes and alanes have been investigated using density functional theory (DFT) based M05-2X method employing 6-31+G** basis set. The changes in the H-storage capacities of borane and alane upon substitution of antipodal atoms in the cages by C, Si, and N have also been investigated. It is found from the calculations that a maximum of 20 H 2 molecules can be adsorbed on the deltahedron faces of these cages. The maximum gravimetric density has been observed for boranes when compared to alanes. The H-storage capacity of closo-borane dianion [B 12H 12] 2-, monocarborane [CB 11H 12] 1-, dicarborane [C 2B 10H 12], and closo-azaborane [NB 11H 12] cages is almost similar (∼22 wt.%). Among these cages, B BB dianion show higher binding energy (BE) and BE per H 2 molecule (BE/nH 2) which are 181.06 and 9.03 kJ/mol, respectively. In the case of alanes, dicarbalane [C 2Al 10H 12] has maximum H-storage capacity of 11.6 wt.%. Based on these findings, a new MOF with carborane (MOF-5 CC) as linker has been designed. The calculation on the new MOF-5B CC reveals that it has H-storage capacity of 6.4 wt.% with BE/nH 2 of 3.02 kJ/mol. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
On the perturbation of the H-Bonding Interaction in ethylene glycol clusters upon hydration
Kumar R.M., Baskar P., Balamurugan K., Das S., Subramanian V.
Article, Journal of Physical Chemistry A, 2012, DOI Link
View abstract ⏷
Ab initio and density functional methods have been employed to study the structure, stability, and spectral properties of various ethylene glycol (EG m) and ethylene glycol-water (EG mW n) (m = 1-3, n = 1-4) clusters. The effective fragment potential (EFP) approach was used to explore various possible EG mW n clusters. Calculated interaction energies of EG mW n clusters confirm that the hydrogen-bonding interaction between EG molecules is perturbed by the presence of water molecules and vice versa. Further, energy decomposition analysis shows that both electrostatic and polarization interactions predominantly contribute to the stability of these clusters. It was found from the same analysis that ethylene glycol-water interaction is predominant over the ethylene glycol-ethylene glycol and water-water interactions. Overall, the results clearly illustrate that the presence of water disrupts the ethylene glycol-ethylene glycol hydrogen bonds. © 2012 American Chemical Society.
Interaction of carbon nanotube with ethylene glycol-water binary mixture: A molecular dynamics and density functional theory investigation
Balamurugan K., Baskar P., Mahesh Kumar R., Das S., Subramanian V.
Article, Journal of Physical Chemistry C, 2012, DOI Link
View abstract ⏷
Classical molecular dynamics (MD) simulation has been carried out on model systems composed of ethylene glycol (EG) and carbon nanotube (CNT) in water (WAT) medium to gain insight into the interaction between them. The analysis of the MD results reveals that the EG molecules aggregate around CNT expelling water molecules due to the hydrophobic-hydrophobic interaction. Hydrogen-bonding (H-bonding) interaction between two EG molecules increases in the presence of CNT. Further, the presence of CNT decreases the solubility of EG in water. The analysis of the dihedral angle of EG reveals that the CNT induces conformational changes in EG. Specifically, a small fraction of the gauche form of EG is converted into trans. In addition, electronic structure calculations have also been carried out on model systems to quantitatively determine the binding energy (BE). The M05-2X/6-31+G** level calculations on the model systems show that the BE of CNT-WAT and CNT-EG ranges from 11.76 to 17.78 kJ/mol. It is interesting to note from the electronic structure calculations that the BE of trans EG with CNT is more than that of gauche EG with CNT in accordance with the findings from the MD simulation. © 2012 American Chemical Society.
The role of C-H…π interaction in the stabilization of benzene and adamantane clusters
Kumar R.M., Elango M., Parthasarathi R., Vijay D., Subramanian V.
Article, Journal of Chemical Sciences, 2012, DOI Link
View abstract ⏷
In this investigation, a systematic attempt has been made to understand the interaction between adamantane and benzene using both ab initio and density functional theory methods. C-H...π type of interaction between C-H groups of adamantane and π cloud of benzene is found as the important attraction for complex formation. The study also reveals that the methylene (-CH2) and methine (-CH) groups of adamantane interact with benzene resulting in different geometrical structures. And it is found that the former complex is stronger than the later. The diamondoid structure of adamantane enables it to interact with a maximum of four benzene molecules, each one along the four faces. The stability of the complex increases with increase in the number of benzene molecules. The energy decomposition analysis of adamantane-benzene complexes using DMA approach shows that the origin of the stability primarily arises from the dispersive interaction. The theory of atoms in molecules (AIM) supports the existence of weak interaction between the two systems. The electrostatic topography features provide clues for the mode of interaction of adamantane with benzene. © Indian Academy of Sciences.
Density functional theory studies on ice nanotubes
Kumar R.M., Elango M., Parthasarathi R., Subramanian V.
Article, Journal of Physical Chemistry A, 2011, DOI Link
View abstract ⏷
The structure and stability of quasi one-dimensional (1D) ice nanotubes (INTs) have been investigated using Density Functional Theory (DFT) based Becke's three parameter Lee-Yang-Parr exchange and correlation functional (B3LYP) method employing various basis sets. Four different INTs, namely, (4,0)-INT, (5,0)-INT, (6,0)-INT, and (8,0)-INT with different lengths have been considered in this study. The calculated stabilization energies (SEs) illustrate that the stability of INT is proportional to its length and diameter. Further, the encapsulation of various gas molecules (CO 2, N 2O, CO, N 2, and H 2) inside the INTs has also been investigated. The calculated SEs of different endohedral complexes reveal that all these gas molecules are stable inside the tubes. The Bader's theory of atoms in molecule (AIM) has been used to characterize intra-and inter-ring H-bonding interactions. The electron density topological parameters derived from AIM theory brings out the difference between the intra-and inter-ring H-bonds of INTs. © 2011 American Chemical Society.
Interaction of H2 with fragments of MOF-5 and its implications for the design and development of new MOFs: A computational study
Article, International Journal of Hydrogen Energy, 2011, DOI Link
View abstract ⏷
The interaction energies (IEs) of H2 and various organic ligands have been computed using coupled-cluster method with singles, doubles, and noniterative triples (CCSD(T)) at the complete basis set (CBS) limit. The density fitting-density functional theory-symmetry adapted perturbation theory (DF-DFT-SAPT) approach has been used to probe the nature of interaction between H2 and organic linkers. It has been found that dispersive interaction predominantly stabilizes the intermolecular complex formation of H2 on a variety of organic linkers. Furthermore, H2 binding affinity of inorganic connectors is improved by partial isomorphic substitution of Zn by different metal ions such as Fe, Co, Ni and Cu. A new modified metal-organic framework (MOF-5 M) has been designed based upon the insight from the organic and inorganic fragments. The present study provides valuable information required for the design of novel MOFs with improved affinity for H2 adsorption. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Quantum mechanical studies on interaction of carbohydrate with nanomaterials
Article, Journal of Biomedical Nanotechnology, 2011, DOI Link
View abstract ⏷
The interactions between the fragment of various nanotubes (NTs) and carbohydrate (β-D-glucose) has been investigated using quantum mechanical methods using different basis sets in gas phase. The most stable isomer of each complex favors multiple CH• • •π contacts which arise due to the orientation of the hydrophobic surface of the carbohydrate with reference to the curved or planar aromatic systems. The carbohydrate recognition surface of the aromatic system referred as "three point landing surface" are important in the stabilization of carbohydrate-π complexes. Copyright © 2011 American Scientific Publishers All rights reserved.
Studies on the structure and stability of cyclic peptide based nanotubes using oligomeric approach: A computational chemistry investigation
Vijayaraj R., Sundar Raman S., Mahesh Kumar R., Subramanian V.
Article, Journal of Physical Chemistry B, 2010, DOI Link
View abstract ⏷
In this study, an attempt has been made to investigate the structure, dynamics, and stability of cyclic peptide nanotubes (CPNTs) formed by the self-assembly of cyclic peptides (CPs) using classical molecular dynamics (MD) simulation and semiempirical quantum chemistry calculation employing PM6 Hamiltonian with the dispersion correction and hydrogen-bonding interaction (DH2). The structure and energetics of monomer and various oligomeric CPNTs have been investigated by considering the (cyclo-[(d-Ala-l-Ala)4]) peptide as the model for CP. Although the formation of CPNTs has been intensively studied, the present study adds valuable information to the de novo design of CPNTs. Various geometrical parameters extracted from the MD simulation reveal that the terminal residues are loosely hydrogen bonded to the inner subunits regardless of degree of oligomerization. The hydrogen bonds present in the inner core regions are stronger than the terminal residues. As the degree of oligomerization increases, the stability of the tube increases due to the hydrogen-bonding and stacking interactions between the subunits. The results show that the binding free energy increases with the extent of oligomerization and reaches saturation beyond pentamer CPNT. In addition, hydrophobic and electrostatic interactions play crucial roles in the formation of CPNTs. Analysis of both structure and energetics of the formation of CPNTs unveils that the self-assembly of dimer, trimer, and tetramer CPNTs are the essential steps in the growth of CPNTs. © 2010 American Chemical Society.
Expedient synthesis of coumarin-coupled triazoles via ‘click chemistry’ leading to the formation of coumarin-triazole-sugar hybrids
Kumar K.K., Kumar R.M., Subramanian V., Das T.M.
Article, Carbohydrate Research, 2010, DOI Link
View abstract ⏷
Coumarin-based triazoles were synthesized from 3-azidomethylcoumarin and a terminal acetylenic compound. Uncatalysed thermal conditions result in a mixture of both 1,4- and 1,5-regioisomers or the thermodynamically more stable 1,4-regioisomer, whereas the Cu(I)-catalysed reaction affords only the favourable 1,4-regioisomer. B3LYP/6-31G(d) level of theory has been used to calculate geometry and frequency features of the reactants, transition states (TSs) and products. Computational studies further reveal that 1,4-regioisomeric products are more favourable and also thermodynamically more stable compared to the 1,5-regioisomers. © 2010 Elsevier Ltd. All rights reserved.
Carbohydrate-aromatic interactions: The role of curvature on XH⋯π interactions
Article, Journal of Physical Chemistry A, 2010, DOI Link
View abstract ⏷
The interaction between the fragment of carbon nanotube (CNT) and carbohydrates has been investigated using MP2 and M05-2X methods using various basis sets in gas phase. Three carbohydrates, viz., β-Dglucose, β-D-galactose, and β-D-xylose with different degree of hydrophobic nature have been selected for this investigation. With a view to assess the effect of curvature on the interaction between the carbohydrates and CNT, calculations on intermolecular complexes comprising of coronene (COR) and carbohydrates have also been carried out in gas phase. Results obtained from electronic structure calculations combined with the Bader's electron density analysis reveal that CH⋯π interaction is the predominant one in the stabilization of the carbohydrate-CNT and carbohydrate-COR complexes. Furthermore, the importance of OH⋯π and lone pair⋯π (lp⋯π) interactions are also evident from the results. The calculated BEs for the various carbohydrate-CNT and carbohydrate-COR complexes at M05-2X with dual basis set [aug-cc-pVTZ for carbohydrate + cc-pVTZ for both CNT and COR] vary from -2.52 to -5.14 and from -4.14 to -8.04 kcal/mol, respectively. The corresponding BEs obtained from MP2/6-311++G(d,p)//M05-2X/6-31+G(d,p) level of calculation range from -4.92 to -9.93 and from -6.75 to -12.53 kcal/mol. Close scrutiny of the energetics of all the complexes elucidate that the electron correlation energy (dispersion energy) significantly contribute to the stability of these complexes. It is found from the analysis of geometrical parameters and BEs that the interplay of orientation of the X-H (X = C and O) bond to the π-surface is crucial for the recognition and further stabilization. Molecular electrostatic potential (MESP) isosurfaces of curved and planar surfaces have clearly provided the difference between the π-electron distributions. Evidences form the energy decomposition analysis elicit that the dispersive interaction plays a significant role in the overall stabilization of the complexes. And, it is possible to observe the delicate balance between the electrostatic interaction and the exchange-repulsion energy. © 2010 American Chemical Society.
Ab Initio and DFT studies on methanol-water clusters
Mandal A., Prakash M., Kumar R.M., Parthasarathi R., Subramanian V.
Article, Journal of Physical Chemistry A, 2010, DOI Link
View abstract ⏷
The gas-phase geometries, binding energies (BEs), vibrational spectra, and electron density topological features of methanol (M), water (W), and methanol-water mixed clusters (MmWn, where m = 0-4 and n = 0-4; m + n ≤; 4) have been calculated using Hartree-Fock, second-order Møller-Plesset perturbation, and density functional theory with Becke three-parameter hybrid functional, combined with Lee-Yang-Parr correlation functional methods. Bader's "atoms in molecules" theory has been used to analyze the hydrogen bonding network. To understand the effect of cooperativity, we have performed natural bond orbital, analysis and reduced variational space decomposition analysis. The results show that BEs of methanol and mixed clusters are higher than those of water clusters due to the electron-donating nature of the methyl group. These findings are in accordance with the role of cooperative polarization and cooperative charge transfer in the methanol and mixed clusters. As the size of the cluster increases, the contribution from the cooperative effects also increases. The cooperativity contributes ∼14 and 24% of stabilization in trimers and tetramers, respectively. The calculated voH frequencies at MP2/6-311++G(d,p) are in close agreement with the corresponding experimental values. © 2010 American Chemical Society.
