Probing the influence of connectivity and dual bridging on the structural, electronic, photophysical, supramolecular, and charge transfer properties of macrocycles and nanohoops

Publications

Probing the influence of connectivity and dual bridging on the structural, electronic, photophysical, supramolecular, and charge transfer properties of macrocycles and nanohoops

Year : 2026

Publisher : Royal Society of Chemistry

Source Title : Materials Chemistry Frontiers

Document Type :

Abstract

Radially oriented π-conjugated macrocycles exhibit unique size-dependent photophysical, electrochemical, supramolecular, and charge-transport properties. Establishing structure–property relationships is important for the rational design of functional macrocycles. In this study, we investigated how simultaneous modulation of molecular connectivity and bridging motifs influences the properties of conjugated macrocycles. The all-carbon-bridged nanohoop [12]S6 was synthesized by connecting spiro[fluorene-9,9′-xanthene] (SFX) units through 4–4 linkages. In contrast, the dual-bridged macrocycle [12]S4C2 was obtained by replacing two SFX units with N-bridged carbazole (Cz) units and modifying the connectivity between SFX and Cz units to 4–5 linkages, resulting in a more elliptical macrocyclic geometry. A detailed experimental and theoretical comparison between [12]S6 and [12]S4C2, including electrochemical, photophysical, supramolecular, and charge-transport investigations, was carried out. The introduced structural modifications enhanced the molar absorption coefficient, photoluminescence quantum yield, and brightness of [12]S4C2. Host–guest studies revealed stronger supramolecular association of [12]S4C2 with C60, indicating improved accommodation of the fullerene guest within the modified framework. In contrast, charge-transport analysis showed that the electron and hole mobilities of the nanohoop [12]S6 are approximately two times greater than those of [12]S4C2, while both macrocycles exhibited higher hole mobilities than electron mobilities. Dimer analysis indicated dominant SFX–SFX interactions in [12]S6, whereas Cz–Cz interactions were more prominent in [12]S4C2. These results demonstrate that subtle variations in connectivity and bridging motifs can effectively tune the structural and functional properties of conjugated macrocycles.