Carboxamidoquinoline appended calix[4]arene-1,3-di-conjugate (L) has been synthesized and characterized and its single crystal XRD structure has been established. L has been shown to act as selective ratiometric turn-on fluorescence sensor for Zn 2+ up to a lowest concentration of 183 ± 18 ppb (2.82 μM) with a nine-fold enhancement by exhibiting blue-green emission. The coordination features of the species of recognition have been computationally evaluated by DFT methods and found to have distorted tetrahedral Zn 2+ center in an N 4 core. The spherical nano-structural features observed for L in TEM are being transformed into the Koosh nano-flower like structure when complexed with Zn 2+ and hence these two can be easily differentiated. Even the features observed in AFM can distinctly differentiate L from its Zn 2+ complex. © 2012 The Royal Society of Chemistry.