Experimental and computational anion binding studies of meso-substituted one-walled phthalimide-based Calix[4]pyrrole

Abstract

Anion binding studies of meso‑substituted one-walled phthalimide-based calix[4]pyrrole (m-PC4P, 6) were investigated through UV–vis spectroscopy in acetonitrile and corroborated by time-dependent density functional theory (TD-DFT) calculations using 6–311G(d) basis set. Notably, to our expectation, the m-PC4P (6) displayed higher anion binding affinities in comparison to the parent C4P system, probably due to the additional weak CH-anion interactions besides four NH-hydrogen bonds of the C4P framework (supported by 1H NMR evidence). Herein, we have observed the usual trend with halide anions (used as their tetrabutylammonium salts), i.e. with increase in size of the halides from fluoride to iodide, the anion binding affinity decreases. Moreover, with the nitrate anion, appreciable better binding was observed in the case of m-PC4P (6) as compared to the simple C4P (1).