Spectroscopic and quantum chemical investigation on non-covalent interaction in chromophore appended fullerene complexes of calix[4]arene

Abstract

The present paper describes the spectroscopic and theoretical insights on non-covalent interaction of a calix[4]arene molecule, namely, 4-iso-propyl-calix[4]arene (1) with chromophore appended fullerenes, namely, tert-butyl-(1,2-methanofullerene)-61-carboxylate (2) and [6,6]-phenyl-C71- butyric acid methyl ester (3) in solvents having varying polarity, viz., toluene and benzonitrile. Absorption spectrophotometric studies reveal appreciable ground state interaction between fullerenes and 1. The most fascinating feature of the present study is that 1 binds very effectively with both 2 and 3 as obtained from binding constant (K) data of such complexes; i.e., K2–1 and K3–1 exhibit value of 4.53×105dm3mol−1 (7.95×105dm3mol−1) and 13.35×105dm3mol−1 (27.62×105dm3mol−1) in toluene (benzonitrile), respectively. The effect of solvent over the complexation between fullerenes and 1 is clearly observed from the trend in the K values. Estimation of solvent reorganization energy (RS) evokes that both 2–1 and 3–1 complexes are stabilized more in toluene compared to benzonitrile. Molecular mechanics force field (MMMF) calculations in vacuo evoke geometrical structures of the 2–1 and 3–1 complexes and reveal interesting feature regarding binding pattern of fullerenes toward 1 in terms of heat of formation value of the respective complexes.