Absorption spectrophotometric, NMR and theoretical investigations on ground state non-covalent interaction of C60 and C70 with a designed trihomocalix[6]arene in solution

Abstract

The present paper reports the spectroscopic investigations on non-covalent interaction of fullerenes C60 and C70 with a designed trihomocalix[6]arene (2) in toluene. UV–vis studies reveal appreciable ground state interaction between fullerenes and 2. Jobs method of continuous variation establishes 1:1 stoichiometry for fullerene–2 complexes. Binding constant (K) data reveals that 2 binds C70 more strongly compared to C60, i.e. KC60–2=47,540dm3mol−1 and KC70–2=86,360dm3mol−1. Proton NMR studies provide very good support in favor of strong binding between C70 and 2. Estimation of solvent reorganization energy (RS) evokes that C70–2 complex is stabilized more compared to C60–2 complex as RS(C60–2)=−1.162eV and RS(C70–2)=−1.244eV. Semiempirical calculations at third parametric level of theory in vacuo evoke the single projection structures of the fullerene–2 complexes and interpret the stability difference between C60 and C70 complexes of 2 in terms of enthalpies of formation values.