Supramolecular dyad derived from a buckybowl series of O2N2-donor naphthodiaza-crowns coordinated to C60: photophysical, NMR and theoretical studies

Abstract

Supramolecular complexation of C60 with L1-L5 were studied in toluene, chloroform and 1,2-dichlorobenzene solvents using UV–vis, fluorescence, 1H, 13C NMR spectroscopy as well as density functional theory (DFT) calculations. The Job’s plot of continuous variation method established 1:1 stoichiometry for L1-L5/C60. Binding constants (K) calculated for L1-L5/C60 were also determined employing UV–vis and fluorescence spectroscopy. Both steady-state and time-resolved fluorescence spectroscopic surveys showed remarkable fluorescence quenching phenomenon for L1-L5 in the presence of C60 which was primarily attributed to involvement of a static process. The observed fluorescence quenching in L1–L5 was described in terms of both π–π and n–π interactions of the naphthalene moieties and the nitrogen donor groups on the aza-crown macrocyclic ligands with C60, respectively. Moreover, DFT calculations using B3LYP/6-31G* basis set confirmed on the aforesaid π–π interaction of naphthalene groups on the aza-crowns with C60. The DFT calculations also established significant distributions of charge between C60 and L1-L5 in according to the electronic structure and geometry of L1-L5/C60, very similar to phthalocycnine/C60 systems.