Photophysical insights on a new supramolecular recognition element comprising PyC60 and a bisporphyrin studied in solution

Abstract

The present work reports detailed photophysical insights on supramolecular interaction between C60 pyrrolidine tris-acid ethyl ester (PyC60) and a designed diporphyrin (1) in toluene. Both UV–vis and steady state fluorescence studies indicate effective complexation between PyC60 and 1 as revealed from the value of binding constant (K) of PyC60–1 complex, i.e., KPyC60–1 (UV–vis) = 7625 dm3·mol−1 and KPyC60–1 (fluorescence) = 9550 dm3·mol−1. Time-resolved fluorescence measurements evoke that the decay of photoexcited 1 in presence of PyC60 occurs only via static quenching mechanism and the magnitude of bimolecular quenching constant value for such system is enumerated to be 9.033 × 1011 dm3·mol−1·sec−1. In 1,2-dichlorobenzene (DCB), PyC60–1 system exhibits appreciable value of rate-constant of charge-separation (kcs) and quantum yield of charge-separation (ϕCS) than that observed in toluene. However, magnitude and order of both kcs (=5.35 × 107) and ϕCS (= 0.085) value for the PyC60–1 system estimated in DCB indicate that like toluene, there is no possibility of electron transfer in DCB. Both 1H and 13C NMR spectra of PyC60 molecule show appreciable shift of functional protons and carbon moiety of parent molecule in presence of 1, respectively. Quantum chemical calculations by ab initio method in vacuo establish the geometric structure of PyC60–1 complex and predict that dispersive forces associated with π-π interaction play significant role behind non-covalent interaction between PyC60 and 1.