Zinc porphyrazine: An efficient receptor for N-methylfulleropyrrolidine

This article reports the non-covalent interaction of N-methylfulleropyrrolidine (A) with a designed zinc porphyrazine (ZnPz) in toluene. An absorption band due to charge transfer (CT) transition is observed in the visible region of the absorption spectrum. The experimentally determined CT transition energies (h[Formula: see text] for the complexes of A with ZnPz and some other electron acceptors, namely, [Formula: see text]-chloranil, [Formula: see text]-chloranil, DDQ, TCNE, and TCNQ, are well correlated (through Mulliken’s equation) with the electron affinities of the acceptors. From an analysis of this correlation, the electron affinity value of A ((3.580 ± 0.500) eV) is determined in solution for the first time. The binding constant ([Formula: see text] of the A-ZnPz system is estimated from both UV-vis ([Formula: see text] (43730 ± 2185) dm[Formula: see text] mol[Formula: see text]. Steady-state fluorescence measurements ([Formula: see text] (183790 ± 3400) dm[Formula: see text] mol[Formula: see text] and the average value of [Formula: see text] for the A-ZnPz system is calculated to be 113760 ± 2790 dm[Formula: see text] mol[Formula: see text], indicating that strong non-covalent interaction occurs between A and ZnPz in solution. Similar to the steady-state fluorescence experiment, efficient quenching of the fluorescence of ZnPz in the presence of A receives strong support from the fluorescence microscope image of ZnPz recorded before and after complexation with A. Time-resolved experiments determine the rate constant for charge separation of the excited singlet (1.174 × 10 7 sec[Formula: see text] and the quantum yield of charge separation of the excited singlet of the A-ZnPz system (0.031), which categorically rules out the possibility of any diffusion-driven process for the investigated supramolecule. Quantum chemical calculations at the Hybrid-DFT level of theory in the gas phase provide strong support for the high [Formula: see text]value of the A-ZnPz system.