Photochemical charge separation in supramolecular phthalocyanine-multifullerene conjugates assembled by crown ether-alkyl ammonium cation interactions

Abstract

Self-assembled phthalocyanine-multifullerene donor-acceptor conjugates have been formed by crown ether-ammonium cation dipole-ion binding strategy to probe the photochemical charge separation. To achieve this, phthalocyanine is functionalized to possess four 18-crown-6 moieties on the macrocycle periphery, whereas fullerene is functionalized to possess an alkyl ammonium cation of short and long chain lengths. Stable donor-acceptor conjugates accommodating multifullerene entities have been obtained by the crown ether-ammonium cation inclusion complexation. From the efficient fluorescence quenching of the zinc phthalocyanine by the bound fullerene entities, the rate constants of charge separation are evaluated to be slightly larger for closely held via shorter alkyl chain length fullerene, which are also larger compared to the earlier reported analogous zinc porphyrin-multifullerene conjugate. Nanosecond transient absorption studies yielded spectral signatures corresponding to both the phthalocyanine radical cation and fullerene radical anion at the same time, providing evidence of light-induced electron transfer within the conjugates. The evaluated lifetimes of the radical ion pairs in the present phthalocyanine-fullerene conjugates are found to be hundreds of nanoseconds and are much longer compared to the earlier reported conjugate of zinc porphyrin analogue, revealing higher possible usage of the generated radical ion pairs.