Self-assembled supramolecular triad composed of fulleropyrrolidine bearing two pyridine moieties axially coordinated to two zinc porphyrins

Abstract

Spectroscopic, redox, and photochemical behavior of a self-assembled donor-acceptor triad formed by axial coordination of zinc meso-tetraphenylporphyrin, Zn ( TPP ) with fulleropyrrolidine bearing two pyridine moieties ( C 60( Py )2) was investigated. The UV-visible and 1 H NMR spectral studies revealed supramolecular 1:2 triad formation between C 60( Py )2 and Zn ( TPP ). The determined overall formation constant, K was as large as 1.45 × 104 mol -2 in o-dichlorobenzene (o-DCB). The 1 H NMR studies revealed axial coordination of both the pyridine entities of C 60( Py )2 to the central metal ion of the zinc porphyrins. Electrochemical studies of the isolated self-assembled triad in o-DCB established the molecular stoichiometry of the supramolecular complex possessing one C 60( Py )2 and two Zn ( TPP ) entities. The excited state electron transfer reactions were monitored by both steady-state emission as well as transient absorption techniques. In o-DCB, upon coordination of the pyridine entities of C 60( Py )2 to two Zn ( TPP ), the main quenching pathway involved charge-separation from the singlet excited Zn ( TPP ) to the C 60 moiety. However, in a coordinating solvent like PhCN , intermolecular electron-transfer takes place from the triplet excited state of Zn ( TPP ) to the C 60 moiety.