Electropolymerizable meso-Tetrakis Biphenyl-Bis(bithiophene) Zinc Porphyrin: Ground and Excited State Properties in Solution and in Films with Axially Coordinated C₆₀

Abstract

An electropolymerizable zinc porphyrin carrying eight entities of peripheral bithiophene, 4 was newly designed and synthesized. In this design, the bithiophene entities were separated by a biphenyl spacer to minimize ground state interactions perturbing porphyrin π-electronic structure. By multi-cyclic voltammetry, thin-films of 4 were formed on transparent FTO electrode and were characterized by optical, electrochemical and STM measurements. Further, the ability of zinc porphyrin in 4 to axially coordinate phenyl imidazole functionalized fullerene, C60Im both in solution and on the film interface was performed and characterized. Fluorescence quenching of zinc porphyrin both in solution and in the film was observed upon binding of C60Im. Femtosecond transient absorption studies revealed excited state charge separation for the dyad in solution wherein the measured rate of charge separation, k CS and charge recombination, k CR were found to be 2 × 1010 s−1 and 1.2 × 109 s−1, respectively. In contrast, transient absorption studies performed on the dyad in the film were suggestive of energy transfer with minimal contributions from electron transfer. The present study brings out the importance of modulating photochemical reactivity of donor-acceptor dyad in film as compared to that in solution.