A charge transfer state induced by strong exciton coupling in a cofacial μ-oxo-bridged porphyrin heterodimer
Niloofar Zarrabi, Brandon J. Bayard, Sairaman Seetharaman, Noah Holzer, Paul A. Karr, Susanna Ciuti, Antonio Barbon, Marilena Di Valentin, Art van der Est, Francis D’Souza, Prashanth K. Poddutoori
Abstract
Photosensitizers with high energy, long lasting charge-transfer states are important components in systems designed for solar energy conversion by multistep electron transfer. Here, we show that in a push-pull type, μ-oxo-bridged porphyrin heterodimer composed of octaethylporphyrinatoaluminum(iii) and octaethylporphyrinatophosphorus(v), the strong excitonic coupling between the porphyrins and the different electron withdrawing abilities of Al(iii) and P(v) promote the formation of a high energy CT state. Using, an array of optical and magnetic resonance spectroscopic methods along with theoretical calculations, we demonstrate photodynamics of the heterodimer that involves the initial formation of a singlet CT which relaxes to a triplet CT state with a lifetime of ∼130 ps. The high-energy triplet CT state (3CT = 1.68 eV) lasts for nearly 105 μs prior to relaxing to the ground state.