A Charge Transfer State Induced By Strong Exciton Coupling In A Cofacial Mu-Oxo-Bridged Porphyrin Heterodimer

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, mu-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 similar to 130 ps. The high-energy triplet CT state ((CT)-C-3 = 1.68 eV) lasts for nearly 105 mu s prior to relaxing to the ground state.