Characterization of photo-induced electron and hole transfer in a porphyrin based ambipolar organic molecule with cascade energy levels

A porphyrin based ambipolar organic molecule consisting of styrene based triphenylamine derivative (MTPA) as electron donor, s-triazine group (TRC) as electron acceptor 1 and metal-free tetraphenyl porphyrin (HTPP) as electron acceptor 2 was synthesized and characterized using computational methods and electrochemical and spectroscopic measurements. The kinetics analysis indicates that the photo-induced charge-separated states, MTPA.+-TRC-HTPP.-, were generated by sequential electron transfers from MTPA to TRC then to HTPP and/or a direct hole transfer from HTPP to MTPA. In toluene, the charge-separated states were formed with 54% through electron transfer and 46% through hole transfer once MTPA moiety was excited. However, in dichloromethane, they were formed with 75% through electron transfer and 25% through hole transfer. Furthermore, more charge-separated species were generated in dichloromethane than in toluene.