Ligand-to-metal charge transfer driven by excited-state antiaromaticity in metallohexaphyrins

Abstract

We investigated the effect of excited-state antiaromaticity on the ligand-to-metal charge transfer (LMCT) process of metallohexaphyrins. According to Baird rule, the aromatic metallohexaphyrins in the S-0 state become antiaromatic in the S-1 state. Because of the metal-ligand redox-like nature of LMCT process, the LMCT process can release the antiaromatic nature and its energetic destabilization. The metallohexaphyrins show a correlation between the S-0-state aromaticity and time constants for the LMCT process, which well demonstrates that the excited-state antiaromaticity at the Franck-Condon state acts as a driving force for the LMCT process. These findings elucidate the effect of excited-state antiaromaticity on the excited-state behaviors and further provide an insight into the photochemistry of organic molecules.