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

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 S0 state become antiaromatic in the S1 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 S0‐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. Here, the redox‐like LMCT process having the character of electron transfer between metal and ligand acts as a tool for alleviation of antiaromatic destabilization. The correlation between the S0‐state aromaticity and the time constants for the LMCT process well demonstrates that the LMCT process is driven by the excited‐state antiaromaticity and acts as a route for a relief of antiaromatic destabilization.