Picosecond Metal-to-Ligand Charge-Transfer Deactivation in Co(ppy)₃ via Jahn–Teller Distortion

Abstract

The excited-state dynamics of fac-Co(ppy) 3 , where ppy = 2-[2-(pyridyl)phenyl], are measured with femtosecond UV−vis transient absorption spectroscopy. The initial state is confirmed with spectroelectrochemistry to have significant metal-toligand charge transfer (MLCT) character, unlike other Co complexes that generally have ligand-to-metal charge transfer or ligandfield transitions in this energy range. Ground-state recovery occurs in 8.65 ps in dichloromethane. Density functional theory calculations show that the MLCT state undergoes Jahn−Teller distortion and converts to a five-coordinate triplet metal-centered state in which one Co−N bond is broken. The results highlight a potential pitfall of heteroleptic bidentate ligands when designing strong-field ligands for transition-metal chromophores.