Picosecond MLCT Deactivation in Co(ppy)3 via Jahn‐Teller Distortion

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‐to‐ligand charge transfer (MLCT) character, unlike other Co complexes that generally have ligand‐to‐metal charge transfer or ligand‐field transitions in this energy range. Ground‐state recovery occurs in 8.65 ps in dichloromethane. Density functional theory (DFT) calculations show that the MLCT state undergoes Jahn‐Teller distortion and converts to a 5‐ coordinate 3MC state in which one Co‐N bond is broken. The results highlights a potential pitfall of heteroleptic‐bidentate ligands when designing strong‐field ligands for transition metal chromophores.