A computational study on the effect of structural isomerism on the excited state lifetime and redox energetics of archetype iridium photoredox catalyst platforms [Ir(ppy)₂(bpy)]⁺ and Ir(ppy)₃.

This article investigates the influence of structural isomerism on the excited state lifetime and redox energetics of cyclometalated iridium(III) photoredox catalysts, specifically heteroleptic [Ir(ppy)₂(bpy)]⁺ and homoleptic Ir(ppy)₃ complexes. Using density functional theory and spin–orbit coupling analyses, the study finds that while redox potentials vary minimally among isomers, radiative and non-radiative decay rates of the triplet metal-to-ligand charge transfer (³MLCT) excited states differ significantly due to changes in transition dipole moments, vertical energy gaps, spin–orbit coupling efficiency, and vibrational reorganization energies linked to metal–ligand bond dynamics. The authors introduce a conceptual framework based on the vectorial difference of permanent dipole moments between ground and excited states to rationalize variations in radiative lifetimes, highlighting the role of ligand orientation and metal d orbital involvement. These insights emphasize how subtle structural modifications can be strategically employed to optimize the photophysical properties and catalytic performance of iridium-based photoredox catalysts.