Spin density distribution after electron transfer from triethylamine to an [Ir(ppy)2(bpy)]+ photosensitizer during photocatalytic water reduction

The photoreduction of the bis(2-phenylpyridinato-)(2,2'-bipyridine) iridium(III) ion ([Ir(ppy)(2)(bpy)](+)), used as a photosensitizer in photocatalytic water splitting, by triethylamine was studied by means of UV/VIS, XANES, and EPR spectroscopies, supported by theoretical calculations at density functional theory (DFT) and complete active space self-consistent field (CASSCF/CASPT2) levels. The combination of these methods suggests a predominant bpy localization of the spin-density of the unpaired electron with notable delocalization to the Ir center. This is particularly evident from EPR and theoretical results and leads to broad EPR lines and a large anisotropy of the g-factor.