From Structure to Function: Designing Iridium Catalysts with Spin-Forbidden Excitation for Low-Energy Light-Driven Reactions

Herein we describe a comprehensive study of ligand effects on optoelectronic properties of a series of Ir(III) catalysts which undergo formally spin-forbidden excitation using low-energy light. We demonstrate that electronic and steric tuning of several variables can be explained by their impact on the HOMO and LUMO energies of the complex. Density functional theory calculations of the catalysts' adiabatic triplet energies agree with the experimental results to within 0.05 eV on average. As many of these subtle effects are independent of each other, the merger of them in a single complex tends to have an additive effect and we thus succeeded in developing a family of highly oxidizing iridium photocatalysts that operate by spin-forbidden excitation.