On the In Silico Evaluation of the Emission Quantum Yield of Cyclometalated Ir(III) Complexes

The in silico determination of the emission quantum yield (Φ_em) of a cyclometalated Ir(III) complex requires the evaluation of all its possible radiative and nonradiative decays. The task is challenging, particularly when more than one minimum is present on the potential energy surface of the emitting lowest-energy triplet T₁, a situation more common than what was previously thought. In the present contribution, we study all possible radiative and nonradiative paths for the two cyclometalated Ir(III) complexes, [Ir(ppy)₂(pyim)]⁺ and [Ir(diFppy)₂(dtb-bpy)]⁺, indeed characterized by T₁ minima of both metal-to-ligand charge transfer and ligand-centered nature. Comparing the computed emission quantum yields accounting for all processes and for only those processes in principle more relevant, we aimed at judging the importance of characterizing all decays to provide an accurate estimation of Φ_em. Evaluating the barrier between emitting T₁ and nonradiative ³MC states obtaining the corresponding transition state or approximating the latter using the CI-NEB method, we aimed at judging the importance of performing transition state optimizations. The latter task, due to its intrinsic complexity and poor convergence behavior, is a bottleneck for the characterization of the photophysics of a complex and consequently prevents a more efficient screening of cyclometalated Ir(III) complexes for technological applications.