The role of spin-orbit coupling and state-crossing topography in the non-radiative decay of Ir(III) complexes

TL;DR

This paper challenges the traditional view that triplet metal-centered states solely determine non-radiative decay in Ir(III) complexes, highlighting the importance of spin-orbit coupling and crossing topography in influencing decay rates.

Contribution

It introduces a new perspective emphasizing spin-orbit coupling and crossing topography effects over energy separation in non-radiative decay mechanisms.

Findings

Strong spin-orbit coupling reduces non-radiative decay rates.

Sloped crossing topography affects energy separation between states.

Metal-centered states influence excited state trapping.

Abstract

A pillar of our current understanding of the photoluminescence of Ir(III) complexes is the assumption that the population of triplet metal-centered states determines an efficient non-radiative decay to the ground state minimum. Based on that assumption, the energy separation between the emitting state and the minimum-energy crossing point of the triplet metal-centered and the ground states has been employed as a key variable for evaluating the ability of Ir(III) complexes to decay non-radiatively. We demonstrate that the strong spin-orbit coupling between the triplet metal-centered and the ground state of Ir(III) complexes, together with the sloped topography of their crossing, lead to a significant energy separation between the two states, resulting in a reduced rate of non-radiative ground state recovery. Therefore, we propose that the role of metal-centered states is defined by the tendency of the excited state population to remain trapped in the metal-centered minima.