Ligand-centered to metal-centered activation of a Rh(iii) photosensitizer revealed by ab initio molecular dynamics simulations

Abstract

Excited state evolution of the rhodium(III) complex [Rh(III)(phen)₂(NH₃)₂]²⁺ (phen = 1,10-phenanthroline) has been investigated theoretically to gain a better understanding of light-driven activation of high-energy metal centered states. Ab initio molecular dynamics (AIMD) simulations show the significance of asymmetric motion on a multidimensional potential energy landscape around the metal center for activated crossover from triplet ligand centered (³LC) to triplet metal centered (³MC) states on picosecond timescales. Significant entropic differences arising from the structural distributions of the ³LC and ³MC states revealed by the simulations are found to favor the forward crossover process. Simulations at different temperatures provide further insight into the interplay between structural and electronic factors governing the ³LC → ³MC dynamics as a concerted two-electron energy transfer process, and the broader implications for photoinduced generation of high-energy ³MC states of interest for emerging photocatalytic applications are outlined.