Coumarin Ligands Regulate Excited-State Intersystem Crossing Processes of Ir(III)-Based Transition Metal Complexes

Iridium(III)-based transition metal complexes (TMCs) have attracted much attention due to their excellent photophysical properties (i.e., powerful visible light trapping ability, ultrafast intersystem crossing (ISC) processes, long-lived triplet excited states, etc.) and show promising applications in energy, materials, and biotechnology. The photophysical properties of Ir(III)-based TMCs are highly related to those of their ligands. Revealing the photophysical mechanisms of these Ir(III)-based TMCs is crucial for elucidating the excited-state behavior and regulating the properties of these TMCs. Nonadiabatic dynamics (NAMD) simulations have become powerful tools for elucidating complicated photoinduced processes. In this work, we combine statically excited-state electronic structure calculations with NAMD simulations to reveal the photoinduced dynamics of Ir(III)-based TMCs containing coumarin, phenylpyridine (ppy), and ppy-bodipy (boron dipyrromethene) ligands (referred to as Ir1, Ir2, and Ir3). The calculated absorption peaks are in good agreement with the experimental ones, which confirm the reliability of the selected computational method (TD-B3LYP+D3/def2-SVP). Then, NAMD simulations of Ir1, Ir2, and Ir3 are performed at the same level. Time-dependent populations show that the ISC processes are quite different among these Ir(III)-based TMCs, which can be attributed to the number of coumarin ligands. The coumarin ligands can inhibit the ISC processes between the excited states by decreasing the spin-orbit coupling matrix elements (SOCMEs). This newly proposed insight is validated by two newly designed Ir(III)-based TMCs. Moreover, the electron/hole dynamics and the exciton dynamics are analyzed for elucidating the detailed photoinduced mechanism of Ir(III)-based TMCs. In conclusion, this study provides new insights for the rational design of Ir(III)-based TMCs with controlled photophysical properties through ligand engineering and offers new perspectives for applications in optoelectronics and energy conversion.