Computational Screening of Photodynamics of Transition-Metal Complexes

The design of photoactive compounds is challenging due to the complicated nature that the ensuing photodynamics can assume. The complexity of this problem increases with the size and flexibility of the system, and the challenge becomes especially difficult in the rational design of open-shell transition-metal complexes where many electronic states and nuclear degrees of freedom participate in the excited-state dynamics. The only alternative is then to screen larger numbers of compounds as is done in the present work using computer simulations for a class of near-infrared emitting vanadium(III) complexes. Starting from the mechanism of the known emitter VCl_3(ddpd) (ddpd = N,N'-di\-meth\-yl-N,N'-di\-py\-ri\-di\-ne-2-yl\-py\-ri\-di\-ne-2,6-diamine), we establish design principles including an increase in the ligand-field strength in the complex in order to achieve higher emission quantum yields. Based on these principles, we design a large set of complexes that are tested for larger ligand-field splitting in static quantum chemistry calculations. For the subset of complexes with increased ligand-field splitting, we then perform nonadiabatic dynamics simulations and identify two promising near-infrared emitter with potential similar or increased emission quantum yield compared to the VCl_3(ddpd) reference. An analysis of the mechanisms of all studied complexes reveals individual relaxation pathways for each compound, confirming the difficulty of the identifying useful rational design principles in these photoactive open-shell transition-metal complexes.