TADF Mechanism\nin a Carbene-Copper Emitter: Insights\nfrom the Nuclear Ensemble Simulations

We use the nuclear ensemble approach to study the mechanism\nof\nthermally activated delayed fluorescence (TADF) in a carbene-copper-amide\n(CMA1) emitter. The results obtained for the emitter in the gas phase\nare consistent with previously published surface hopping nonadiabatic\ndynamics simulations for the same system. CMA1 has two excited state\nconformations with distinct excited state dynamics. For both conformations,\nthe intersystem crossing (ISC) from the S<sub>1</sub> state occurs\nvia higher-lying triplets, but the reverse ISC (rISC) can occur exclusively\nin the perpendicular orientation of the ligands, directly between\nthe T<sub>1</sub> and S<sub>1</sub> states. Nonadiabatic mixing with\nhigher triplet states is not required for efficient rISC, but T<sub>1</sub> changes diabatic character significantly along the vibrational\nmodes. Furthermore, we find that the inclusion of the solvent effects\nhas a significant impact on the TADF mechanism, enabling rISC in both\nconformations. The calculated rate constants and lifetimes are within\nan order of magnitude of the experimental values.