Theoretical Studies on Thermally Activated Delayed Fluorescence Mechanism of Au(III) Complexes in Films: Insights from Quantum Mechanics/Molecular Mechanics Simulations

Organometallic complexes usually exhibit thermally activated delayed fluorescence (TADF) emission in films. However, the surrounding effects on TADF have not been explored and the underlying photophysical mechanism remains elusive. In this study, we have investigated structures, spectroscopic characteristics, radiative and nonradiative rates, and luminescence mechanisms of three Au(III) complexes in films using DFT and time-dependent DFT approaches combined with molecular dynamics and quantum mechanics/molecular mechanics simulations. The results show that the S1 and T1 states are of ligand-toligand charge transfer character owing to the efficient separation of the HOMO and the LUMO. Proper spin-orbit couplings and small energy gaps between the S1 and T1 states benefit the reverse intersystem crossing process enabling TADF. Moreover, the film environments play key roles in regulating geometric structures, electronic properties, and thereto luminescence. These results provide insights into understanding the TADF mechanism of organometallic complexes in films.