A theoretical study on the effects of intramolecular and intermolecular interactions on excited state properties of two NIR-TADF combined with AIE molecules

Abstract

TADF emitters with both high exciton utilization and luminescence efficiency show promising applications in OLEDs, especially it with AIE characteristics. However, theoretical studies on emitters with amorphous structure with the consideration of the solid-state effect are limited. In this work, a multi-scale simulation is performed to study the reported compounds TBSMCN and O-TBSMCN, which both possess distinct features of NIR-AIE-TADF. The packing modes of the molecules in film and crystal are obtained by molecular dynamics simulations (MD) and experiments, and then the photo physical properties are studied by using the QM/MM method. The results show that geometrical changes between the ground state (S0) and the first singlet excited state (S1) are restricted in aggregate state. Thus, the non-radiative energy consumption process is hindered, this indicates the AIE mechanisms. Second, the molecules exhibit a smaller △ES1-T1 and a more significant SOC in aggregate state, which is more favorable for the RISC. Finally, by analyzing the NTO of the dimers in the film, the O-TBSMCN molecule undergoes intermolecular charge transfer, which may be one of the reasons for the significant reduction in its film efficiency. Our calculations could help one to better understand the NIR-AIE-TADF mechanism from a theoretical perspective.