Isomeric Effects on the Regulation Mechanism for Luminescence Properties of D-A-D Stacked TSCT-TADF Molecules: A Theoretical Perspective

Materials possessing both thermally activated delayed fluorescence (TADF) and through-space charge transfer (TSCT) characteristics exhibit promising application prospects in organic light-emitting diodes (OLEDs) due to their highly efficient exciton utilization capabilities. However, the development of highly efficient TSCT-TADF materials remains a significant challenge. In this study, the photophysical properties of SAF27DCPP and SAF36DCPP molecules in both toluene and crystal phases were investigated using the quantum mechanics/molecular mechanics (QM/MM) method and the thermal vibration correlation function (TVCF) theory. In toluene, an increase in the kr and a decrease in the knr contribute to enhanced photoluminescence efficiency. Furthermore, conformational isomerization leads to significantly different emission efficiencies between the two molecules; the photoluminescence quantum yield (ΦF) of SAF36DCPP is almost twice that of SAF27DCPP, which is primarily driven by the ortho-linkage that increases the transition dipole moment and reduces the reorganization energy. Based on these computational results, we aim to elucidate the relationship between molecular isomerization effects and luminescence performance, thereby providing theoretical guidance for the design and development of highly efficient TSCT-TADF devices.