Luminescent properties of thermally activated delayed fluorescence molecule with intramolecular π–π interaction between donor and acceptor

Influence of intramolecular π–π interaction on the luminescent properties of thermally activated delayed fluorescence (TADF) molecule (3, 5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)-phenyl)(pyridin-4-yl) methanone (DTCBPY) is theoretically studied by using the density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Four conformations (named as A, B, C, and D) of the DTCBPY can be found by relax scanning, and the configuration C corresponds to the luminescent molecule detected experimentally. Besides, we calculate the proportion of each conformation by Boltzmann distribution, high configuration ratios (44% and 52%) can be found for C and D. Moreover, C and D are found to exist with an intramolecular π–π interaction between one donor and the acceptor; the intramolecular interaction brings a smaller Huang–Rhys factor and reduced reorganization energy. Our work presents a rational explanation for the experimental results and demonstrates the importance of the intramolecular π–π interaction to the photophysical properties of TADF molecules. (paper)