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.