Understanding the light-emitting mechanism of an X-shape organic thermally activated delayed fluorescence molecule: First-principles study

Highlights: • There are two stable conformers for the ACRSA molecule, and conformer A has lower energy than conformer B. • Conformer B is responsible for the light-emitting of the ACRSA molecule, since conformer A is non-radiative. • Up-conversion happens between the S1 and T1 states. • Out-of-plane vibration modes contribute most to the reorganization energy of S1. The light-emitting mechanism of an X-shape organic thermally activated delayed fluorescent molecule is investigated based on first-principles calculations. It is found that there are two stable configurations for the ACRSA molecule, and that the molecule with conformer A is nonluminous. Further, the excited states dynamics of conformer B is studied. The normal modes analysis of the reorganization energy indicates that the non-radiation process of the first singlet excited state (S1) mainly comes from the out-of-plane vibration with low frequencies. Besides, calculations of energy levels of excited states demonstrate that the up-conversion happens between the S1 and T1 states.