Effect of intermolecular interaction on excited-state properties of thermally activated delayed fluorescence molecules in solid phase: A QM/MM study.
Recently, thermally activated delayed fluorescence (TADF) molecules have attracted great attention since nearly 100% exciton usage efficiency was obtained in TADF molecules. Most TADF molecules used in organic light-emitting diodes are in aggregation state, so it is necessary to make out the intermolecular interaction on their photophysical properties. In this work, the excited-state properties of the molecule AI-Cz in solid phase are theoretically studied by the combined quantum mechanics and molecular mechanics (QM/MM) method. Our results show that geometry changes between the ground state (S0) and the first singlet excited state (S1) are limited due to the intermolecular π-π and CH-π interactions. The energy gap between S1 and the first triplet excited state is broadened and the transition properties of excited states are changed. Moreover, the Huang-Rhys factors and the reorganization energy between S0 and S1 are decreased in solid phase, because the vibration modes and rotations are hindered by intermolecular interaction. The non-radiative rate has a large decrease in solid phase which improves the light-emitting performance of the molecule. Our calculation provides a reasonable explanation for experimental measurements and highlights the effect of intermolecular interaction on excited-states properties of TADF molecules.
['Zhang|Kai|K|', 'Cai|Lei|L|', 'Fan|Jianzhong|J|', 'Zhang|Yuchen|Y|', 'Lin|Lili|L|', 'Wang|Chuan-Kui|CK|']
Intermolecular interactions Thermally activated delayed fluorescence Hybridized local and charge transfer state QM/MM method