Insights on isomeric emitters with thermally activated delayed fluorescence: Comparison between solvent and crystal state.

Thermally activated delayed fluorescence (TADF) molecules with aggregation-induced emission (AIE) properties have attracted great attention in recent studies. In this study, three isomeric emitters DPAC-4PYPM, DPAC-TRZ and DPAC-6PYPM with TADF are studied in toluene and crystal with the combination of polarizable continuum model (PCM) and quantum mechanics and molecular mechanics (QM/MM) method. Results show that tiny difference of intramolecular interaction is induced due to the variation in the acceptor group, thus similar geometries and stacking patterns in crystal are obtained for three molecules. Our calculation also indicates that the energy diagram is quite different for three molecules in both toluene and crystal state, while the participation of higher triplet excited states provide additional decay channels for the reverse intersystem crossing (RISC) process, which favors the generation of TADF. In addition, the bending vibrations of the phenyl in the donor and the stretching vibrations of the C=C and C-H bonds are suppressed due to the intermolecular interactions in crystal state, thus block the excited-state energy consumption pathway. It indicates that all three molecules are typical AIE systems. Our calculation results agree with experimental measurements and provide more useful information for TADF emitters with AIE properties.