Regulation of\nTADF and RTP Dual Emission via Internal\nand External Heavy-Atom Effects

Organic materials with thermally activated delayed fluorescence\n(TADF) and room-temperature phosphorescence (RTP) dual emission have\nattracted great attention in recent years, but the regulation mechanism\nvia internal and external heavy atoms is not clear enough. Here, we\ncarry out a systematic theoretical investigation on the photophysical\nproperties of the materials by introducing aliphatic or aromatic bromine\natoms. The molecule with aromatic bromine atoms exhibits obvious TADF\nowing to the effective reverse intersystem crossing (RISC) with matchable\nenergy levels and enhanced spin orbit couplings, the molecule with\naliphatic bromine atoms shows a long RTP lifetime because of the reduced\nnonradiative transition of triplet excitons, and the molecule with\nboth aliphatic and aromatic bromine atoms presents balanced TADF and\nRTP emissions thanks to the synergy internal and external heavy-atom\neffects. Besides, the internal and external heavy atoms induce multisite\nintermolecular interactions, effectively suppressing the nonradiative\nprocess in the solid phase. The efficient RISC process and the suppressed\nnonradiative process of triplet excitons should be key to regulating\nthe dual emission property. These findings and insights are of great\nimportance for revealing the structure–performance relationship,\nproviding theoretical guidance for the design of TADF and RTP dual\nemission molecules via internal and external heavy-atom effects.