Transformation from room temperature phosphorescence to TADF enhanced dual emission by aggregation-induced quantum interference

Abstract

Studying the impact of aggregation-induced quantum interference on excited state dynamics is a challenging and critical problem for regulating the emission of room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF). We designed and synthesized TPCO molecules with RTP properties. Additionally, we cultured two crystals with similar molecular arrangements but different luminescence mechanisms: one exhibits monomer-like green RTP luminescence (G-form), and the other shows yellow TADF luminescence (Y-form). Experimental and theoretical studies demonstrate that both G- and Y-form crystals exhibit similar molecular arrangements, specifically an inversion-packed dimer structure. In Y-form crystals, the reduction of intermolecular distances leads to an enhancement of excitonic couplings. The positive singlet and triplet excitonic couplings of the inversion-packed dimer significantly increase the fluorescence transition dipole moment by a -fold factor, corresponding to the degree of aggregation. Additionally, the energy gap (ΔE_ST) decreases from G-form crystals to Y-form crystals. These effects collectively enhance TADF emission. Due to their similar molecular arrangements, the transition between G-form and Y-form aggregates can be readily achieved by applying pressure. The research findings contribute to a deeper understanding of the effects of aggregation on RTP and TADF mechanisms and offer novel design guidance for the development of high-performance smart materials.