Regulation of Thermally Activated Delayed Fluorescence to Room Temperature Phosphorescent Emission Channels by Controlling the Excited-States Dynamics via J- and H-Aggregation.

Abstract

Controlling of excited-state dynamics plays a central role in tuning room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) emissions, but remaining challenging in the exploration of organic luminescent materials (OLMs). Herein, we demonstrated the regulation of TADF and RTP emissions of a boron difluoride β- acetylnaphthalene chelate ( β CBF 2 ) by controlling the excited-state dynamics via its J- and H-aggregation states. Two crystalline polymorphs emitting green and red light have been controllably obtained. Although both belong to the monoclinic system, the green and red crystals are dominated by J- and H-aggregation respectively, due to different molecular packing arrangements. Experimental and theoretical studies show that J-aggregation not only significantly reduces the energy gap between the lowest singlet and triplet excited states for the realization of ultra-fast reverse intersystem crossing (RISC) process, but also enhances the radiative decay of singlet, together leading to TADF. The H-aggregation accelerates the ISC and meanwhile suppresses the radiative decay of singlet, helping to stabilize the triplet exciton for RTP. These results deepen the understanding of the effect of aggregation on the luminescence mechanism of organic solids, and provide new strategy to tuning TADF and RTP OLMs.