Host to regulate the T1–S1 and T1–S0 processes of guest excitons in doped systems to control the TADF and RTP emissions

Abstract

It has been a challenge to tune the T₁ to S₁ and T₁ to S₀ processes of excitons to combine thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) emissions to realize the diversification of afterglow phenomena in organic materials. Herein, a guest is designed and four hosts with different energy levels are selected to construct an organic host–guest system. The hosts can promote the intersystem crossing (ISC)/reverse intersystem crossing (RISC) efficiencies of guest excitons efficiently, which results in almost only RTP and TADF emissions of the doped materials, but no prompt fluorescence emission. Importantly, the different energy levels of the hosts can further regulate the proportion of excitons in TADF and RTP, so that the two emissions can be combined into a wide range (498–571 nm) of new delayed emission wavelengths, and the afterglow colors of the doped materials also gradually red-shift from the cyan of TADF to the yellow-orange of RTP. Additionally, since the lifetime of TADF is greater than that of RTP, the doped materials show an anomaly phenomenon that the prompt wavelengths are longer than the delayed wavelengths; in layman's terms, the color of “Turn On” is redder than that of “Turn Off”.