Time-Resolved and Blue-Shifted Pure Room-Temperature Phosphorescence by Dynamic Isolation of Triplet Exciton in Crystal

Abstract

Organic room-temperature phosphorescence (RTP) with rich photophysical properties has attracted great interest, but it remains a big challenge to realize pure RTP without fluorescence in steady-state photoluminescence (SSPL) and blue-shifted RTP that intrinsically restricted by the spin-forbidden intersystem crossing (ISC) and the radiative decay of the low-lying triplet excited state. Herein, two fluorescence-free RTP molecules based on β-diketone-bridged phenoselenazine/phenothiazine are developed, which contain either Se or S heteroatom in the phosphor to significantly promote ISC; and, both isolated and J-aggregated phosphors are formed in crystal, where the J-aggregation can not only facilitate the ISC for pure RTP but also strength the emission for high phosphorescent quantum yield of 22.3%, while the isolated phosphor affords longer RTP lifetime up to 131 ms. Excitingly, blue-shifted (35 nm compare to SSPL) pure RTP from yellow-green (525 nm) to cyan (490 nm) that dynamically depending on the time and temperature is observed for the first time. Experimental and theoretical results indicate that the regulation of time/temperature-dependent RTP is attributed to the different lifetimes of the isolated and aggregated emission owing to the dynamic competition between different accumulation modes of phosphors in crystal aided by the interrupted conjugation by the sp³ C of β-diketone.