Engender Persistent Organic Room-Temperature Phosphorescence by Trace Ingredient Incorporation

The trace impurities in pure organic phosphors were always ignored because the ultra-low content impurities were considered to hardly affect the luminescent properties. Evidences from corresponding reports and research have shown that impurities may greatly affect room temperature phosphorescence (RTP) in some crystalline compounds. To date, very few literatures have clearly study the role of impurities in RTP because of the difficulty in the separation and structure identification of impurities. Also no reports have focused on utilizing trace impurities to form new strategies for efficient RTP.

For the first time, an impurity was isolated from 1-(4-bromophenyl)-1H-imidazole (1BBI) and structural identified, which was proved to be the key to RTP in 1BBI crystal. Neither purified impurity nor 1BBI matrix shown any detectable RTP. The impurity could light up the unusual ultralong RTP in matrix even at 0.01 mol% content. Inspired by impurity/matrix phosphorescence, a trace-ingredient-mediated bicomponent strategy was introduced for high phosphorescence quantum yield (QY, up to 74.2%) and extralong lifetime (up to 430 ms).

Research Highlights of this work are including

1. The study of impurities in organic luminescent materials, including phosphorescent materials, is rarely reported due to the great difficulty of separation, purification and structure characterization. This work not only separated, purified and structure identified the trace impurity in the system but also confirmed the fact that the impurity engenders the RTP. And the corresponding mechanism was proposed as well.

2. Inspired by the role of impurities in RTP, this work proposed an effective strategy for the design and preparation of persistent organic RTP based on active ingredient incorporation. Seven compounds were screened out to conduct the bicomponent RTP system and achieved bright RTP with high QY (up to 74.2%) and extra-long lifetime (up to 430 ms)) RTP with tunable colors.

3. Combining the dual emission of blue fluorescence and yellow phosphorescence, a bicomponent system achieved a bright white-light emission, which shows its outstanding application potential.

The design concept and strategy of this work supplies an efficient approach to develop RTP by simply mixing the matrix with a trace amount of active ingredients. And the trace-ingredient-mediated bicomponent system is preferred for its high efficiency, color-tunable, low cost and easy to prepare properties, which will make important sense for facilely developing organic persistent RTP materials. This work will not only lead to a new understanding of persistent organic RTP but also develop a facile and effective strategy for RTP afterglow materials.