Delayed room temperature phosphorescence enabled by phosphines

Abstract

Organic ultralong room-temperature phosphorescence (RTP) usually emerges instantly and immediately decays after excitation removal. Here we report a new delayed RTP that is postponed by dozens of milliseconds after excitation removal and decays in two steps including an initial increase in intensity followed by subsequent decrease in intensity. The delayed RTP is achieved through introduction of phosphines into carbazole emitters. In contrast to the rapid energy transfer from single-molecular triplet states (T₁) to stabilized triplet states (T_n*) of instant RTP systems, phosphine groups insert their intermediate states (T_M) between carbazole-originated T₁ and T_n* of carbazole-phosphine hybrids. In addition to markedly increasing emission lifetimes by ten folds, since T_M → T_n* transition require >30 milliseconds, RTP is thereby postponed by dozens of milliseconds. The emission character of carbazole-phosphine hybrids can be used to reveal information through combining instant and delayed RTP, realizing multi-level time resolution for advanced information, biological and optoelectronic applications.