Ultralong afterglow enabled by energy relay from room-temperature phosphorescent matrixes to local dipoles

Long-persistent afterglows based on organic donor-acceptor systems feature ultra-long duration reaching hours, leading to the advantages in long-time-range display and bio/medical applications. However, the understanding of this optical phenomenon is insufficient. Herein, dibenzothiophene-phosphine oxide hybrids named nDBTxPO with different room temperature phosphorescence characteristics are used as acceptor matrixes. It shows that after doping N,N,N',N'-tetramethylbenzidine (TMB) as donor, afterglow intensities and durations of nDBTxPO:1% TMB are strongly correlated to the stabilized triplet state (T_n*) properties of nDBTxPO. Compared to other congeners, high-population and high-lying T_n^* state of 28DBTDPO matrix supports the positive and efficient energy transfer to ⁿCT^* states of 28DBTDPO-TMB local dipoles in the doped film. This energy relay between two long-persistent T_n^* and ⁿCT^* states is the key determinant resulting in the longest afterglow of 28DBTDPO:1% TMB. This work provides clear insight into energy transfer for lightly-doping donor-acceptor systems, therefore will promote the accurate system design for practical applications.