Invisible Room-Temperature Phosphorescence from Highly Symmetric Donor-Acceptor-Donor Organic Materials

Organic emitters with room-temperature phosphorescence (RTP) are of great significance for realizing high photoluminescence quantum yield (PLQY) and tunable color and lifetime of afterglow in the field of organic functional materials, especially for pure organic donor–acceptor–donor (D-A-D) materials. The goal is to endow pure organic materials with tunable color and lifetime, thus expanding their applications in optoelectronics, information display, anticounterfeiting, and encryption. In this paper, we rationally designed three invisible RTP emitters, namely, 2p-SDBTh, 4p-SDBTh, and 4m-SDBTh, by adjusting the substitution position of dibenzo(b,d)thiophene (DBT) moieties as donors connecting to the diphenyl sulfone (DPS) as acceptor. The twisted angles between DBT donor and the phenyl groups of DPS acceptor significantly contributed to photophysical behavior. Temperature-dependent spectroscopic measurements further revealed the “invisible” delayed fluorescence and RTP. This study provides a strategy to finely and symmetrically regulate the donor–acceptor linkage sites in isomeric systems through symmetric modulation of substituted positions, boosting the ISC process.