Synergistic Generation and Accumulation of Triplet Excitons for Efficient Ultralong Organic Phosphorescence

The traditional method to achieve ultralong organic phosphorescence (UOP) is to hybrid nπ* and ππ* configurations in appropriate proportion, which are contradictory to each other for improving efficiency and lifetime of phosphorescence. In this work, through replacing the electron‐donating aromatic group with a methoxy group and combining intramolecular halogen bond to promote intersystem crossing and suppress non‐radiative transition, an efficient UOP molecule (2Br‐OSPh) has been synthesized with the longest lifetime and brightest UOP among its isomers. As compared to CzS2Br, which has a similar substituted position of bromine atom and a larger kisc (the rate of intersystem crossing), the smaller ΔETT* (the energy gap between monomeric phosphorescence and aggregated state phosphorescence) in 2Br‐OSPh could accelerate the transition from T1 to T1*. This research indicates that both generation and accumulation of triplet excitons play an important role in realizing efficient UOP materials. Based on the synergistic effect of generation and accumulation of triplet excitons, an efficient UOP molecule (2Br‐OSPh), which exhibits a fast rate of intersystem crossing and a small energy gap between monomeric phosphorescence and aggregated state phosphorescence has been synthesized with the longest lifetime and brightest UOP among its isomers.