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

The traditional method to achieve ultralong organic phosphorescence (UOP) is to hybrid n pi* and pi pi* 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 k(isc) (the rate of intersystem crossing), the smaller Delta E-TT* (the energy gap between monomeric phosphorescence and aggregated state phosphorescence) in 2Br-OSPh could accelerate the transition from T-1 to T-1*. This research indicates that both generation and accumulation of triplet excitons play an important role in realizing efficient UOP materials.