Activating Intersystem Crossing and Aggregation Coupling by CN-Substitution for Efficient Organic Ultralong Room Temperature Phosphorescence

Organic ultralong room-temperature phosphorescence (OURTP) has boomed recent advances of organic optoelectronics with the significant breakthrough in facilitating the intersystem crossing and stabilization of triplet excitons of purely organic materials. However, it remains a challenge in revealing the inherent mechanism of OURTP and the general molecular design principles of OURTP materials have yet to be reached, largely owing to the rather complicated and varied OURTP molecular structures. Here, we propose a facile strategy to design efficient OURTP materials by simply introducing a cyano group (CN) on benzene. On the basis of these very simple OURTP molecules, it was found that the simultaneously enhanced intersystem crossing and aggregation coupling are two intrinsic prerequisites in realizing the efficient OURTP. The first observation of the excimer emission from the stabilized singlet excited states offers an important evidence for the mechanism study of OURTP, and the direct CN substitution on the benzene ring would be highly instructive for designing efficient OURTP molecules.