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.