CN-modified imidazopyridine as a new acceptor of thermally activated delayed fluorescent emitter.

Two efficient thermally activated delayed fluorescent (TADF) emitters were developed utilizing CN-modified imidazopyridine as an acceptor unit. The CN-modified imidazopyridine acceptor was combined with either an acridine donor or a phenoxazine donor through a phenyl linker to produce two TADF emitters of Ac-CNImPy and PXZ-CNImPy. The acridine donor based Ac-CNImPy emitter exhibited sky blue emission with a CIE coordinate of (0.18, 0.38), while the phenoxazine donor based PXZ-CNImPy showed greenish-yellow emission with a CIE coordinate of (0.32, 0.58). High photoluminescence quantum yield of 80% was observed for the PXZ-CNImPy emitter compared to 40% of the Ac-CNImPy emitter. Organic light emitting diode based on the PXZ-CNImPy emitter demonstrated high external quantum efficiency of 17.0%. Hence, the CN-modified imidazopyridine unit can be considered as useful electron acceptor for the future design of highly efficient TADF emitters.