Highly efficient near ultraviolet organic light-emitting diode based on a meta-linked donor-acceptor molecule

A novel near ultraviolet (NUV) emitter with a meta-linked donor-acceptor (D-A) structure between triphenylamine (TPA) and phenanthroimidazole (PPI), mTPA-PPI, was designed and synthesized. This molecular design is expected to resolve the conflict between the non-red-shifted emission and the introduction of a charge-transfer (CT) state in the D-A system, aiming at NUV organic light-emitting diodes (OLEDs) with high-efficiency and colour-purity. Theoretical calculations and photophysical experiments were implemented to verify the unique excited state properties of mTPA-PPI. The mTPA-PPI device exhibited excellent NUV electroluminescence (EL) performance with an emission peak at 404 nm, a full width at half maximum (FWHM) of only 47 nm corresponding to a CIE coordinate of (0.161, 0.049), and a maximum external quantum efficiency (EQE) of 3.33%, which is among the best results for NUV OLEDs. This work not only demonstrates the promising potential of mTPA-PPI in NUV OLEDs, but also provides a valuable strategy for the rational design of NUV materials by using the meta-linked D-A architecture.