Px-VPN has a similar structure to 2CzPN with two electron-withdrawing nitrile groups at 1,2-positions and two electron-donating N-phenylphenoxazine groups 4,5-positions of the benzene ring. The phenyl groups separating the electron-donating phenoxazine and electron-withdrawing phthalonitrile are acting as π bridges to the structure of A-π-D. Phenoxazines are stronger electron donating than carbazoles, Px-VPN is a TADF green emitter (λmax PL = 540 nm) while Cz-VPN is blue (λmax PL = 450 nm).
With a smaller ΔEST, the delayed emission lifetime of the green-emitting Px-VPN film found to be much shorter than those of the blue-emitting Cz-VPN, suggesting a more efficient T1 to S1 up-conversion. TADF green light-emitting device based on Px-VPN as the dopant and mCP as the host achieved a high EQE of 14.9%.