Electron‐Affinity Substituent in 2,6‐Dicarbonitrile Diphenyl‐1λ5‐Phosphinine Towards High‐Quality Organic Lasing and Electroluminescence under High Current Injection

Abstract

AbstractRationally manipulating the functional substituents plays a crucial role in tuning the luminescence and lasing properties of organic gain media. Herein, a cyanophenyl‐moiety, which exhibits relatively weaker electron affinity, is connected to 2,6‐dicarbonitrile diphenyl‐1λ5‐phosphinine (DCNP) via para‐linking. Resultantly, the appreciated locally‐excited characteristics ensuring a large oscillator strength and high radiative rate can be reserved in DCNP‐4‐(4‐cyanophenyl) (DCNP‐pCN). Interestingly, the weak charge‐transfer state from the relative donor (D)/acceptor (A) interplay enables small singlet‐triplet splitting (ΔEST ≈ 0.45 eV). Thus the triplets generated on DCNP‐pCN can be efficiently scavenged by 4,4'‐bis[(N‐carbazole)styryl]biphenyl (BSBCz), which is used as the host with a lower‐lying triplet energy level for DCNP‐pCN. Moreover, benefitting from the mediation between the conjugated length extension and weak D/A interplay, the emission spectrum cannot be largely shifted, which can effectively suppress the overlap between the lasing emission of DCNP‐pCN and the excited‐state absorption of BSBCz, thereby avoiding detrimental singlet‐triplet annihilation. Thus, high‐quality distributed feedback lasings with ≈2.0 μJ cm−2 thresholds are achieved, and the organic light‐emitting diodes exhibit external quantum efficiency exceeding 2.0% without efficiency rolloff under high current injection, indicating the potential for electrical‐pumping organic lasings.