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

Rationally 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 (ΔE_ST ≈ 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.