上海科技大学知识管理系统

Implanting heteroatoms into organic pi-conjugated molecules (OCMS) offered a great opportunity to fine-tune the chemical structures and optoelectronic properties. This work describes a new family of 1,4-azaphosphinines with extended sigma-pi hyperconjugations. The photophysical studies revealed that azaphosphinines exhibited narrow-band thermally activated delayed fluorescence (TADF) ( full width at half-maximum: 26-40 nm). According to the orbital localization analysis and natural bond orbital analysis, the effective sigma*-pi* hyperconjugation is believed to induce the multiple-resonance (MR) TADF, which is distinct from the p-pi conjugation-induced MR-TADF in BN systems. Although having the large (Delta)E(S1-T1)s (>3.0 ev), the study suggested that sigma*-pi hyperconjugation endowed the system with the structural vibration favorable for the spin-vibronic-assisted RISC. Having the tunable p-centers (lp, O, S, Se, and Me+), azaphosphinines showed a fine-tuned TADF. Generally, azaphosphinines with strong sigma*-pi* hyperconjugations showed small (Delta)E(S1-T1)s, efficient RISCs, and high PLQYs. Leveraging on the efficient hyperconjugations, TADF emission of the system spanned from UV-blue to green. Particularly, extended azaphosphinines exhibited the high photoluminescence quantum yields (74% in toluene and 92% in the 10% doped PMMA). As a proof of concept, two azaphosphinines with a PO center were applied as the light-emitting materials in organic lighting-emitting diodes. The devices showed the narrow-band UV- and deep-blue emission with EQE as high as 10.3%. The current study offered us a new strategy, namely, sigma-pi hyperconjugation-induced MR-TADF, for designing OCMs with tunable light-emitting properties.