Carbonyl Functionalized Azaphosphinine-Based Multiple-Resonance Emitters via Regulated p/n/σ-π Hybrid Conjugation

Doping heteroatoms with non-typical electronic couplings offered the great opportunity to fine-tune chemical structures and optoelectronic properties of organic π-conjugated molecules (OCMs). Herein, we reported the first example of hybrid COPN multiple-resonance (MR) thermally activated delayed fluorescence (TADF) emitters via the modular protocols. Compared with the classical BN/CON MR-emitters having p-π conjugation, new COPN MR-emitters maintained the various n/σ/σ*-π* hyperconjugation via the P-center. Collaboratively with CO group, the P-regulated (lp, O, S, and Me⁺) hyperconjugation maintained the strong impacts on the TADF properties, such as FWHM, ISC/RISC, and PLQY. The dominating short-range (SR) N➞CO charge-transfer (CT) character suggested the CON-type MR structure in the PO-derivative. The strong long-range (LR) P➞CO CT character suggested the COP-type MR structure in the P(III)-derivative. Leveraging on the self-amplified PO-hyperconjugation, the double-PO derivative exhibited the dominating PON-type MR-TADF involving the SR N➞PO CT. The increased PLQYs (54%) and narrowed emission (FWHM: 13 nm) are among the best CON-type MR-emitters in the literature. As a proof of concept, the 1^st generation hybrid MR-emitters were applied as the light-emitting materials in organic lighting-emitting diodes that showed the narrow-band blue (FWHM: 26 nm) and cyan emission (FWHM: 17 nm) with EQE as high as 7.3% and 22.8%, respectively. The current study revealed that installing the new hybrid conjugation, namely p/n/σ-π coupling into OCMs holds a great promise for designing new types of MR-emitters with excellent TADF characters.