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

Abstract 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.