Multiresonant Framework‐Perturbed Platinum(II) Complexes Enable Efficient Narrowband Red Phosphorescence Emissions

Abstract While considerable research efforts have been devoted to developing narrowband B,N‐embedded multiple resonance (BN‐MR) emitters, despite the formidable challenge, the design of efficient narrowband red phosphors has been overlooked. Herein, we present a design strategy that perpendicularly integrates BN‐MR frameworks into a weakly emissive tetradentate Pt(II) complex to achieve efficient narrowband phosphors. Accordingly, we synthesized two novel emitters, BCzBN‐PyPt and DPABN‐PyPt. The optimized emitter BCzBN‐PyPt exhibits exceptional performance characteristics: 1) narrowband red emission at 605 nm with a small full‐width at half‐maximum (FWHM) of 35 nm/0.118 eV in toluene, 2) a dramatically shortened exciton lifetime of 1.2 µs (compared to 7.6 µs for the parent complex PhPyPt), and 3) a remarkable photoluminescence quantum yield ( Φ PL ) of 75% in doped films–representing a 4.4‐fold enhancement over PhPyPt ( Φ PL = 17%). Theoretical investigations reveal that the BN‐MR skeleton induces significant electronic perturbation of the singlet state, leading to enhanced transition dipole moments and accelerated radiative decay ( k r = 3.3 × 10 5 s −1 versus 0.1 × 10 5 s −1 for PhPyPt). In optimized OLED devices, BCzBN‐PyPt achieves superior red narrowband electroluminescence with a maximum external quantum efficiency of 22.7%.