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

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 × 10⁵ s^-1 versus 0.1 × 10⁵ s^-1 for PhPyPt). In optimized OLED devices, BCzBN-PyPt achieves superior red narrowband electroluminescence with a maximum external quantum efficiency of 22.7%.