Fusing Multi-Resonance Framework with Platinum(II) Complex via Cyclometalation for Narrowband Blue TADF

Multi-resonance (MR)-type emitters based on B- and N-embedded polyaromatic hydrocarbons are among the most promising candidates for ultrapure organic light-emitting diodes (OLEDs), owing to their high photoluminescence quantum yields and narrow emission spectra. However, their application as nonsensitized thermally activated delayed fluorescence (TADF) emitters is hindered by long emission lifetimes. Herein, we describe an approach to improving blue MR-TADF emissions by incorporating a DBANA-derived framework into Pt(II) complexes via cyclometalation. By judiciously combining the framework with an N-heterocyclic carbene to form bidentate chromophoric ligands, the MR-B/N core still dominates the lowest-lying singlet and triplet excited states of the resulting Pt(II) complexes. The Pt-modified MR emitters exhibit efficient blue emissions with peaks at approximately 460 nm and a full width at half-maximum of < 30 nm. The incorporation of the Pt atom shortens the delayed fluorescence lifetime to 5.0-11.4 µs. OLEDs based on selected Pt(II) complexes show pure blue electroluminescence with emission maxima at 456 nm and CIE_y values of 0.15-0.17, accompanied by reduced efficiency roll-off compared to the purely organic MR-B/N analogue. This study demonstrates a promising strategy for narrowband blue TADF emitters by merging MR excited-state character with the heavy-metal effect via bidentate chelation.