Toward Solution-Processed Deep-Blue OLEDs: Ligand-Core Engineering of Pt(II) Sensitizers

Blue organic light-emitting diodes (OLEDs) remain the bottleneck for both display performance and manufacturing cost, as the simultaneous achievement of high efficiency, deep-blue color purity, and solution processability has proven exceptionally difficult. In particular, achieving deep-blue emission (CIE y < 0.15) with a high external quantum efficiency (EQE) in solution-processed devices has rarely been demonstrated, as most high-performance deep-blue phosphor-sensitized fluorescence (PSF) systems rely on vacuum deposition. Here we report two solution-processable tetradentate Pt(II) sensitizers, PtON-BnNap and PtON-PyNap, which share a naphthylmethyl-substituted imidazole ancillary ligand but differ in their azole core (benzimidazole versus electron-deficient pyrido-imidazole). Both complexes exhibit predominantly ligand-centered (³LC) triplet emission with a triplet energy of 2.72 eV closely matched to the MR-TADF emitter t-Bu-ν-DABNA, while the azole core substitution selectively tunes the LUMO and the excited-state character. Employed as sensitizers in solution-processed PSF-OLEDs with t-Bu-ν-DABNA, both complexes deliver deep-blue electroluminescence at CIE (0.129, 0.111) and (0.130, 0.112) with FWHM of 17 nm and maximum EQEs of 22.3% (PtON-BnNap) and 22.8% (PtON-PyNap). The near-resonant energy alignment and the substantial narrowing of the emission bandwidth confirm efficient energy transfer from the Pt(II) sensitizer to the fluorescent emitter. These results establish ligand-core engineering of ³LC-dominant Pt(II) sensitizers as a viable strategy for efficient, color-pure deep-blue solution-processed PSF-OLEDs.