N-heterocycle substitution engineering on tetra-coordinated boron framework for high-performance narrow-band bidentate Pt(II) complex phosphor

Organometallic phosphors face growing challenges in achieving high-color purity to fulfill the next-generation ultra-high-definition displays due to their broad-band emission. To address this issue, herein we reported a ligand engineering through changing the pyridine substitution position on the tetra-coordinated boron framework to tune the triplet electron transition process of bidentate Pt(II) complexes for narrow-band emission. PtOBN/PtPBN with the pyridine ring coordinated to the Pt center (Py(Pt)) at the ortho/para-position of the pyridine ring coordinate to the boron atom (Py(B)) give broad-band yellow emission peaking at 564 and 551 nm with FWHMs of 78.5/64.5 nm, respectively, while PtMBN with the Py(Pt) at the meta-position of the Py(B) exhibits a narrow-band bluish-green emission peaking at 487 nm with a FWHM of 46.7 nm. Natural transition orbital analyses indicate that charge transfer and local transition contributions of their emissive states can be tuned simply by changing the substitution position of the Py(Pt) relative to the Py(B) on the tetra-coordination boron framework, experimentally identified by the solvent polarity-dependent PL measurements. In addition, all these Pt(II) complexes can give high photoluminescent quantum yields over 0.70. More importantly, the device based on PtMBN can give a narrow-band electroluminescence emission with a full width at half maximum (FWHM) of 47.9 nm and achieve a maximum external quantum efficiency (EQE) of 24.9%, a maximum current efficiency of 57.2 cd A⁻¹, and a maximum power efficiency of 42.0 lm W⁻¹, respectively, representing the first demonstration of high-performance narrow-band bidentate Pt(II) complex phosphor with both the FWHM <50 nm and the EQE approaching 25%, simultaneously. Therefore, this work should not only provide critical clue for the design of narrow-band Pt(II) complex phosphors, but also represent a significant breakthrough in developing high-performance narrow-band bidentate Pt(II) complex phosphors.