Dual Regulation of Molecular Rigidity and Orbital Engineering of Pt(II) Emitters for High-Performance Deep-Blue OLEDs.

Abstract

Blue phosphorescent organic light-emitting diodes (PhOLEDs) face critical challenges in terms of low color purity and severe efficiency roll-off. In this study, four novel tetradentate Pt(II) emitters (PtCY, PtCY-F, PtCY-tBu, PtCY-tBuF) are designed through a synergistic strategy of molecular orbital engineering and steric hindrance effect. By introducing a bulky diisopropylbiphenyl (diPrPh) group at the N-heterocyclic carbene (NHC) moiety to increase molecular rigidity and suppress intermolecular interactions, the Pt(II) emitters achieve narrowband deep-blue emission (452-457 nm) in dichloromethane, with full width at half maximum (FWHM) values of 18-23 nm. Combined with the introduction of fluorine atoms (─F) away from the lowest unoccupied molecular orbital (LUMO) distribution, the external quantum efficiency (EQE) is improved while avoiding the breakage of the C─F bond. PtCY-tBuF-based device B4 achieved a high maximum luminance of 45621 cd m^-2, and record high EQEs of 27.1%, 24.3%, and 21.7% at high brightness levels of 1000, 5000, and 10 000 cd m^{- 2} respectively and lowest efficiency roll-off of 3.2% at 1000 cd m^-2, among reported Pt(II)-based deep-blue OLEDs with CIE_y < 0.15. This study provides a novel strategy for the development of highly efficient tetradentate Pt(II) emitters with high color purity for high-performance deep-blue PhOLED applications.