High-Purity and Saturated Deep-Blue Luminescence from trans-NHC Platinum(II) Butadiyne Complexes: Properties and Organic Light Emitting Diode Application

Two new platinum­(II) compounds with trans-(NHC)2Pt­(CC–CC–R)2 (where NHC = N-heterocyclic carbene and R = phenyl or trimethylsilyl) architecture exhibit sharp blue-green or saturated deep-blue phosphorescence with high color purity. The photoluminescence of both compounds is dominated by an intense 0–0 band with distinct but weaker vibronic progressions in both tetrahydrofuran (THF) and poly­(methyl methacrylate) (PMMA) matrix. The full width at half-maximum (fwhm) of the photoluminescence of trans-(NHC)2Pt­(CC–CC-trimethylsilyl)2 are 10 nm at room temperature and 4 nm at 77 K, while the trans-(NHC)2Pt­(CC–CC-phenyl)2 shows a fwhm of 14 nm at room temperature and 8 nm at 77 K. The Commission International de L’Eclairage (CIE) coordinates of trans-(NHC)2Pt­(CC–CC-phenyl)2 are (0.222, 0.429) in PMMA, and trans-(NHC)2Pt­(CC–CC-trimethylsilyl)2 has a deep-blue CIE of (0.163, 0.077) in PMMA. When doped into PMMA, the phosphorescence quantum yield of the complex with trimethylsilyl-butadiyne ligand increases dramatically to 57% from 0.25% in THF, while the complex with phenyl-butadiyne ligand has similar quantum yields in PMMA (32%) and THF (37%). Organic light-emitting diodes (OLEDs) employing these two complexes as the emitters were successfully fabricated with electroluminescence that closely matches the corresponding photoluminescence. The OLEDs based on trans-(NHC)2Pt­(CC–CC-trimethylsilyl)2 display highly pure deep-blue electroluminescence (fwhm = 12 nm) with CIE coordinates of (0.172, 0.086), approaching the most stringent National Television System Committee (NTSC) coordinates for “pure” blue of (0.14, 0.08).