Platinum Complexes of 4-Hydoxy-1,5-naphthyridines as Emitting Dyes

4-Hydoxy-1,5-naphthyridines (HNt) are derivatives of 8-hydroxyquinolines, yet possess a wider HOMO and LUMO band gap than the latter. The cyclometalated complex of platinum(II) with Nt exists in a square planner geometry, and has a high tendency to aggregate in condensed media. Such a phenomenon was verified by examining its photo-luminescence spectra in different concentrations. In a dilute solution, it exhibits a yellow phosphorescence centered at 530∼555 nm, yet red-shifted to ∼660 nm in a concentrated solution or in the solid state. This series of compounds can be used as emitting dyes in light-emitting diodes (LED). The LED devices with a configuration ITO/NPB/dye (6%) in CBP/BCP/AlQ3 or TPBI/LiF/Al displayed a yellow to red color, where NPB, CBP, BCP, AlQ3 and TPBI denote 4,4′-bis[N-(1-naphthyl),N-phenylamino]biphenyl, 4,4′-bis(carbazol-9-yl)biphenyl, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, tris(8-hydoxyquinolinato)aluminium, and 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole), respectively. The maximal light intensity exceeds 2.6 × 104 cd/m2 with an external quantum efficiency up to 5.8%.