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 similar to 555 nm, yet red-shifted to similar 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/AlQ(3) or TPBI/LiF/Al displayed a yellow to red color, where NPB, CBP, BCP, AlQ(3) 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 x 10(4) cd/m(2) with an external quantum efficiency up to 5.8%.