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/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‐1 H ‐benzimidazole), respectively. The maximal light intensity exceeds 2.6 × 10 4 cd/m 2 with an external quantum efficiency up to 5.8%.