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

Abstract

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),Nphenylamino]biphenyl, 4,4¢-bis(carbazol-9-yl)biphenyl, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, tris(8-hydoxyquinolinato)aluminium, and 2,2¢,2²-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole), respectively. The maximal light intensity exceeds 2.6 × 10 4 cd/m 2 with an external quantum efficiency up to 5.8%.

Synthetic Strategies, Reactivity and Applications of 1,5-Naphthyridines

“…Gould-Jacobs reaction, reported by Brown and Dewar in 1978 [ 17 ], between 3-aminopyridine 7 and diethyl methylenemalonate 8 followed by a thermal cyclization afforded the 1,5-naphthyridine 9a ( Scheme 3 ) [ 18 ]. 4-Hydroxy-1,5-naphthyridine 9b was also prepared by a condensation reaction at 150 °C followed by a ring cyclization to yield the 1,5-naphthyridine skeleton ( Scheme 3 ) [ 19 ]. Similarly, 1,5-naphthyridine derivative 10a has been obtained [ 20 ].…”

“…Heteroleptic platinum(II) complexes bearing two ligands, hydroxynaphthyridine and 2-(2,4-difluorophenyl)pyridine, were synthesized in two steps [ 19 , 113 ]. The first ligand 251 was attached by treatment with K 2 PtCl 4 to form platinum dichloride-bridged dimer 252 , followed by reaction with naphthyridinol derivatives 19a , b (previously prepared, vide supra, Scheme 6 ) or 253a , b as second ligand in 2-ethoxyethanol to yield complexes 254 ( Scheme 101 ).…”

“…Therefore, the color of these devices could be tuned from yellow to red by adjusting the doping concentrations. For this reasons, this series of compounds can be used as emitting dyes in light-emitting diodes (LED) [ 19 ]. Some heteroleptic platinum (II) complexes with 4-hydroxy-1,5-naphthyridine ligands 254 (previously prepared, vide supra, Scheme 101 ) were used for the construction of WOLEDs with multilayer structures ( Figure 36 ) [ 33 , 113 , 142 ].…”