Platinum Complexes of 4-Hydoxy-1,5-naphthyridines as Emitting Dyes Ching-Ting Chien, a Jin-Ruei Shiu, b Chih-Ping Chang, a Yung-Son Hon, b Duo-Fong Huang, a Po-Ting Chou, c Ching-Yang Liu d and Tahsin J. Chow a,c, * a Institute of Chemistry, Academia Sinica, Nankang, Taipei, Taiwan 115, R.O.C. b Department of Chemistry and Biochemistry, National Chung Cheng University, Chia-Yi, Taiwan 621, R.O.C. c Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, R.O.C. d Department of Applied Chemistry, Chinese Culture University, Taipei 111, Taiwan, R.O.C. (Received: Nov. 18, 2011; Accepted: Jan. 18, 2012; Published Online: Feb. 8, 2012; DOI: 10.1002/jccs.201100671) 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 ver- ified by examining its photo-luminescence spectra in different concentrations. In a dilute solution, it ex- hibits a yellow phosphorescence centered at 530~555 nm, yet red-shifted to ~660 nm in a concentrated so- lution 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 dis- played 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-phenanthro- line, tris(8-hydoxyquinolinato)aluminium, and 2,2¢ ,2²-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimid- azole), respectively. The maximal light intensity exceeds 2.6 × 10 4 cd/m 2 with an external quantum effi- ciency up to 5.8%. Keywords: Platinum complexes; 4-Hydoxy-1,5-naphthyridines; Phosphorescence; OLED; Broad band emission. INTRODUCTION The high triplet emission of platinum complexes has been used effectively in the fabrication of light-emitting di- odes (LEDs). 1,2 The platinum complexes form a square pla- nar geometry around the metallic center, that renders them easier to stack together in condense media. Upon photo-ex- citation, the emissions of both the monomer and the aggre- gate display together forming a broad band spectrum. For- rest and Thompson et al. have taken advantage of the broad band emission of platinum complexes for the fabrication of white light LED devices. These type of devices may find useful applications on illumination. Platinum complexes coordinated to either a phenyl- pyridine (PPy) ligand or a 8-hydroxyquinoline (HQ) ligand have been known for some time. 3,4 The emission from com- plex Pt(PPy)Q (679 nm) displayed a red color due to the quinoline ligand. By replacing the C(4) atom of HQ with a nitrogen, the HOMO-LUMO band gap of 4-hydoxy-1,5- naphthyridine (HNt) is substantially increased. The emis- sion maximum of Pt(PPy)Nt (1a) (555 nm, Fig. 1) is blue- shifted 124 nm with respect to that of Pt(PPy)Q. The emis- sion colors of these materials, i.e., 1a~d, are variable de- pending on the doping concentrations. Their characteristics are investigated in this report. EXPERIMENTAL Instrumentation Absorption spectra were taken on a Hewlett-Packard 8453 spectrophotometer and emission spectra on a Hitachi F-4500 fluorescence spectrophotometer. Infrared spectra were taken on a Perkin-Elmer L118-F000 FT-IR spectrom- eter. 1 H and 13 C NMR spectra were recorded on a Bruker AMX400 super-conducting FT NMR spectrometers. The signals of tetramethylsilane at d 0.00 ppm was used as an internal standard for both 1 H and 13 C NMR spectra. Mass J. Chin. Chem. Soc. 2012, 59, 357-364 © 2012 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 357 JOURNAL OF THE CHINESE CHEMICAL SOCIETY Article Dedicated to the memory of Professor Yung-Son Hon (1955–2011). * Corresponding author. E-mails: tjchow@chem.sinica.edu.tw and cheysh@ccu.edu.tw