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Keywords:

  • Doping;
  • Electroluminescence;
  • Light-emitting diodes, organic;
  • Organic electronics;
  • Red-light emitters

Abstract

2-(2-tert-Butyl-6-((E)-2-(2,6,6-trimethyl-2,4,5,6-tetrahydro-1H-pyrrolo[3,2,1-ij]quinolin-8-yl)vinyl)-4H-pyran-4-ylidene)malononitrile (DCQTB) is designed and synthesized in high yield for application as the red-light-emitting dopant in organic light-emitting diodes (OLEDs). Compared with 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7,-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), one of the most efficient red-emitting dopants, DCQTB exhibits red-shifted fluorescence but blue-shifted absorption. The unique characteristics of DCQTB with respect to DCJTB are utilized to achieve a red OLED with improved color purity and luminous efficiency. As a result, the device that uses DCQTB as dopant, with the configuration: indium tin oxide (ITO)/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB; 60 nm)/tris(8-quinolinolato) aluminum (Alq3):dopant (2.3 wt %) (7 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP; 12 nm)/Alq3(45 nm)/LiF(0.3 nm):Al (300 nm), shows a larger maximum luminance (Lmax = 6021 cd m–2 at 17 V), higher maximum efficiency (ηmax = 4.41 cd A–1 at 11.5 V (235.5 cd m–2)), and better chromaticity coordinates (Commission Internationale de l'Eclairage, CIE, (x,y) = (0.65,0.35)) than a DCJTB-based device with the same structure (Lmax = 3453 cd m–2 at 15.5 V, ηmax = 3.01 cd A–1 at 10 V (17.69 cd m–2), and CIE (x,y) = (0.62,0.38)). The possible reasons for the red-shifted emission but blue-shifted absorption of DCQTB relative to DCJTB are also discussed.