A novel reddish-orange-emitting cationic iridium(III) complex containing a carbazole-triazine bipolar unit: Synthesis and application in neutral/warm white light-emitting diodes

Abstract A reddish-orange-emitting cationic iridium(III) complex [(dfppy)2Ir(EPTC)]PF6 (dfppy: 2-(2,4-difluorophenyl)pyridine, EPTC: 9-ethyl-3-(3-(pyridin-2-yl)-1,2,4-triazin-5-yl)-9H-carbazole) containing a carbazole-triazine bipolar unit was synthesized. The thermal decomposition temperature (Td) of the complex was 355 °C, its relative emission intensity at 100 °C was 78.6% of that at 20 °C, which was enough for it to be used in LEDs. Mainly due to the bipolar unit, [(dfppy)2Ir(EPTC)]PF6 can efficiently absorb and be excited by blue light (λem,max = 457 nm) of GaN chips. Excited by blue-emitting GaN chips, the complex can be used for fabricating reddish-orange LEDs, moreover, together with yellow-emitting Y3Al5O12:Ce3+ (YAG:Ce), neutral and warm white light-emitting diodes (WLEDs) can be obtained with good performances. When [(dfppy)2Ir(EPTC)]PF6 was blended in silicone at 1.0, 1.5 and 2.0 wt% respectively, all together with YAG:Ce at 4.0 wt%, three efficient neutral WLEDs were obtained. Their correlate color temperatures (CCT) were 4874 K, 4312 K and 3665 K, color rendering indexes (CRI) were 80.2, 78.3 and 76.4, luminous efficiencies (ηL) were 88.5 lm·W−1, 83.6 lm·W−1 and 67.4 lm·W−1, Commission International de I'Eclairage (CIE) values were (0.34, 0.32), (0.36, 0.33) and (0.38, 0.33) respectively. When blending concentration of [(dfppy)2Ir(EPTC)]PF6 was increased to 2.5 wt% together with YAG:Ce still at 4.0 wt%, a warm WLED was obtained, its CCT was 3282, CRI was 73.9, ηL was 63.0 lm·W−1, and CIE value was (0.40, 0.35).