Highly efficient red fluorescent dyes for organic light-emitting diodes

Abstract

Two red color luminescent dyes, 4-(dicyanomethylidene)-2-tert-butyl-6-(2-(1-(4-tert-butylphenyl)-1,2,3,4-tetrahydroquinolin-6-yl)vinyl)-4H-pyran (OJ1) and 4-(dicyanomethylidene)-2-tert-butyl-6-(2-(1-(4-tert-butylphenyl)-2,3-dihydro-2-methylindolin-5-yl)vinyl)-4H-pyran (OJ2), were synthesized readily in high yields and were used in the fabrication of organic light-emitting diodes (OLEDs). The physical properties of these materials are fully investigated in this report. Their structures are analogous to the well-known red dye, 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), yet with better electrostability. A typical device made with OJ2 doped 1% in aluminium tris(8-hydroxyquinolinate) (Alq₃) displayed a red light with a narrow bandwidth (fwhm 72 nm) at λ_max 615 nm corresponding to a CIE coordinate (0.62, 0.38). The device can be turned on at 3.5 V, and reaches a luminance intensity of 43 400 cd m at ca. 20 V. It shows a luminance efficiency of 6.46 cd A⁻¹, a power efficiency of 2.04 lm W⁻¹, and an external quantum efficiency of 3.27%. The performances of devices are tunable either by adjusting the doping concentrations or by changing the device configurations.