A DCM‐Type Red‐Fluorescent Dopant for High‐Performance Organic Electroluminescent Devices

Abstract

Abstract 2‐(2‐ tert ‐Butyl‐6‐(( E )‐2‐(2,6,6‐trimethyl‐2,4,5,6‐tetrahydro‐1 H ‐pyrrolo[3,2,1‐ ij ]quinolin‐8‐yl)vinyl)‐4 H ‐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)‐4 H ‐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 (Alq 3 ):dopant (2.3 wt %) (7 nm)/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (BCP; 12 nm)/Alq 3 (45 nm)/LiF(0.3 nm):Al (300 nm), shows a larger maximum luminance ( L max = 6021 cd m –2 at 17 V), higher maximum efficiency (η max = 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 ( L max = 3453 cd m –2 at 15.5 V, η max = 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.