Excimer emission from a novel ethyne-based fluorescent dye in organic light-emitting devices

A novel ethyne-based fluorescent dye, 10-(4-Dimethylamino-phenyl ethynyl)-anthracene-9-carbonitrile (DMAPEAC), emitting orange/red light was employed as the light emission layer in organic light-emitting devices (OLED). The absorption and photoluminescence (PL) peak of DMAPEAC dispersed in methylene chloride were measured to be 480 nm and 600 nm, respectively. On the other hand, DMAPEAC (3 wt.%) dispersed in tris(8-hydroxyquinoline) aluminum (Alq₃) films deposited on fused silica exhibited two PL peaks at 600 nm and 630 nm. The extra PL peak at 630 nm was shown to be due to the excimer formation by absorption measurement. An OLED device with trilayer structure using N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)- 4,4′-diamine (TPD) as the hole transport layer, Alq₃ doped with DMAPEAC as the emission layer, 2,9-dimethyl-4,7-diphenyl-1, 10-phenanthroline (BCP) as the hole-blocking and electron-injection layer, and lithium fluoride (LiF)/aluminum (Al) as the cathode. A strong exciton energy transfer from Alq₃ to DMAPEAC was observed as revealed by the electroluminescence (EL) and PL spectra. Maximum brightness of 19,400 cd/m² was obtained at 16 V for the device with 1% DMAPEAC in the Alq₃ layer.