Investigation of novel carbazole-functionalized coumarin derivatives as organic luminescent materials

Four new carbazole-based coumarin derivatives comprising a carbazole core and one or two coumarin chromophores, 7-(diethylamino)-3-(4-(9-(p-tolyl)-9H-carbazol-3-yl)phenyl)coumarin (Cz-Ph-C) and 3,3'-((9-(p-tolyl)-9H-carbazole-3,6-diyl)bis(4,4′-phenyl))bis(7- (diethylamino)coumarin) (Cz-2(Ph-C)), 7-(diethylamino)-3-(5-(9-(p-tolyl)-9H-carbazol-3- yl)thiophen-2-yl)coumarin (Cz-Th-C) and 3,3'-((9-(p-tolyl)-9H-carbazole-3,6-diyl)bis(thiophene- 5,2-diyl))bis(7-(diethylamino)coumarin) (Cz-2(Th-C)), were successfully synthesized as the emissive materials for organic light-emitting devices. The photophysical, electrochemical properties and thermal stabilities of the compounds were systematically investigated. The results showed that these coumarin-carbazole hybrids exhibited excellent thermal stabilities and high photoluminescence quantum efficiencies in dichloromethane solutions, and they emitted strong green emissions. The vacuum-processed doped devices with a configuration of ITO/TAPC (20 nm)/TBADN: Coumarin-carbazole hybrid (x wt%, 30 nm)/TPBi (50 nm)/Liq (2 nm)/Al (150 nm) was fabricated, in which the devices based on Cz-Ph-C exhibited the best electroluminescence performance with a maximum brightness of 12910 cd/m2 and a maximum luminous efficiencies of 7.39 cd/A and a maximum external quantum efficiency (EQE) of 3.36%.