Novel dendritic light-emitting materials containing polyhedral oligomeric silsesquioxanes core

Abstract

A new series of star-like light-emitting materials (POSS1, POSS2 and POSS3) were synthesized by hydrosilylation of the polyhedral oligomeric silsesquioxane with 4,4′-bis(4-(di-(4-methylphenyl)amino)styryl)-2-(hexan-1-yloxy)-5-(10-undecen-1-yloxy)benzene (C1), 4,4′-bis[(E)-2-( N-ethylcarbazoyl)ethenyl]-2-(hexan-1-yloxy)-5-(10-undecen-1-yloxy)benzene (C2), and Iridium(III) bis(2-phenylpyridine-C 2- N′) (13-teradecenyl acetonate) (C3), respectively. All synthesized materials are soluble in common organic solvents, such as chloroform, toluene and 1,2-dichloroethane, and exhibit good film-forming properties. Therefore, they can be used to fabricate devices by spin-coating. The aggregation of peripheral chromophores can be prevented by the rigid POSS core. A double-layer, light-emitting diode with the configuration of indium–tin oxide/poly(ethylene 3,4-dioxythiophene)/POSS1/Ca/Al was fabricated using POSS1 as the active layer. The device emitted green light with a maximum brightness of 115 cd/m 2 and a current yield of 0.07 cd/A. When the light-emitting layer is blended with 0.8% electron-transport material, 2-(4′- tert-butylphenyl)-5-(4′-diphenyl)-1,3,4-oxadiazole, the maximum brightness and current yield of the device can reach 1469 cd/m 2 and 0.8 cd/A, respectively. The performance of a POSS2 device with the same device structure can reach 1102 cd/m 2 and 0.88 cd/A. POSS3 is a kind of triplet material and blended with 4,4- N,N′-dicarbazole-biphenyl as host material, to fabricate the light-emitting device. The maximum brightness and current yield reach 1008 cd/m 2 and 1.04 cd/A, respectively. Blending with 1,3,5-tris(2- N-phenylbenzimi dazolyl)benzene as the hole-blocking material yields a maximum brightness and current yield of 1172 cd/m 2 and 3.99 cd/A.