Novel aminoalkyl-functionalized blue-, green- and red-emitting polyfluorenes

A family of aminoalkyl functionalized blue-, green- and red-emitting polyfluorene based copolymers were synthesized by Suzuki copolymerization. Dibenzothiophene-S, S-dioxide-3,7-diyl (FSO), 2,1,3-benzothiadiazole (BT) and 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DTBT) were incorporated into the backbone of copolymers as blue, green and red chromophores, respectively. It was realized that for all these aminoalkyl functionalized copolymers, the thermal stabilities, UV-vis absorption and electrochemical properties are not affected by molar ratio of aminoalkyl side groups. However, the increased amino-groups content can induce the formation of excimer in FSO based blue-emitting copolymer, which in turn leaded to broadened photoluminescence and electroluminescence spectra along with decreased emission efficiency. In contrast, device based on green and red-emitting copolymers exhibited stable emission, and device performance improved progressively with the enhanced content of aminoalkyl co-monomers. Comparing to the copolymers without aminoalkyl side chains, aminoalkyl functioned materials exhibited distinctly improved device performances for the application as emissive layer in light emitting diodes using high work-function Al as cathode due to the formation of interfacial dipoles that can facilitate electron injection. The maximum luminous efficiency of 3.28, 7.31 and 0.79 cd A (1) was achieved based on copolymers BFN1, GFN15 and RFN15, respectively with device architecture of ITO/PEDOT:PSS/PVK/copolymer/Al. These results indicate that aminoalkyl functionalized copolymers can have great potential for the application as efficient light-emitting layer with high work-function/air-stable cathode. (C) 2014 Elsevier B.V. All rights reserved.