Synthesis of new fluorene-indolocarbazole alternating copolymers for light-emitting diodes and field effect transistors

New alternating copolymers of poly(2,7-(9,9'-dihexylfluorene)-alt-3,9-(5,11-di(2-ethylhexyl)-indolo[3,2-b]carbazole)) (PF-p-In) and poly(2,7-(9,9'-dihexylfluorene)-alt-2,8-(5,11-di(2-ethylhexyl)-indolo[3,2-b]carbazole)) (PF-m-In) were synthesized by palladium-catalyzed Suzuki coupling polymerization and characterized for the applications of light-emitting diodes and field effect transistors (FET). The incorporation of indolocarbazole into polyfluorene could not only enhance hole transporting properties but also thermal properties. The para-linkage, PF-p-In, facilitates pi-electron delocalization and thus has a lower optical band gap and a higher emission maximum than those of the meta linkage, PF-m-In. The electroluminescence devices based on PF-p-In and PF-m-In as the emissive layer show a similar maximum luminance but with different emissive colors of green and blue, respectively. The FET hole mobilities of PF-p-In and PF-m-In are 6.73 x 10(-5) and 1.50 x 10(-4) cm(2) /V center dot s, respectively, which are significantly higher than that of polyfluorene. The present study demonstrates the electronic and optoelectronic properties of polyfluorene enhanced by incorporating hole transporting indolocarbazole with different linkages.