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 π-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 × 10-5 and 1.50 × 10-4 cm2/Vs, 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. ©2008 The Society of Polymer Science.