Synthesis and Electroluminescent Properties of Copolymers Based on Fluorene and 2,5-Di(2-hexyloxyphenyl)thiazolothiazole

A novel series of soluble conjugated random copolymers were synthesized via the Suzuki coupling reaction of 9,9-dihexylfluorene (DHF) and 2,5-di(2-hexyloxyphenyl)thiazolothiazole (TZ), with the TZ composition varying from 5 to 50 mol % in the copolymers. All of the copolymers exhibited good thermal stability and excellent solubility in common organic solvents, such as chloroform, toluene, and tetrahydrofuran. The electrochemical and photophysical properties were characterized in detail. Under UV excitation, these copolymers emitted bright blue fluorescence at around 416−420 nm in CHCl 3 solution and 446−451 nm in thin film form. Light-emitting diodes fabricated with the copolymers emitted bright blue light with external quantum efficiencies of 0.06−0.44%. The electroluminescence (EL) efficiency of the copolymer with a TZ content of 50% was more than 3 times that of the fluorene homopolymer. Preliminary EL studies showed that these copolymers had good electron transport properties arising from the introduction of TZ units. These copolymers are thus efficient blue emissive materials for polymer light-emitting diodes (PLEDs).