Synthesis, properties, and field effect transistor characteristics of new thiophene-[1,2,5]thiadiazolo[3,4-g] quinoxaline-thiophene-based conjugated polymers

Four new conjugated copolymers based on the moiety of bis(4-hexylthiophen-2-yl)-6,7-diheptyl-[1,2,5]thiadiazolo[3,4-g]quinoxaline (BTHTQ) were synthesized and characterized, including poly(6,7-diheptyl-4,9-bis(4-hexylthiophen-2-yl)[1,2,5]thiadiazolo[3,4-g]quinoxaline) (PBTHTQ), poly-(6,7-diheptyl-4,9-bis(4-hexylthiophen-2-yl)-[1,2,5]thiadiazolo-[3,4-g]quinoxaline-alt-2,5-thiophene) (PTTHTQ), poly(6, 7-diheptyl-4,9-bis(4-hexylthiophen-2-yl) [1,2,5]-thiadiazolo-[3,4-g]quilloxaline-alt-9,9dioctyl-2,7-fluore-ne) (PFBTHTQ), and poly(6,7-diheptyl-4,9-bis(4-hexylthiophen-2-yl)11,2,5]thiadiazolo[3,4-g]quinoxaline-alt-1,4-bis(decyloxy)phenylene) (PPBTHTQ). The of PBTHTQ, PTTHTQ, PFBTHTQ, and PPBTHTP thin films was shown at 780, 876, 734, and 710 nm, respectively, with the corresponding optical band gaps (E-g(opt)) of 1.31, 1.05, 1.40, and 1.43 eV The relatively small band gaps of the synthesized polymers suggested the significance of intramolecular charge transfer between the donor and TQ moiety. The estimated hole mobilities of PBTHTQ, PTTHTQ, and PFBTHTQ-based field effect transistor devices using CHCl3 solvent were 8.5 x 10(-5), 8.5 x 10(-4), and 2.8 x 10(-5) cm(2) V-1 s(-1), respectively, but significantly enhanced to 1.6 x 10(-4), 3.8 x 10(-3), and 1.5 x 10(-4) cm(2) V-1 S-1 using high boiling point solvent of chlorobenzene (CB). The higher hole mobility of PTTHTQ than the other two copolymers was attributed from its smaller band gap or ordered morphology [wormlike (chloroform) or needle-like (CB)]. The characteristics of small band gap and high mobility suggest the potential applications of the BTHTQ-based conjugated copolymers in electronic and optoelectronic devices. (C) 2008 Wiley Periodicals, Inc.