Syntheses, properties, and field-effect transistors of small band gap quinoxaline- and thienopyrazine-vinylene/ethynylene conjugated polymers

Abstract

New conjugated copolymers of quinoxaline (AQ) and thienopyrazine (ATP) with vinylene (V) or ethynylene (E), poly[2,3-bis(4-(2-ethylhexyloxy)phenyl)-quinoxaline vinylene] (PAQV), poly[2,3-bis(4-(2-ethylhexyloxy)phenyl)-quinoxaline ethynylene)] (PAQE), poly[2,3-bis(4-(2-ethylhexyloxy)phenyl)-thieno[3,4-b]pyrazine vinylene] (PATPV), and poly[2,3-bis(4-(2-ethylhexyloxy)phenyl)-thieno[3,4-b]pyrazine ethynylene] (PATPE), were successfully synthesized by Stille coupling reaction. The optical band gaps of the PAQV, PAQE, PATPV, and PATPE were 1.86, 2.00, 0.88, and 0.90 eV, respectively, whereas the electrochemical band gaps were 1.99, 2.06, 1.00, and 1.06 eV, respectively. The reduced steric hindrance by the incorporation of the V or E linkage or the intramolecular charge transfer between the acceptor and the V or E linkage led to the small band gap. The AQ/ATP-vinylene copolymers exhibited much higher vis/near infrared absorption intensity than the AQ/ATP-ethynylene suggested the stronger π–π* transition intensity in the former and led to better charge-transporting characteristics. The saturation field-effect hole mobilities of the PATPV were 2.1 × 10−3, 1.7 × 10−2, and 1.1 × 10−2 cm2 V−1 s−1 on bare, octyltrichlorosilane (OTS)-treated, and octadecyltrichlorosilane(ODTS)-treated SiO2, respectively, with on-off current ratios of 35, 6.02 × 102, and 7.56 × 102. On the other hand, the estimated field-effect transistor hole mobility of the PATPE was in the range of 1.7 × 10−6–8.1 × 10−4 cm2 V−1 s−1, which was significantly smaller than those of the PATPV. The small band gaps and high charge carrier mobility of the prepared copolymers suggested their potential applications for near-infrared electronic and optoelectronic devices. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 74–81, 2010