Synthesis of diketopyrrolopyrrole based conjugated polymers containing thieno[3,2-b]thiophene flanking groups for high performance thin film transistors

New donor-acceptor (D-A) conjugate polymers based on 3,6-bis(2-bromothieno-[3,2-b] thiophen-5-yl)2,5- bis(2-octyldodecyl) pyrrolo[3,4-c]-pyrrole-1,4-(2H, 5H)-dione (Br-TTDPP) combined with three different electron-donating monomers bithiophene (BT), di(2-thienyl) ethene (TVT), and di(selenophene2- yl) ethene (SVS) were synthesized. The optical band gap, electrochemical properties and organic fieldeffect transistor (OFET) device performance of the TTDPP-based polymers were systematically investigated. X-ray diffraction (XRD) was used to evaluate the molecular packing of the TTDPP-based polymers. Among three polymers, TTDPP-SVS showed the smallest d-spacing and the largest distance of 0.372 for pi-pi stacking. In particular, an OTFT having a TTDPP-SVS active layer showed the highest hole mobility of 0.196 cm(2) V-1 s(-1), the lowest threshold voltage down to -3.6 V, and the highest Ion/Ioff ratio of 6.5 x 10(4). This indicates that p-extended SVS significantly improves charge transport properties.