Novel conjugated polymers based on bis-dithieno[3,2-: B;2′,3′- d] pyrrole vinylene donor and diketopyrrolopyrrole acceptor: Side chain engineering in organic field effect transistors

Two new donor-acceptor conjugated polymers, i.e. PB(C₁₂DTP)V-DTDPP-C₁₂ and PB(C₁₂DTP)V-DTDPP-C₁₂C₈, were prepared by the Stille coupling of (E)-1,2-bis(4-dodecyl-6-(trimethylstannyl)-4H-dithieno[3,2-b:2′,3′-d]pyrrol-2-yl)ethene (Sn-B(C₁₂DTP)V) with 3,6-bis(5-bromothiophen-2-yl)-2,5-didodecylpyrrolo[3,4-c]pyrrole-1,4-dione (Br-DTDPP-C₁₂) and 3,6-bis(5-bromo-thiophen-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4-dione (Br-DTDPP-C₈C₁₂), respectively. The molecular weight and thermal properties of the obtained polymers were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and thermogravimetry (TG). Their optical and electrochemical properties were analyzed by UV-vis-NIR spectroscopy and cyclic voltammetry (CV). The morphological and molecular-packing features of the polymers were characterized by optical microscopy and atomic force microscopy (AFM), UV polarization spectroscopy and grazing incidence X-ray diffraction (GIXD) to determine the relationship between the structural morphology and the performance. PB(C₁₂DTP)V-DTDPP-C₁₂C₈ with branched C₁₂C₈ side chains on DPP units shows much higher hole mobility (1.2 cm² V^-1 s^-1) than 0.69 cm² V^-1 s^-1 of PB(C₁₂DTP)V-DTDPP-C₁₂.