Synthesis and Optoelectronic Characterizations of Conjugated Polymers Based on Diketopyrrolopyrrole and 2,2′-(thieno[3,2-b]thiophene-2,5-diyl)diacetonitrile Via Knoevenagel Condensation

Conjugated polymers have attracted extensive attention as semiconducting materials in wearable and flexible electronics. In this study, we utilize atom-economical Knoevenagel reaction to construct two conjugated polymers, PTDPP-CNTT and PFDPP-CNTT, based on dialdehyde-thiophene/furan-flanked diketopyrrolopyrrole (DPP) and 2,2′-(thieno[3,2-b]thiophene-2,5-diyl)diacetonitrile (CNTT). The resulting polymers exhibited suitable highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) energy levels, small bandgaps, and broad UV–vis–NIR absorptions (≈400–1000 nm), endowing them with photothermal and balanced ambipolar semiconducting properties with hole and electron mobilities over 10⁻³ cm²V⁻¹s⁻¹. Additionally, PTDPP-CNTT-based organic field-effect transistors (OFETs) devices show photo-responsive characteristics at 808 and 980 nm in the hole transport channel with the photo-responsivenesses of 9.0 × 10⁻³ A/W and 0.4 A/W, respectively, suggesting potential application in organic NIR-phototransistors.