Thiophene‐ S , S ‐dioxidized Indophenine: A Quinoid‐Type Building Block with High Electron Affinity for Constructing n‐Type Polymer Semiconductors with Narrow Band Gaps

Three thiophene‐ S , S ‐dioxidized indophenine (IDTO) isomers, 3 a ( E , E , E ), 3 b ( Z , E , E ), and 3 c ( Z , E , Z ), were synthesized by oxidation of an indophenine compound. 3 b and 3 c could be converted into the most‐stable 3 a by heating at 110 °C. An IDTO‐containing conjugated polymer, PIDTOTT, was prepared using 3 a as a comonomer through a Stille coupling reaction, and it possesses a narrow band gap and low energy levels. In organic field effect transistors (OFETs), PIDTOTT exhibited unipolar n‐type semiconductor characteristics with unexpectedly high electron mobility (up to 0.14 cm 2  V −1  s −1 ), despite its rather disordered chain packing.