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 cm2 V−1 s−1), despite its rather disordered chain packing. Three isomers of thiophene‐S,S‐dioxidized indophenine (IDTO) were conveniently synthesized through oxidation of an indophenine compound. Two of the three isomers could be converted into the most stable isomer, (E,E,E)‐IDTO, by heating at 110 °C. The conjugated polymer PIDTOTT based on (E,E,E)‐IDTO displayed unipolar n‐type semiconductor characteristics with surprisingly high electron mobility (up to 0.14 cm2 V−1 s−1).