π-Extended Isoindigo-Based Derivative: A Promising Electron-Deficient Building Block for Polymer Semiconductors.

The exploration of novel electron-deficient building blocks is a key task for developing high-performance polymer semiconductors in organic thin-film transistors. In view of the situation of the lack of strong electron-deficient building blocks, we designed two novel π-extended isoindigo-based electron-deficient building blocks, IVI and FIVI. Owing to the strong electron-deficient nature and the extended π-conjugated system of the two acceptor units, their copolymers, PIVI2T and PFIVI2T, containing 2,2'-bithiophene donor units, are endowed with deep-lying highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy levels and strong intermolecular interactions. In comparison to PIVI2T, the fluorinated PFIVI2T exhibits stronger intra- and intermolecular interactions, lower HOMO/LUMO energy levels up to -5.74/-4.17 eV, and more ordered molecular packing with a smaller π-π stacking distance of up to 3.53 Å, resulting in an excellent ambipolar transporting behavior and a promising application in logic circuits for PFIVI2T in ambient with hole and electron mobilities of up to 1.03 and 1.82 cm V s, respectively. The results reveal that FIVI is a promising and strong electron-deficient building unit to construct high-performance semiconducting polymers, which provides an insight into the structure-property relationships for the exploration and molecular engineering of excellent electron-deficient building blocks in the field of organic electronics.