Decked-out thiophene adds versatility to semiconducting polymers

Semiconducting polymers used for making light-emitting diodes, solar cells, and transistors have come a long way since the materials were first commercially developed in the 1980s. One of the important advances has been taking the original monomers such as thiophene and designing derivatives that allow researchers to better control polymer electronic properties, thus leading to improved device performance. In the latest example, Itaru Osaka of RIKEN’s Center for Emergent Matter Science and coworkers have created an imide-functionalized tetrathiophene as a new electron-deficient semiconducting polymer building block (Adv. Mater. 2016, DOI: 10.1002/adma.201601373). The researchers drew inspiration from bithiopheneimide, a molecule already known for its electron-withdrawing imide group’s knack for enhancing polymer electron-acceptor abilities. To enhance those abilities further, the team used a multistep reaction to synthesize a fused dimer of the compound functionalized with branched N-alkyl groups. The researchers then used the dimer, called dithienylthieno­thiophenebisimide, or TBI, together with thiophene- or thiazole-based monomers to make a series of copolymers. Osaka and coworkers found that the copolymers can function as p-type or n-type semiconductors in photovoltaic and transistor devices, depending on the molecular structure. They believe TBI may be the most versatile semiconducting polymer building block now available.