Regioisomeric Cyanated Polythiophenes Bearing Polar Side Chains for n-Type Organic Thermoelectrics

The development of n-type polymers with high thermoelectric performance remains a major challenge for organic thermoelectrics. Herein, by devising two new isomeric cyano-functionalized bithiophene building blocks bearing polar side chains, we report two novel donor-acceptor-configurated n-type polythiophene polymers (BTOgCN-FT and BTCNOg-FT) with regiochemically tuned intramolecular S···O noncovalent interactions (INIs) and cyanation patterns for n-type thermoelectric application. The results show that cyanation furnished low-lying LUMO energy levels approaching that of the benchmark n-type polymer N2200 for both polymers (∼−3.90 eV), which combine with their polar side chain-enabled high dopant miscibility, leading to efficient n-doping efficiencies. Detailed theoretical and experimental studies also suggest that BTOgCN-FT exhibited a more planar backbone conformation and more ordered interchain packing in film state, thus yielding higher electrical values than BTCNOg-FT. Therefore, the polymer BTOgCN-FT eventually displays an optimal power factor (PF) value of 2.77 μW m^-1 K^-2, which is higher than that of BTCNOg-FT (1.50 μW m^-1 K^-2) and also largely outperforming that of the thoroughly investigated and optimized polymer N2200 (typical PF value of 10^-2 μW m^-1 K^-2). Our work not only presents two novel structurally simple and isomeric electron-accepting building blocks but also offers valuable structure-property correlations for the future design of high-performance n-type thermoelectric materials.