Use of heteroaromatic spacers in isoindigo-benzothiadiazole polymers for ambipolar charge transport

Inspired by the outstanding charge-transport characteristics of poly(isoindigo-alt-benzothiadiazole) (PIIG-BT) in our previous study, herein we present two new polymers (PIIG-DTBT and PIIG-DSeBT) involving IIG and BT blocks constructed using five-membered heteroaromatic spacers such as thiophene (T) and selenophene (Se) and investigate the effects of the spacer groups on the optical, electrochemical, and charge-transport properties. As a consequence of the red-shifts induced by the more extended conjugation and enhanced intramolecular charge transfer (ICT), both PIIG-DTBT and PIIG-DSeBT show smaller bandgaps compared to PIIG-BT. Interestingly, the LUMO energy levels (-3.57 eV) for the two polymers are the same, but the HOMO levels (-5.39 and -5.26 eV for PIIG-DTBT and PIIG-DSeBT, respectively) clearly vary as a function of the structural modification of the spacers. In addition to the ch…