Designer Conjugation-Break Spacer That Boosts Charge Transport in Semiconducting Terpolymers

Conjugated polymers (CPs) are pivotal for high-mobility applications, typically avoiding nonconjugated units due to their perceived negative impact on charge transport. Contrary to this belief, our study introduces a nonconjugated unit, DKPDO, which when employed as a conjugation-break spacer (CBS), significantly enhances charge transport. DKPDO was obtained as a center-modified isoindigo variant featuring strongly electron-withdrawing amide groups that diminish the electron density and foster multiple hydrogen-bonding interactions. This results in enhanced electron deficiency and reinforced coplanarity relative to isoindigo. DKPDO was incorporated into a polymer backbone, comprising isoindigo and bithiophene, to create a series of terpolymers with varied molar ratios, allowing systematic evaluation of their solubilities, interchain interactions, crystallinities, and energy levels. Notably, incorporating DKPDO into the terpolymers results in a universal improvement of hole mobilities and operational stabilities over the DKPDO-free counterpart. Remarkably, the terpolymer containing 2.5% DKPDO achieves a high hole mobility of 4.12 cm2 V–1 s–1, approximately 6-fold higher than that of the parent CP and among the highest for CPs based on center-inserted isoindigo units. The study not only, for the first time, realizes charge transport enhancement with CBS in polymer backbones but also sets a precedent for the strategic use of nonconjugated units in developing high-performing CPs.