Tuning Charge Transport Behavior of Isoindigo-Based Polymers from Balanced Ambipolar to n-Type Preferred via Hydrogen Bond Formation

Hydrogen bond, as a type of high-strength non-covalent interaction, is adopted in the construction of highly planar polymer frameworks. In this context, a new type of conjugated polymer, P(5MeOII-Pyr) is synthesized by copolymerizing 5,5′-dimethoxy isoindigo (5MeOII) with pyrazine (Pyr). By demethylation, P(5OHII-Pyr) is obtained, in which the hydrogen bond between the hydroxyl group on the isoindigo core and the nitrogen atom on the pyrazine core is formed. Compared to P(5MeOII-Pyr), P(5OHII-Pyr) exhibits a red shift of ∼20 nm in UV-vis absorption, which is related to the planarization of the polymeric backbone due to the hydrogen bond formation. Both materials demonstrate high thermal stability, with thermal decomposition temperatures around 400 °C. Organic field-effect transistor devices (OFETs) with a top-gate bottom-contact configuration are fabricated using these two materials and their charge transport behaviors are compared. Notably, the electron mobility of P(5OHII-Pyr) increases more than tenfold compared to P(5MeOII-Pyr), while its hole mobility is greatly suppressed, making it a n-type-transport preferred material. This improvement is primarily due to the introduction of hydroxyl groups, which makes the polymer more planar, allowing better delocalization of LUMO, thereby facilitating electron transport along the polymer backbone.