Enhancing n-type charge transport in organic transistors: Cyano-functionalized thienylene-vinylene-thienylene (TVT) polymers

The development of high-performance n-type polymer semiconductors for organic field-effect transistors (OFETs) relies critically on the rational design of electron-deficient conjugated building blocks. Although cyano (CN)-functionalized materials present strong electron-withdrawing capability, the introduction of bulky CN substituents often leads to steric hindrance, reducing backbone planarity and impairing intramolecular charge transport. In this study, a rational molecular design strategy to overcome these limitations by strategically incorporating CN groups into the vinylene segment of the planar thienylene-vinylene-thienylene (TVT) unit was investigated. Two monomers—M1 (mono-CN substituted) and M2 (di-CN substituted) were synthesized and subsequently polymerized with diketopyrrolopyrrole (DPP) acceptor via Stille coupling, yielding conjugated polymers P1 and P2, respectively. Density functional theory calculations confirm that the CN functionalization at the vinylene linkage maintains excellent backbone planarity, which significantly lowering the lowest unoccupied molecular orbital (LUMO) energy levels. Moreover, electrostatic potential (ESP) analysis reveals that the additional CN substituents in P2 promote a well-defined alternating donor-acceptor structure, notably enhancing intramolecular charge transfer compared to the mono-substituted analogue P1. The UV–vis spectroscopy, cyclic voltammetry (CV), and temperature-dependent optical studies, demonstrate that P2 exhibits stronger intermolecular aggregation, a more pronounced ICT effect, deeper LUMO levels, and more ordered molecular stacking in solid-state thin films. Organic transistor devices based on P2 achieve a high electron mobility of 1.03 cm² V⁻¹ s⁻¹ after thermal annealing, nearly twice that of P1 (0.52 cm² V⁻¹ s⁻¹). These results highlight the effectiveness of rational CN functionalization at the vinylene site within the TVT backbone, offering a promising strategy for developing high-performance n-type polymer semiconductors.