Nearly 50-50 Face-on to Edge-on Crystallites in Regioisomeric Polymers Based on n-Type Thienylvinyl-1,1-dicyanomethylene-3-indanone for High Electron Mobility

Abstract

To better understand how backbone regioregularity at the molecular level influences the bulk properties of conjugated polymers, we investigated the optical and electrochemical properties, energetics, microstructure, and charge transport characteristics of newly synthesized regioisomeric polymers. These include a regiorandom polymer (PTIC) and two regioregular analogs (PTIC-gamma and PTIC-delta). All these polymers exhibit a broad infrared absorption band covering from 300 to 1000 nm, a narrow band gap of 1.25 eV, and a low-lying lowest unoccupied molecular orbital deeper than 3.88 eV. PTIC-gamma features weaker chain-to-chain packing owing to its U-shape backbone, whereas PTIC and PTIC-delta present strong aggregation with their wave-like backbone shapes. Initially, all pristine polymer films reveal a bimodal texture dominated by a preferential face-on orientation. Following thermal annealing, the crystallites reorient further into a nearly exclusive face-on packing for PTIC-gamma and PTIC-delta films, whereas PTIC films maintain a roughly 50-50 face-on to edge-on orientation ratio. As a result, the best electron mobility, reaching 1.43 x 10-1 cm2 V-1 s-1, is achieved from the annealed PTIC film owing to the construction of a continuous 3D charge-transport pathway.