Solvent based hydrogen bonding: impact on poly(3-hexylthiophene) nanoscale morphology and charge transport characteristics.

We demonstrate that supramolecular assembly and subsequent enhancement of charge transport characteristics of conjugated polymers can be facilitated simply by adding small amounts of a more volatile poor solvent, which can hydrogen bond with the majority solvent. Addition of up to 2 vol % acetone to a precursor solution of poly(3-hexylthiophene) (P3HT) in chloroform leads to approximately a 4-fold increase in P3HT field-effect mobility. The improvement is associated with hydrogen bonding interactions between acetone and chloroform which decrease the evaporation rate of the mixed solvent. P3HT is less soluble in the binary solvent than in the more readily vaporized chloroform component, and this characteristic enables the supramolecular assembly of P3HT chains at the nanoscale. Two-dimensional molecular ordering of the polymer film was controlled by varying the quantity of poor solvent added to the precursor solution, and the correlation between field-effect mobility and molecular ordering was investigated. Hansen solubility parameters were used to systematically understand how the solvent mixture enhances the alignment and assembly of polymer chains and influences subsequent thin film properties. The value of the relative energy difference (RED) of the solvent with respect to P3HT increased from less than 1 to more than 1 during film formation, which indicates that the solvent characteristics are initially those of a good solvent but transform into those of a poor dissolution medium. A mechanistic illustration of the molecular ordering process during film formation is postulated.

3-Benzyl-5-phenyl-2-p-tolylthiophene.

The crystal structure of 3-benzyl-5-phenyl-2-p-tolylthiophene, C24H20S, is described. The thiophene ring in the title compound is planar and its structural properties are very similar to those of thiophene. The thiophene ring in compound (1) is planar as are the phenyl rings. The structure of the thiophene ring in compound (1) is very similar to that of thiophene (Bak, Christensen, Hansen-Nygaard & Rastrup-Andersen, 1961; Bak, Christensen, Rastrup-Andersen & Tannenbaum, 1956; Harshbarger & Bauer, 1970). The C-S distances are 1.735 (2) and 1.731 (2) A, respectively, and the C-S-C bond angle is 92.3 (1) degree. The steric repulsion between the p-tolyl ring at C(2) and the benzyl group at the adjacent carbon, C(3), is minimized by the rotation of the p-tolyl group 56.1 degrees from the thiophene plane. The benzene ring at C(5) deviates from the plane of the thiophene ring by 36.9 degrees. In 2,5-bis(4-nitro-phenyl)-3,4-diphenylthiophene (Meester, Maldar, Hosmane & Chu, 1986) the angle between the 4-H nitrophenyl and thiophene rings is 26.6 degrees. The angle between the phenyl and thiophene rings in 2-amino-4-methyl-5-phenylthiophene-3-carboxamide is 54.9 degrees (Joseph, Selladurai, Kannan & Parthasarathi, 1991).