S. Hotta

Structural and absorption studies of the thermochromic transition in poly(3-hexylthiophene)

Abstract We present initial data from x-ray diffraction, ultraviolet-visible (UV-VIS) absorption, and infrared (IR) absorption spectroscopy measurements made during thermal cycling of unoriented, solution cast, poly(3-hexylthiophene) films. The x-ray studies clearly indicate that a bulk structural order-disorder transition occurs concurrently with the known thermochromic transition. In particular, we characterize and describe the physical changes which occur during this very broad, and somewhat unusual, transformation at temperatures from 100°C to 180°C. From the x-ray data it appears that this transition is completely reversible. However, the transition exhibits marked thermal hysteresis. In addition, careful analysis of the UV-VIS and IR absorption data clearly identify irreversible processes. The significance of these results, with reference to the specific electronic properties of the polymer backbone, will be discussed.

Conducting polymer composites of soluble polythiophenes in polystyrene

Abstract We report optical and electronic properties of composites of soluble polythiophene derivatives and polystyrene over the full range of composition. The composite films were prepared by evaporating the solvent in an inert atmosphere from a solution containing both polymers. The films, made conducting by charge transfer doping (reaction with NOPF6 in acetonitrile), display an insulator-metal transition at the percolation threshold: a volume fraction of ≈16% conducting polymer in polystyrene.

Electrochemical synthesis and spectroscopic study of poly(3-alkylthienylenes)

Abstract The class of poly(3-alkylthienylenes) [P3ATs] has been synthesized by an improved method of electrochemical polymerization carried out under a rigorously oxygen-free and moisture-free environment. Within this class, the highest conductivity (750 S/cm) was obtained for poly(3-methylthienylene). The P3ATs (carrying hydrocarbon chains with carbon numbers of four or more) also show relatively high conductivities ranging from about 1 to 10 2 S/cm. The P3ATs with relatively longer hydrocarbon chains show good solubility in various organic solvents and can be readily processed from solution both in the neutral and in the conducting (oxidized) form. Copolymers based on the soluble P3ATs (obtained from random copolymerization of two kinds of thiophene monomers) are characterized by their high conductivity and excellent solubility. The influence of the hydrocarbon side chains on the electronic structure of the π-conjugated system of P3ATs is discussed.

Charge storage on a conducting polymer in solution

Abstract Magnetic and optical studies of poly(3-hexylthienylene) doped in solution with NO+PF6− in both choloroform and in the more polar solvent methylene chloride indicate a relatively small difference in the energy of polarons versus biplarons, and imply that the weak effective electron-electron Coulomb repulsion can be controlled by varying the solvent and/or the polymer concentration. Even though bipolarons are found to have a lower creation energy than a pair of polarons, entropy favors polarons at dilute concentrations. As a result, we have observed unambiguous magnetic and optical signatures characteristic of polarons in P3HT in CH2Cl2 at the lowest doping levels. The relative fraction of polarons and bipolarons has been analyzed in the context of various proposed statistical models. A theoretical model is developed to include the effect (in such solutions) of ionic screening on the effective Coulomb interaction. This model is tested by adding salt to a dilute solution of doped polymer.