Shu Hotta

Novel organosynthetic routes to polythiophene and its derivatives

Abstract Polythiophene and its 3-alkyl derivatives have been synthesized by novel organosynthetic techniques. The organochemical syntheses were carried out by dehydrohalogenation of 2-halogenothiophene (or its 3-alkyl derivatives) or by dehydrogenation of thiophene (or its 3-alkyl derivatives). Copolymers can also be obtained from a solution involving two (or more) kinds of thiophene monomer species. The resulting polythiophene and its derivatives have well-defined chemical and electronic structure and molecular weights as large as 2.5 × 10 5 . The poly(3-alkylthiophenes) with long alkyl side groups, typically poly(3-hexylthiophene), are readily soluble in common organic solvents and can subsequently be processed into uniform films from their solution. These solution-cast films, furthermore, can be easily stretched up to a stretching ratio of about five. The stretched films exhibit excellent conductivity (as high as 200 S/cm) after doping. The effect of the copolymerization between two thiophene monomers is also discussed.

Vibrational spectra of charged defects in a series of α,α′-dimethyl end-capped oligothiophenes induced by chemical doping with iodine

We present the results of a detailed study carried out on a few α,α′-dimethyl end-capped oligothiophenes which have been in situ doped with dry iodine vapors, at different concentrations. The doping process of these well sized oligomers (from dimer to hexamer) has been monitored by using Fourier transform infrared absorption and Fourier transform raman scattering spectroscopies. These data, when combined with the vibrational full assignment of the oligomers in the neutral state and the electronic absorption bands recorded for both neutral and doped compounds, provide a complete spectroscopic characterization of a full series of positive polaron-type model defects of doped polythiophene. We have also performed density functional theory quantum-chemical calculations in order to analyze the effects of ionization on the geometries and vibrational spectra of these systems.

Fourier transform infrared study of electrochemically prepared polythienylene films with varying doping levels

Abstract Fourier transform infrared (FTIR) spectra of electrochemically prepared polythienylene films doped with various dopant species at varying doping levels have been obtained. These doped polythienylene films exhibit four conspicuous absorption bands at 1330 - 1310, 1200, 1220 - 1080 and 1030 - 1020 cm−1 made IR active and/or given prominent intensity due to the doping, independent of the difference in dopant species and contents. On the other hand, the bands specific to each dopant species are distinctly observable for the heavily-doped polythienylene films. Some typical band profiles in accordance with varied doping levels will be presented.

Efficiency of the π conjugation in a novel family of α,α′-bisphenyl end-capped oligothiophenes by means of Raman spectroscopy

The degree of π conjugation in a novel series of molecular materials containing a central oligothiophene moiety of variable length, with its end α positions capped by phenyl groups (PnTP; n=1–4) is closely inspected by means of Fourier-transform infrared and Fourier-transform Raman spectroscopies in the neutral state as solids. Density functional theory quantum chemical calculations were performed for each co-oligomer, at the B3LYP/6-31G** level, to obtain the optimized molecular geometry and force field. The thermal stability of these oligothiophenes has been also investigated, at the molecular level, by recording infrared and Raman spectra at different temperatures between −170 °C and 160 °C.

13C NMR spectrum analysis of electrochemically prepared polythienylene films

The 13C NMR spectrum analysis of electrochemically prepared polythienylene films has been investigated. Both a film doped with ClO−4 ions (PT–ClO4) and an undoped film (PT0) through the electrochemical reduction of PT–ClO4 give only two sharp absorption bands. The spectra of PT–ClO4 and PT0 are remarkably similar to each other in shape. These results demonstrate that both polythienylene are well‐defined polymers with only two kinds of carbon atoms which are compatible with dominance of the α–α′ linkage. The upfield shift of the absorption band for PT0 compared with PT–ClO4 is consistent with the increase in electron density through the electrochemical reduction.

13C NMR and Fourier transform infrared study of electrochemically prepared polythienylene film

Abstract The 13 C NMR and Fourier transform infrared (FTIR) spectra of an electrochemically prepared polythienylene film have been obtained. The polythienylene film displays only two sharp absorption bands, at 124.8 and 136.5 ppm downfield from TMS (tetramethylsilane) in the 13 C NMR, these being attributable to the carbon atoms in the β-position and the α-position, respectively, relative to the sulfur atom of poly(2,5-thienylene). The polythienylene film also shows a sharp absorption band at 789 cm −1 in the IR, which is definitely ascribable to the C-H out-of-plane vibration of poly(2,5-thienylene). The polythienylene film will be shown to have a highly defined structure with a dominance of poly(2,5-thienylene).

A new class of charge-transfer complexes: preparation of oligothiophene-TCNQ salts

Preparation des composes de transfert de charge entre le TCNQ et le ter- et le quaterthiophene. Conductivite electrique des complexes faibles (10 −10 , 10 −9 S/cm)

Electrochemically prepared poly(3-methylthienylene) films doped with iodine

Abstract Electrochemically prepared poly(3-methylthienylene) films doped with iodine have been investigated and the relationship between their conductivity and iodine content was studied. The conductivity of the films with various iodine contents was obtained in accordance with an Arrhenius equation with an activation energy equal to 0.17 to 0.033 eV. The highest conductivity was 5 S cm−1. The activation energy, which is dependent on the iodine content, shows discontinuous change, as is the case with polyacetylene doped with iodine. The relationship between conductivity and structure of the poly(3-methylthienylene) films will be discussed.

Surface Potential Measurement of Oligothiophene Ultrathin Films by Kelvin Probe Force Microscopy.

Surface structures and local surface potential of oligothiophene single molecular films deposited on metal substrates were investigated by Kelvin probe force microscopy using the frequency modulation detection method. Two-dimensional growth of the dimethylquinquethiophene (DM5T) films with the molecular axes perpendicular to the metal substrates was observed. Furthermore, the obtained surface potential of the DM5T film was 170 mV higher than that of Pt substrate and 200 mV lower than that of Ta substrate.

13C NMR spectrum analysis of electrochemically prepared poly(3-methylthienylene) films

Abstract The 13 C NMR spectrum analysis of electrochemically prepared poly(3-methylthienylene) films has been investigated. Both a film doped with ClO 4 ions (P3MT-ClO 4 ) and an undoped film (P3MT 0 ) give only two distinct absorption bands through the electrochemical reduction of P3MT-ClO 4 . These distinct bands are definitely attributable to the methyl group (upper field) and the thiophene ring (lower field), respectively, and are characteristic of well-defined poly(3-methylthienylene). The correlation between conductivity and 13 C NMR spectra will be discussed.