Synthesis of a Novel Family of Polysilsesquioxanes Having Oligothiophenes with Well-Defined Structures

Our recent results on the synthesis and properties of a novel family of polysilsesquioxanes having oligothiophenes were reviewed. The polymers anchored on SiO2 or ITO substrates showed excellent mechanical hardness due to the formation of a three-dimensional siloxane network structure and chemical linkage between polymer and the surface of metal-oxide substrates. Optical, electrochemical, and electrical properties of polymers were also investigated

Optical absorption spectrum of pentacene cation radicals measured by charge-modulation spectroscopy

Charge-modulation spectroscopy was applied to vacuum-sublimed films of pentacene in the metal-insulator-semiconductor configuration with Parylene-C or cross-linked polymer as insulator. The spectrum exhibited several peaks in the wavelength range of 300-800 nm. The signal in the visible was ascribed to the field-modulation effect of a neutral pentacene film, while the three broad peaks in the UV exhibited field and frequency dependences different from those in the visible and were ascribed to the optical absorption due to a monocation radical of pentacene. This assignment was supported by the calculation reported earlier on the basis of the time-dependent density functional theory

Interference and electro-optical Kerr effects responsible for electroabsorption spectra of transparent Parylene-C films

Electroabsorption spectra of Parylene-C films are found to exhibit several peaks whose wavelengths depend on the thickness of the film. The spectral feature is well correlated to the first derivative of the transmission spectrum of the Parylene-C film sandwiched between two reflective metal layers, and the peak intensities are in proportion to the square of the magnitude of a modulation voltage. The electroabsorption spectra observed in a transparent region of the electrically insulating films are accounted for in terms of the interference effect coupled with the electro-optical Kerr effect of the Parylene-C films

Development of a simple method for fabrication of transparent conductive films with high mechanical strength

We have developed a simple method of fabricating transparent conductive films with a high mechanical strength on glass and indium tin oxide substrates. It does not require a large excess of organic solvents and polymerization catalysts and can yield smooth films by spin-coating of a mixture of a commercially available aqueous dispersion of poly(3,4-ethylenedioxythiophene)-poly(4-styrene sulfonate) and a neat liquid of tetraethyl orthosilicate. Preparation conditions such as feed ratio, kinds of additives, and annealing temperature and time were optimized to give highly conductive, transparent and mechanically strong films

Electrical Characteristics of Pentacene Films on Cross-Linked Polymeric Insulators of Varying Thicknesses

Pentacene films vacuum-sublimed on a cross-linked polymeric insulator (CPVP–C₆) prepared using poly­(4-vinylphenol) (PVP) and 1,6-bis­(trichlorosilyl)­hexane (C₆) were studied with a special concern on possible influences of the CPVP–C₆ thickness on the electrical characteristics of the pentacene films. It was found that the conductivities of the pentacene films on a thin CPVP–C₆ film (10 nm) were approximately 2 orders of magnitude higher than those on a glass substrate and increased slightly with the increase in the thickness of the underlying CPVP–C₆ film. In addition, the X-ray diffraction measurements showed that the stacking structure of pentacene molecules was remarkably enhanced by increasing the thickness of the CPVP–C₆ film, suggesting that the increase in conductivity is due, at least in part, to the improvement in carrier mobilities caused by the growth of large pentacene grains. An attempt to directly evaluate carrier mobilities using pentacene/CPVP–C₆ field-effect transistors was made, and a seeming increase in the carrier mobilities observed with the increase in the CPVP–C₆ thickness was ascribed to a hygroscopic nature of the CPVP–C₆ film, which was evidenced by the capacitance and quartz crystal microbalance measurements. Possible reasons are discussed to explain the enhanced conductivities of the pentacene films on the increased thicknesses of CPVP–C₆

Development of anchored oligothiophenes on substrates for the application to the tunable transparent conductive films

Bis(triethoxysilyl)-substituted oligothiophene with a moderate π-conjugation length was newly synthesized and polymerized to give a polysilsesquioxane network having oligothiophene units dispersed homogeneously without phase separation. The polymer was fixed on glass or ITO substrate by spin-coating and annealing. The resulting film exhibited a high mechanical strength due to the covalent bonding with the substrates, and was electrochemically stable even after 300 redox cycles in electrolyte solution. Chemical oxidation of the polymer films yielded electrically conductive and almost transparent films