Shizuo Tokito

Polyarylenevinylene films prepared from precursor polymers soluble in organic solvents

Abstract Three polyarylenevinylenes, poly( p -phenylenevinylene), poly(2,5-dimethoxy- p -phenylenevinylene) and poly(2,5-thienylenevinylene), were prepared through new precursor polymers that were soluble in organic solvents. The new precursor polymers were chemically stable in air below 100°C. Thin precursor polymer films were obtained by spin coating from the organic solutions. Uniform, dense, and tough polyarylenevinylene films were obtained from the precursor polymer films by heat treatment in order to eliminate the pendant group. The optical and electrical properties of those polyarylenevinylenes were investigated. Oriented polyarylenevinylene films were obtained by stretching during thermal treatment.

Preparation of highly oriented polyarylenevinylene thin films by the Langmuir-Blodgett technique

We obtained three kinds of polyarylenevinylene(poly (p-phenylenevinylene), poly(2,5-dimethoxy-p-phenylenevinylene) and poly(2,5-thienylenevinylene)) thin films with the Langmuir-Blodgett (LB) technique. Stable polyarylenevinylene precursor-anionic amphiphile complex monolayers were formed at the air-precursor aqueous solution interface through adsorption of the precursors onto an amphiphilic monolayer. The polyion complex monolayers could be transferred on substrates by the LB technique. The polyarylenevinylene precursor LB films were converted to polyarylenevinylene films with a heat treatment under nitrogen flow. Extension of the mean n conjugation length and planar orientation of the conjugation sequences were realized in the poly (p-phenylenevinylene) and poly(2,5dimethoxy-p-phenylenevinylene) LB films.

Optical third-harmonic generation from poly(2,5-thienylene vinylene) thin films

Third‐harmonic generation measurements have been made on poly(2,5‐thienylene vinylene) (PTV) thin films. The third‐order optical susceptibility χ(3) was evaluated to be 3.2×10−11 esu at 1.85 μm wavelength. It was also revealed that in weakly iodine‐doped PTV thin films, χ(3) was almost the same value as that of nondoped films. χ(3) at a shorter wavelength region was expected to be much higher than that obtained in this work due to the resonant effect.

Preparation of high-quality poly(2,5-thienylenevinylene) films

Abstract Preparation of high-quality poly(2,5-thienylenevinylene) (PTV) films via organic solvent-soluble precursor polymers was investigated. The polymerization conditions for the preparation of stable and processable PTV precursor polymers are described. Complete conversion from the precursor polymer to PTV was realized by use of an acid catalyst. The fully converted PTV had no chemical defect originating from sp3-hybridized carbon.

Optical third‐harmonic generation from poly‐(2,5‐dimethoxy p‐phenylene vinylene) thin film

Third‐harmonic generation has been measured in poly(2,5‐dimethoxy p‐phenylene vinylene) thin film. The third‐order optical susceptibility, χ(3), was evaluated to be 5.4×10−11 esu at 1.85 μm wavelength. This χ(3) value is about one order higher than that for poly(p‐phenylene vinylene) and almost the same value as for poly(n‐BCMU diacetylene) which possesses the highest χ(3) value among processible (solvent castable) polymeric materials.

PHOTOCONDUCTION OF POLY(P-PHENYLENEVINYLENE) FILMS.

Large photoconduction in PPV films prepared via sulfonium salt process was found. The photocurrent was proportional to 0.5–0.7th power of the intensity of incident light. This suggested that recombination of photo-generated carriers played an important role in the photoconduction in PPV films. Photocurrent spectrum showed a huge broad peakin a near infrared region at which optical absorption was very weak.

Highly oriented polyarylenevinylene thin films

Abstract Oriented thin films of poly(2,5-dimethoxy-p-phenylenevinylene) (MO-PPV) and poly(2,5-thienylenevinylene) (PTV) were prepared. Methoxy-pendant precursors of MO-PPV and PTV, which are soluble in organic solvents and stable at around room temperature, were prepared. The precursors were spin-coated on polymer substrates, and were allowed to convert partially under well-defined conversion conditions. Then, polymer substrates were stretched at around 100°C under the flow of dry HCl gas which acted as catalyst for full conversion of precursors. Highly oriented thin films with the thickness of about 0.1 μm were obtained. Optical absorption spectra of oriented films exhibited large anisotropy which proved the alignment of π-conjugated chains. Also the shifts of π−π ∗ peaks to longer wavelength evidenced the increase of average π-conjugated length in oriented chains.

Appearance of Metallic Reflectance due to Conversion from Precursor Polymer to Poly(2,5-thienylenevinylene)

The optical absorption and reflectance of poly(2,5-thienylenevinylene) and its precursor polymer thin films were measured. It was found that the optical properties drastically changed and metallic reflectance appeared during conversion from the precursor polymer to poly(2,5-thienylenevinylene).

Electroluminescence in Vacuum-Deposited Organic Thin Films

Electroluminescence in organic thin films, ideally suited for large-area display devices, has been investigated by many researchers. The fabrication of thin-film EL cells using organic materials that exhibited high-EL efficiency has not yet been successful. Recently, Tang and VanSlyke reported a two-layer organic EL device with superior EL characteristics. /1/ Most recently, we proposed a new organic EL device with a three-layer structure; hole transport layer/emitting layer/electron transport layer./2, 3/ The introduction of hole and electron transport layers made possible the enhancement of the efficiency of hole and electron injection. Moreover, it made the selection of emitter materials free from the intractable technical problems of the fabrication of thin film EL devices; a polycrystalline emitting layer was sandwiched between two pin-hole free homogeneous, amorphous carrier transport layers in the resulting three-layer cells.