Hal Bon Gu

Absorption and Emission Spectral Changes in a Poly(3-Alkylthiophene) Solution with Solvent and Temperature

A remarkable change of the absorption spectrum has been observed in poly(3-alkylthiophene) solutions with changing temperature, which is tentatively interpreted in terms of a conformation change of polymer chains such as a rod-coil transition due to the change of the entanglement of alkyl chains with temperature. The emission intensity has been found to decrease remarkably at low temperature due to this transition.

Properties of free standing and composite conducting heterocyclic polymer films prepared utilizing lewis acids as catalysts

Abstract Heterocyclic conducting polymer films such as polypyrrole, polythiophene can be obtained as films in free standing state, uniform composite films and heterogeneous films composed of these heterocyclic polymers and various insulating polymers by the chemical means using FeCl 3 , MoCl 5 , etc. as catalysts. The free standing films indicate similar characteristics with those obtained by the electrochemical method. In uniform composite films, the electrical conductivity is found to be a function of the amounts of contained heterocyclic polymer. In heterogeneous composite films, the electrical conductivity and dielectric constant depend strongly on the thicknesses of the conducting layer and the insulating layer.

Effect of Ammonium Gas on Electrical Property of Conducting Polymers

Contrary to polyacetylene and polythiophene, the electrical conductivities of poly(p-phenylene) and poly(p-phenylenevinylene) can be increased remarkably by ammonium doping. This can be explained in terms of n-type doping. Diethylamine and triethylamine have also been found to be effective concerning these conducting polymers. The application of this effect as a sensor of gas and odor is also proposed.

Optical properties of solution of polythiophene derivatives as functions of alkyl chain length, concentration and temperature

Optical transmission through the cell of solutions of polythiophene derivatives such as poly(3-octylthiophene), poly(3-dodecylthiophene) and poly(3-dococylthiophene) has been found to change drastically with temperature and concentration. This transmission change is also dependent on the alkyl chain length. The critical temperature Tc of the transition between two transmission states (opaque and transparent) increases with increase in both concentration and chain legth. This phenomenon has been conjectured to originate in the change of light scattering due to some conformational transition of polymers in the solvent. An application of this phenomenon has also been proposed.

Doping effect in solution of poly(3-alkylthiophene)

Poly(3-alkylthiophene) in solution can be doped just as in the case of polythiophene films, resulting in the suppression of the interband absorption and the appearance of absorption peaks in the infrared region originating in the transitions between polaron states and from the valence band to the low-lying polaron state. Enhancement of the spin density by doping in an ESR measurement was also observed, which supports the polaron formation but not bipolaron formation. From these results, it has been clearly demonstrated that even a single polymer chain has the characteristics of conducting polymers.

Effects of Ammonia Gas on Properties of Poly (p-phenylene vinylene)

Effects of ammonia gas on the electrical conductivity, photoluminescence, optical absorption and electron spin resonance of poly (p-phenylene vinylene) (PPV) have been studied. The electrical conductivity and luminescence intensity in PPV have been found to increase upon exposure to ammonia gas in contrast to the well-known compensation effect of ammonia gas on other conducting polymers. The results are discussed in comparison with the data of lightly doped samples with p-type dopant (ClO 4 - ) and n-type dopant (TBA + ).

Surface potential decay measurement in conducting polymers and its doping effect

Abstract Surface potential decay in TCNQ doped PPS, PT, PCPA and PPV etc. is studied by corona charging method. The decaying speed of surface potential in conducting polymers is much faster compared with the case of insulating polymers. The decay time of the surface potential in TCNQ doped PPS is dependent on TCNQ TCNQ concentration and it is also influenced by a double doping of I2 into TCNQ doped PPS. The mobility of a conducting polymers is evaluated to be 10−8 – 10−7 cm2/V·sec from analysis of the potential decay curve. The mobility of PPV increased by the heat-treatment.

Thermally-Stimulated Current Measurements and Localized States in Polychlorophenylacetylene

Thermally-stimulated currents (TSC) in conjugated conducting polymer (polychlorophenylacetylene, PCPA) and their doping effects were studied. The TSC spectra in undoped and I2 doped PCPA are very complicated. The TSC is enhanced upon increasing the I2 concentration and a main peak is observed at around 30~60°C. This peak was separated by the thermal-cleaning method. The trap depths evaluated from an Arrhenius plot (log i vs 1 / T) of the initial rising part of the separated peak were about 0.24 and 0.4 eV, respectively, regardless of the amount of dopant. It is considered that a localized center either comprises existing defects originally in the PCPA or defects produced by doping with I2.