S. D. D. V. Rughooputh

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.

Time-resolved excitonic luminescence processes in poly(phenylenevinylene)

Integrated luminescence spectra, time-resolved luminescence spectra, and luminescence decay times of stretch-oriented poly(phenylenevinylene) (PPV) are studied in the temperature range 300∼12 K. The reflectance spectrum at room temperature is also studied. The luminescence spectrum is composed of vibronic bands and a broad band, which are interpreted as caused by radiative annihilation of free and selftrapped excitons, respectively. Temperature dependence of the intensity of free-exciton luminescence and temperature dependence of the decay time are interpreted in terms of relaxation of excitons. The height of a potential barrier, which separates the free exciton state and the self-trapped state, is found to be 350 cm -1 . At 20 K, exciton relaxation toward the self-trapped state occurs by a quantum-mechanical tunneling process. The tunneling rate obtained is (90 ps) -1 .

Fluorescence studies of poly(3-hexylthiophene) solutions

Abstract We report luminescence studies of a non-degenerate ground-state, poly(3, n-hexylthiophene), in solution. Photoexcitation of the polymer in solution at room temperature results in luminescence decay that is relatively short-lived (∼600 ps). The fluorescence quantum yield decreases with decreasing temperature. From studies of the temperature-dependence of the emission profiles, we calculate the formation energy, which is associated with the observed fluorescence, of ∼1.4 KCal/mole.

X-ray scattering study of the conversion of poly(p-phenylene vinylene precursor to the conjugated polymer

Abstract We have studied the transition of the highly oriented precursor of poly(p-phenylene vinylene) [PPV] to the conjugated PPV by using X-ray scattering. The conversion was achieved by thermal treatment of oriented precursor polymer films. The data show an increase in the crystallinity with conversion. The evolution of the scattering linewidths suggests that the PPV crystal domains formed during conversion grow in size with further thermal treatment. While conversion reduces the interchain distances, the longitudinal unit cell length increases. At higher conversions, packing of the crystal domains seems to promote orientational ordering.

Recent progress in conducting polymers: Opportunities for science and opportunities for technology

Abstract The remarkable electrical and mechanical properties of conducting polymers formed the initial (and continuing) basis of interest in the field. Recent results have demonstrated progress in the development of conducting polymer blends as composite materials without a percolation threshold.

Poly(p-phenylene vinylene): Incipient doping in conducting polymers

Abstract High molecular weight organic solvent soluble precursor polymers poly (p-xylylene-α-dimethylsulfonium salts), 1 – 4 were prepared. Polymers were characterized by Infrared spectroscopy as well as by elemental analysis. A DSC scan of polymer 1 was similar to poly (p-xylylene-α-dimethylsulfonium chloride) and the sample after the scan was yellow-orange, typical of PPV. However, the DSC scan of polymers 2 – 4 showed multiple endo and exothermic peaks and samples after the scan were black and conducting. We interpret this result by introducing a new concept which we call Incipient Doping . IR spectra of the incipeintly doped film of polymer 4 showed reduced intensity of the peaks due to dimethyl sulfide group but peaks to AsF6- were very strong. Results of physical characterization (conductivity, etc) are discussed.

Implications of the new high conductivity polyacetylene

Abstract With the development of a technique [1] for synthesizing polyacetylene with reduced sp 3 defect content, new insights into the distinction between the intrinsic and morphological properties of fibrillar (CH) x , and into the nature of the instrinsic material have become possible. In this paper we summarize the results of transport measurements on the Naarmann/Theophilou material. These results are compared with those from the standard Shirakawa material. The doping regime in which the temperature dependence of the measured conductivity reflects intrinsic transport is distinguished from that in which the measurements are dominated by sample morphology. Finally, the problem of non-uniform doping is considered, and a projection is given for the conductivity under optimal doping conditions.

Exciton annhihilation dynamics in poly(phenylenevinylene)

Luminescence processes of stretch-oriented poly(phenylenevinylene) (PPV) are investigated from a view point of exciton dynamics. It is found that PPV belongs to the category of strong exciton-phonon coupled system and provides a unique example where transient free-exciton luminescence is observable in time-integrated spectra at room temperature. It is also found that the height of the self-trapping barrier is 350 cm −1 , and the exciton tunneling rate is (90 ps) −1 . The small luminescence quantum efficiency (∼0.1 %) is explained as a result of a large lattice relaxation