H. Fujimoto

OPTICAL STUDIES ON THE MECHANISM OF ELECTRICAL CONDUCTION OF DOPED POLYACETYLENE.

Abstract Optical spectra are measured with the AsF5 and Br2 doped polyacetylene films. By the doping, the π → π band located in the 19000 cm−1region is disappeared, while the new bands are observed at 870, 1370 and 5000 cm−1 regions. In addition, other new absorption bands are found around 570 − 660 cm−1 region by decreasing the temperature of the doped thin films, which may be assigned to the transitions between the levels of the electron-hole pair. The reflection spectrum of the AsF5 doped film shows a metallic behavior and it is analysed assuming a presence of free carrier. The conductivity estimated by the optical data is in good agreement with the measured one. The reflectivity of the bromine doped film is less metallic presumably because the chemical reaction may take place. The logarithm of the conductivity shows T−1/4 dependence, indicating that the conductivity is dominated by the hopping of the carrier between the chains.

Optical constants of polyacetylene

Abstract Optical constants of neat cis - and trans -(CH) x and (CD) x films are determined by measuring infrared, visible and ultraviolet spectra of the film and its thickness directly. The absorption coefficient of cis -(CH) x at the absorption maximum 18 500 cm −1 was (1.5 ± 0.1) × 10 5 cm −1 and that of trans -(CH) x at 15 500 cm −1 was 1.5 × 10 5 cm −1 . The same values as those of (CH) x were obtained for (CD) x . The refractive indices and dielectric constants of cis - and trans -(CH) x were calculated based on absorptionvspectral data.

Quantitative optical study of I2-doped polyacetylene

Abstract The relation between dopant concentration and adsorption spectra of iodine-doped polyacetylene films is studied quantitatively with films whose iodine contents are analysed by radioactivation analysis. It is shown that the dopant content of thin polyacetylene film can be estimated from the absorption spectra. For heavily iodine-doped film, optical constants are determined from measured infrared, visible and ultraviolet spectra by the aid of the Kramers–Kronig relation. The absorption coefficient of 64% iodine-doped film at the absorption maximum of the mid-gap band, 7500 cm −1 , is 2.5 × 10 5 cm −1 and that of the same film at the adsorption maximum of the pentaiodide ion, 19 000 cm −1 , is 2.9 × 10 5 cm −1 , whereas the maximum value for undoped film at 18 500 cm −1 is 1.5 × 10 5 cm −1 ( cis -rich form).

Spectral Studies on the Charged Soliton of Polyacetylene

Abstract The optical spectra of polyacetylene doped with iodine (p type) or sodium (n type) are investigated in the infrared and visible region. The change of spectra with doping is measured quantitatively. Model structures of the charged soliton lattice are suggested for p and n type chains of the highest doping levels. The reflection spectra of (CHIy)x and (CDIy)x for heavy doped films are measured and analyzed by five transitions existing in 0 - 24000 cm−1 region. By lowering the temperature to 30 K, the gapless transition is disappeared presumably because the lattice with the charged soliton is frozen.

Nanosecond time-resolved photoinduced absorption of trans-polyacetylene

Abstract The photoinduced absorption and bleaching of trans -polyacetylene were investigated in nanosecond time regime for the first time. The transient absorption near the band gap and the bleaching of the interband transition were observed for both trans -(CH)x and trans -(CD)x. The absorption near the band gap saturates at ΔA/AO ∼ 0.01. The decay curves of transient absorbance change can be fitted to erf [( t /τ) − 1 2 ] . The time constants are 144±15 ns ((CH)x) and 305±27 ns ((CD)x) at 4 K and 32±6 ns ((CH)x) and 40±6 ns ((CD)x) at 290 K. When the trans content in cis -rich film decreases, the time constant becomes longer. The decay kinetics was interpreted by the interchain recombination of photoexcited polaron pairs.

Frequency and temperature dependences of 1H NMR T1 in pure and doped polyacetylene

Abstract Spin-lattice relaxation rates 1/T1 of 1H nuclei were measured in pure and Br2-doped trans-polyacetylene. At room temperature the frequency dependence obeyed 1/2 power law both in pure and doped. The temperature variation depended on samples in pure case. For first group samples the data points fitted a T1 vs T−1/4 law between 1.3 and 295 K at 9.0 MHz. At higher frequencies they deviated at low temperatures. For second group the temperature dependence was a little steeper. The T−1/4 law was explained by the phonon scattering of one-dimensionally moving electron spins (neutral solitons). In Br2-doped one a T1T=const. law fitted between 4.2 and 295 K.

Amplitude Modes in Mixed Polymers Trans [C2H2)y(C2D2) 1-y]x

Abstract Resonant Raman Scattering and doping induced IR absorption are explained in terms of amplitude modes of the 1-d gap. The RRS frequencies and relative intensities of the renormalized phonon lines at the various concentrations are readily obtained.

NMR, ESR and magnetic studies on (CH)x

Abstract A simple consideration of acoustic-phonon scattering gave D‖=D 0 T − 1 2 , as the diffusion constant of spin (neutral) solitons. T 1 ∝T − 1 4 , which was deduced from the temperature dependence of D‖, was found in the experimental data on 1H and 13C NMR in pristine trans-(CH)x.