We measured small Faraday polarization rotation in nanopolyacetylene in a magnetic field approximately 150 Oe. We found that approximately 1% polyacetylene nanoparticles increase up to 50% the polarization rotation angle of the transparent matrix containing them when probed near and at the NPA absorption band. The rotation angles were in the range 1 - 15 (mu) rad.
Dipole-forbidden states of trans-nanopolyacetylene in the near infra-red are probed by a photothermal method at room temperature. We found that light absorption at approximately 1 micrometers is four orders weaker than that corresponding to the main dipole-allowed transition.
It has been demonstrated that in IR spectra of vacuum- deposited poly-para-phenylene (PPP) film an extremely strong band at 1375 cm-1 is observed, which is not typical of currently known PPP modifications. High intensity of the band at 1375 cm-1 was associated with the change in the bond order of the 'defect' C-C bond between adjacent quinoid and benzenoid units. Mechanism of quinoid fragments formation in process of PPP film grows is here suggested. The p- phenylene radicals generated during thermal destruction of PPP powder are extremely active. However, when they appear included in the solid phase, they lose much of their initial reactivity, and recombination may be kinetically hindered. In this case, the macromolecules with 'stuck' terminal phenyl radicals could form. The vacuum-deposited poly-para-phenylene solid phase exhibits high crystallinity. Therefore, the recombination of 'stuck' radicals can be essentially hampered. In this case the isomerization of 'stuck' radicals gives delocalized defects. The possibility of practical applications of vacuum-deposited PPP films with delocalized defects is discussed.
A highly sensitive photoinduced polarimetry method was applied to probe optical anisotropy of the photoexcited states in non-oriented films of nano-polyacetylene. The photoinduced absorption anisotropy was observed in both cw and transient polarization experiments. The photoinduced dichroism parameter of the nano-polyacetylene films, (mu) equals (forula available in paper) was measured on the sub-nanosecond time scale ((mu) approximately equals 1) and on the millisecond time scale ((mu) approximately equals (formula available in paper) are the absorption indexes of the linear polarized probe polarized along and across the linear polarized pump, correspondingly. We discuss delocalization of (pi) electrons in the photoexcited states of trans-nano-polyacetylene chains.
New highly-ordered compositions of nanopolyacetylene (NPA) were recently synthesized. These compositions are highly stable and could be prepared in the form of solutions, films or fibers. Raman scattering in NPA exhibits high intensity of Stokes and anti-Stokes lines; long sequence of overtones and combination bands; extremely low intensity of fluorescence, and passband in the near-IR region. These properties of trans-NPA compositions suggest many important practical applications of this polymer as key photonic material for development of new types of Raman shifters.
The evolution of off-resonant and resonant Raman scattering spectra of cis and trans nanopolyacetylene (NPA) with change of frequency and intensity of incident laser light was studied. It was found that laser irradiation with wavelength 514.5 nm in process of Raman scattering spectra recording is accompanied by effective cis trans isomerization of approximately 50% cis - 50% trans NPA-PVB blend. The results obtained allow assuming that NPA in the initial compositions is a mixture of two types of nanoparticles.
Structure and optical properties of vacuum deposited poly- para-phenylene (PPP) films were investigated by UV-Vis absorption, luminescence, polarized luminescence, FTIR, and electron diffraction methods. It was shown that molecular structure, morphology and spectral parameters of vacuum deposited PPP films drastically depend on evaporation temperature, substrate temperature and distance of substrate from PPP powder. The increase of the evaporation temperature results both in red shift of the luminescence peaks from 480 nm at 650 degrees C to 540 nm at 800 degrees C and in considerable decrease of the photoluminescence intensity. Electron diffraction studies show that the highest degree of crystallinity of PPP films is observed for evaporation temperature 680 degrees C and support temperature 300 degrees C. These conditions yield optically anisotropic films with high luminescence intensity on various substrates. Electron diffraction and polarized optical measurements of highly oriented PPP films indicate that PPP molecules are essentially arrange perpendicularly to the surface of the support. It has been demonstrated that in FTIR spectra of highly oriented PPP films an extremely strong band at 1375 cm-1 is observed. That band is not typical for currently known PPP modifications and could be associated with change in the order of the 'defect' C-C bond between adjacent quinoid and benzenoid units.
Polymerization of acetylene on metallocomplex catalysts was studied. It was shown that morphology, stability and optical properties of polyacetylene (PA) compositions depend on the conditions of the PA solid phase formation. Using catalysts base don Re in highly viscous polyvinylbutiral solutions allows to obtain high stable compositions of trans- nanopolyacetylene (NPA) with unique optical properties. Compositions of NPA could be prepared in the form of solutions, films and plates. They are characterized by: (1) Vibrational structure of cis- and trans- bands in optical absorption spectra; (2) Absence of the low-energy peak in photoinduced optical absorption spectra; (3) Extremely low intensity of fluorescence; (4) Passband in the near-IR region; (5) High intensity of Stokes and anti-Stokes lines of the fundamentals of polyene chain in resonance and off- resonance Raman spectra. Compositions of NPA could be used as material for: (1) Different types of switches and sensors: (2) Raman lasers; (3) Micro label for security of objects and documents against forgery. Raman scattering recording instruments for NPA compositions could be designed based on standard digital camera, laser pointer, longpass filter and two or three lenses.
Compositions of highly ordered trans-nanopolyacetylene (trans-NPA) were prepared in the form of solutions, films and plates. They are characterized by the high stability and vibrational structure of the cis and trans bands in UV-Vis absorption spectra. There are five basic features that distinguish the Raman scattering by the trans-NPA compositions from the Raman scattering by the standard trans-PA modification. (1) Extremely low intensity of fluorescence at excitation in visual region. (2) The weak frequency dispersion of polyene C=C and C-C stretching bands, which is evidence for the narrow length distribution of conjugation chains. (3) The occurrence of long sequences of overtones and combination bands in room- temperature resonance and off-resonance Raman spectra. (4) High intensities of the anti-Stokes lines of the fundamentals v1 and v3 of the polyene chain. (5) Extremely high intensities of the v1 and v3 fundamentals of the polyene chain.
We present the results of steady-state photoinduced and electroabsorption spectroscopy studies in nonoriented films of highly stable soluble trans-polyacetylene. Using Kramers- Kronig analysis of the electroabsorption spectra the nonlinear third-order non-resonant susceptibility (chi) (3) ((omega) ;(omega) ,0,0) of trans-polyacetylene was estimated to be in the range of 10-9-8 esu.
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