Abstract:Novel functional polysilane homopolymers bearing ethereal groups were prepared by Wurtz coupling method. The polysilane monolayers demonstrated a unique chromic effect induced by a specific conformational and orientational change of polymer backbones at the aidwater interface.
“…The dichroic ratio was 4.5, which was observed to be independent of the dipping speed and the layer number. Similar anisotropy has been also observed at the air−water interface of helical polysilanes with substituents of ether and branched achiral alkyl group. , 2 Polarized absorption spectra of (a) the spin-coated film and (b) the LB film of the chiral polysilane. Solid and dashed lines represent the spectra polarized parallel and perpendicular to the dipping direction, respectively.…”
Section: Resultssupporting
confidence: 54%
“…Langmuir−Blodgett (LB) technique has been considered as a canonical method of the fabrication of thin films with the structures defined at the molecular level. During the past few decades there have been numerous studies on the fabrication, structural characterization, and functions in the LB films. − As an advantage for the LB method, anisotropic LB films have been obtained for various π-conjugated polymers such as poly(diacetylene), polythiophene, , poly( p -phenylenevinylene), and poly( p -phenylene), and σ-conjugated polysilanes, − in which polymer backbone lies along the dipping direction.…”
Thin films of a helical polysilane with chiral substituents were fabricated using a Langmuir-Blodgett (LB) method. The polarized absorption and photoluminescence spectra show the high anisotropy for the LB films with the polymer backbone lying in-plane along the dipping direction. The anisotropy of the lowest exciton absorption band can be enhanced by annealing the LB films. With use of the oriented LB film, we have revealed the one-dimensional exciton structures characteristic of polysilanes with helical conformations by measurements of electroabsorption spectra, compared with those of polysilanes of other conformations such as trans-planar and alternating trans-gauche backbone structures. The large binding energies of the lowest exciton are generic in the one-dimensional regular polysilanes, irrespective of the conformations.
“…The dichroic ratio was 4.5, which was observed to be independent of the dipping speed and the layer number. Similar anisotropy has been also observed at the air−water interface of helical polysilanes with substituents of ether and branched achiral alkyl group. , 2 Polarized absorption spectra of (a) the spin-coated film and (b) the LB film of the chiral polysilane. Solid and dashed lines represent the spectra polarized parallel and perpendicular to the dipping direction, respectively.…”
Section: Resultssupporting
confidence: 54%
“…Langmuir−Blodgett (LB) technique has been considered as a canonical method of the fabrication of thin films with the structures defined at the molecular level. During the past few decades there have been numerous studies on the fabrication, structural characterization, and functions in the LB films. − As an advantage for the LB method, anisotropic LB films have been obtained for various π-conjugated polymers such as poly(diacetylene), polythiophene, , poly( p -phenylenevinylene), and poly( p -phenylene), and σ-conjugated polysilanes, − in which polymer backbone lies along the dipping direction.…”
Thin films of a helical polysilane with chiral substituents were fabricated using a Langmuir-Blodgett (LB) method. The polarized absorption and photoluminescence spectra show the high anisotropy for the LB films with the polymer backbone lying in-plane along the dipping direction. The anisotropy of the lowest exciton absorption band can be enhanced by annealing the LB films. With use of the oriented LB film, we have revealed the one-dimensional exciton structures characteristic of polysilanes with helical conformations by measurements of electroabsorption spectra, compared with those of polysilanes of other conformations such as trans-planar and alternating trans-gauche backbone structures. The large binding energies of the lowest exciton are generic in the one-dimensional regular polysilanes, irrespective of the conformations.
ABSTRACT:In the family of optically active synthetic polymers, optically active polysilanes, which comprise a helical main chain of silicon-silicon single bonds and chiral and/or achiral side groups, exhibit unique absorption, circular dichroism, and fluorescence spectra around 300-400 nm due to σ-conjugation. Since the first brief report of optically active polysilane synthesis in 1992, the field has now widened to include various homo-and copolymers of optically active poly(dialkylsilane)s, poly(dialkoxysilane)s, poly[alkyl(aryl)silane]s, and poly(diarylsilane)s. This review comprehensively covers work on (i) the relationship between side chain structure, (ii) local structure-global shape relationship, (iii) (chir)optical properties, (iv) (semi)quantitative population analysis of right-and left-handed helices based on Kuhn's dissymmetry ratio, (v) several helical cooperativity effects, (vi) molecular imaging, (vii) inversion of screw-sense, (viii) chiroptical switch and memory, (ix) transfer and amplification of molecular chirality to aggregates, (x) cholesteric liquid crystallinity, (xi) helical supramolecular structures, and (xii) latent helicity, as consequences of side group internal interactions and other external stimuli. Such knowledge and understanding may stimulate optically active polymer research in the realm of nanomaterial science and nanotechnology at the sub-nm level as well as traditional polymer science, and may advance these polymers to new functional nanomaterials and thence to the realization of nanodevices in the future.
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