Polysilane polymers nonlinear optical properties

The polysdanes are normally electrical insulators, but on doping with AsF or SbF they exhibit electrical conductivity up to the levels of good semiconductors (qv) (98,124). Conductivities up to 0.5 (H-cm) have been measured. However, the doped polymers are sensitive to air and moisture thereby making them unattractive for practical use. In addition to semiconducting behavior, polysilanes exhibit photoconductivity and appear suitable for electrophotography (qv) (125—127). Polysdanes have also been found to exhibit nonlinear optical properties (94,128). 

In addition to photoconductivity, polysilanes have been found to exhibit marked nonlinear optical properties,95-97 suggesting that they may eventually be useful in laser and other optical technology. The third-order non-linear susceptibility, X3, is a measure of the strength of this effect. The non-linear properties of polysilanes, like the absorption spectra, seem to be dependent on chain conformation and are enhanced for polymers having an extended, near anti conformation (Table 5.5). The value of 11 x 10 12 esu observed for (n-Hex2Si) below its transition temperature is the largest ever observed for a polymer which is transparent in the visible region. 

Abstract The linear and nonlinear optical properties of polysilanes, and in particular poly(di-n-hexylsilane), have been investigate by vacuum UV spectroscopy and by two-photon induced processes. The electronic structure of the polymer inferred from these measurements is consistent with models which view the polymer as a one-dimensional semiconductor quantum wire. The exciton related optical nonlinearities are also large enough to allow polysUanes to be considered for various nonlinear switching applications. 

Polysilane high polymers possessing fully saturated all-silicon backbone have attracted remarkable attention recently because of their unique optoelectronic properties and their importance in possible applications as photoresists, photoconductors, polymerization initiators, nonlinear optical materials etc. A number of review articles have been published on this topic4-9. The studies in this field have stimulated both experimental and theoretical chemists to elaborate on understanding the excited state nature of polysilanes and oligosilanes and of their mechanistic photochemistry. 

Polysilanes have proved to be an intriguing class of inorganic polymers with many versatile applications in ceramics, photoelectronics, photoresistors, and nonlinear optics.8,9 The unusual optoelectronic properties of polysilanes are attributed to sigma-conjugation of the silicon atoms in the polymer backbone chain, depending on the molecular weight, conformation, and substituents of the polymer.10a Wurtz-type... 

Polysilanes are air-stable Si-Si backbone polymers that exhibit efficient emission in the UV spectral region, high hole mobility, and high nonlinear optical susceptibility [28]. These properties arise from delocalization of a electrons along the Si-Si chain. Polysilanes have been employed as fluorescent materials for radiation detection, as electroluminescent materials for display devices, and as photorelractive materials for holographic data storage [28]. 

Even a preliminary investigation of the properties of some inorganic pol5miers reveals that some of them have unexpected properties. Polythi-azyl is an anisotropic electrical conductor and shows conductivity that is comparable to metals. At 0.26 K this polymer becomes superconducting [4, 5]. Polysilanes which contain catenated silicon atoms in a polymeric chain have several unusual properties. These polymers have a o-electron delocalization. They are radiation sensitive and many of them are thermo-chromic. Many members of this family also show nonlinear optical behavior [17, 19]. 

Examples of polymers of the type -(M-M-) containing a bond in the main chain are known with metals or semimetals like B, Si, Ge, Sn, As, Sb, Th and Po [1]. Examples are shown in 66. Well-described are polydiorganosilicones (polysilanes) which are investigated for use as precursors of B-silicon carbide, as photoconductors, in nonlinear optics and microlithography. Preparations and properties are reviewed in [1,42,271,272]. 

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