Third polysilanes

Thin films of this polymer generate third harmonic radiation upon irradiation at 1064 nm, believed to be due to a three-photon resonance. Thus polysilane polymers may eventually find use in laser technology. 

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. 

Table 5.5 Third-Order Non-linear Susceptibilities for Polysilanes and Some Related Polymers...

Nonlinear optical properties have recently been observed for the polysilane (PhMeSi) 132, suggesting that polysilanes may eventually find use in optical technology. Irradiation of a thin film of the polysilane at 1064 nm gave rise to efficient third-harmonic generation, while irradiation at 1907 cm-1 produced no nonlinear signal. The third-harmonic resonance is believed to be due to a three-photon process, but its origin is uncertain. Farther research will undoubtedly be carried out on this new phenomenon. 

The third-order non-linearities of polysilanes, are among the highest for materials that are transparent... 

Interestingly, cr-conjugated polymers such as polysilanes (see Chart 3.3) also exhibit remarkably large third-order susceptibilities... 

It must be noted that the values reported in the literature vary over broad ranges. Therefore, the values listed here reflect only the general behavior of several classes of compounds. It can be seen in Table 3.5 that trans-polyacetylenes (PAs) and polydiacetylenes (PDAs) exhibit the largest third-order NLO susceptibilities. The x value of cis-PA (not shown) is more than an order of magnitude smaller than that of trans-PA. Derivatives of poly-p-phenylene, poly(phenyl-ene vinylene), and polythiophene also exhibit NLO activity, but to a much lesser extent than PAs and PDAs. As pointed out above, polysilanes also possess quite large x values. This is explained by the cr-conjugation of the silicon chain, which implies a pronounced delocalization of cr-electrons. A very large x value... 

Another important class of photonic materials is polysilanes (Fig. 49.15) [217-222]. In polysilanes the delocalization of (T orbitals of the Si atom along the polymer backbone plays a significant role in their NLO properties. Their physical and chemical properties can be tailored by the choice of an appropriate substituent, which also determines the conformation of the polymer and its solubility. What is of more interest is their transparency in their NLO properties, values of a series of polysilanes are given in Table 49.9. Tables 49.10-49.13 contain y and values of some other third-order materials, namely metallophthalocyanine, bis-metallophthalocyanine, metallonaphthalocyanines, fuller-enes, and j8-carotenes. Although these molecules are not considered as polymers, they are macromolecules that have drawn a considerable amount of attention as third-order NLO materials. For example, the highly stable icosa-... 

Baumert JC, Bjorklund GC, Jundt DH, Jurich MC, Looser H, Miller RD, Rabolt J, Soorijakumaran R, Swalen JD, Twing RJ (1988) Temperature dependence of the third-order nonlinear optical susceptibilities in polysilanes and polygermanes. Appl Phys Lett 53(13) 1147-1149... 

BAUMERT J.C., BJORKLUND G.C., JUNDT D.H., JURICH M.C., LOOSER MC., MILLER R.D., RABOLT J., SOORYAKUMARAN R., SWALEN J.D. and TWIEG R.J., (1988), "Temperature Dependence of the Third Order Nonlinear Optical Susceptibilities in Polysilanes and Polygermanes" Appl. Phys. Lett., 53. 1147-1149. 

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