Nonlinear optical properties, solid state polymers

The nonlinear absorption of Ptn acetylide chromophores has also continued to retain the interest of many researchers. Malmstrom and coworkers have recently investigated Pt-acetylide chromophores blended with solid-state polymer matrices [94], An example of such a complex is 4.7. They found that the photoluminescence properties of the blends agreed well with that of dilute THF solutions containing the Pt-acetylides. Optical power limiting experiments showed that the clamping levels for dyes nonbonded to the polymer host were about half that for dyes in the highly cross-linked solids at similar concentrations. 

This reaction, called a four-center photopolymerization, is a typical example of topochemical reactions used to prepare polymer crystals.5 The changes in higher-order structure during the reaction are shown in Table 2.5 . Various polydiacetylene crystals have also been prepared by solid-state photopolymerization of diacetylene monomer crystals, such as 1,6-dicarbazoyl-2,4-hexadiene. These syntheses have attracted considerable interest, since they can lead to organic materials of high conductivity or of nonlinear optical properties. 

Reviews G. R. Meridith, MRS Bulletin. 13(8) 24-29, (1988) A. J. Heeger and D. R. Ulrich, "Nonlinear Optical Properties of Polymers", North-Holland Press, New York, (1988) P. N. Prasad and D. A. Ulrich, "Nonlinear Optical and Electroactive Polymers", Plenum, New York, (1988) D. J. Sandman, "Solid-State Polymerization", American Chemical Society, Washington, DC, (1987) D. J. Williams, "Nonlinear Optical Properties of Organic and Polymeric Materials", American Chemical Society, Washington, DC, (1983). 

Polydiacetylenes are particularly interesting for their optical and electrical properties. For example, large third-order nonlinear optical effects can be produced. Extensive electronic conjugation is required for such behaviour and polydiacetylenes produce the largest values yet observed for example, the solid state polymer of (20) exhibits a value of esu, and the LB polymer of (10) with n = 16,m = S exhibits a non-resonant value of 4 x 10 esu. Insulating properties are... 

Most theoretical discussions for molecules concentrate on calculations of second-order nonlinear optical properties. These results can be used equally well for the design of either molecules or molecular fragments. The latter are intended for inclusion in polymers as either a solid solution or side-chains. These are discussed in detail in section 4.3, together with systems in which a crystalline phase is dispersed in a polymer matrix. In molecularly dispersed systems the incorporation and orientation of an active species in a polymer obviates the need for a non-centrosymmetric crystal structure but does require the imposition of a polar state on the polymer (e.g. with an applied electric field). Thus molecular species that as crystals are not useful as second-order nlo materials (because they adopt a centrosymmetric structure) may be applicable in a polymeric system. Though it has received less attention in the past, considerable effort has recently been devoted to theoretical studies of... 

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