Polyacetylenes third-order susceptibilities

Large third order susceptibilities have recently been observed for trans-polyacetylene, heteroaromatic polymers, and poly[p-phenylene vinylene] (4-11). Such nonlinear phenomena in electroactive polymers due to intense laser irradiation has been linked to the photogeneration of charged solitons on time scales of the order 10 s, and values of (3w-w+w+w)—4x 10 esu for... 

The highest value of 7 found in a study of quadrupolar examples (THG at 1,907 nm) was 229 x 10 esu for 225, which was the longest system studied. The third-order susceptibility, (DFWM, 532 nm), for the polymer, 226, was found to be over 1,000 times that of all-trans polyacetylene, although this value is presumably dispersion enhanced and very far from the static value. " ... 

Conjugated polymers and polymeric systems like polydiacetylene, polyacetylene, poly(arylene vinylene), polythiophene, polyaniline, polyimides, and polyesters have been widely studied for their third-order susceptibility. " In addition to pure polymeric systems, investigations of third-order nonU-neatity have also been carried out on small molecules, polymer-doped systems, hybrid inorganic-organic systems, and organometallic complexes. ... 

Sinclair and coworkersmeasured the third-order nonlinear optical susceptibility of rm 5 -polyacetylene. The measured susceptibility was 5 x 10 esu, which is comparable to the magnitude of the large nonlinear susceptibilities measured in the polydiacetylenes. 

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... 

Table 5. Substituted Polyacetylenes That Show Large Third-Order Nonlinear Optical Susceptibilities...

Third order NLO materials have potential applications such as optical switches, modulations and other nonlinear optical devices [189], Polydiacetylenes [190], polyacetylenes [191], poly(phenylene-vinylene)s [192] and polythiophenes [193] have large third-order nonlinear susceptibility % ranging from lO to 10 esu. 

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