Poly third-order susceptibility

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... 

Poly(3-alkyl-a-thiophene) systems show significant third-order nonlinear susceptibilities ( ) Though, oligothiophenes have been studied for their third-order susceptibilities, accurate third-order optical nonlinearity data obtained by degenerate four-wave mixing or electric-field-induced second harmonic generation (EFISH) are difficult to attain reliably on samples with poor solubility characteristics (92MM1901). 

Laser lights with short wavelengths are important in optical data processing, and conjugated polymers are expected to be useful materials for their generation. Optical third-harmonic generation measurements have been performed for poly(phenylacetylenes) " The magnitudes of the third-order susceptibility were 7 x 10 esu for poly(phenylacetylene) and in the order of 10 -10" esu for its derivatives . ... 

The polymer had a A ,ax of 546 nm in the solid state and 462 nm in a chloroform solution, and an of 1 X 1 O. The Amax values indicated that poly(43) was highly conjugated. Conductivity of iodine-doped polymer was 100 S cm and the doped state would be stable for 10-20 years. This high doping stability was explained in terms of free-volume theory by Inganas [42]. The third order susceptibility (3oj co, CO, (o) was measured to be (4.3 1) x 10 esu on an... 

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. ... 

Aromatic poly(benzothiazole)s are thermally and thermooxidatively stable and have outstanding chemical resistance and third-order nonlinear optical susceptibility. Aromatic poly(benzothiazole)s can be spun into highly-oriented ultrahigh strength and ultrahigh modulus fibers. However, this type of polymer is insoluble in most organic solvents. Therefore, hexafluoroisopropylidene units are introduced in the polymer backbone to obtain soluble or processable aromatic poly(benzothiazole)s. 

In summary, it appears that poly silanes and polygermanes have large third order nonlinear susceptibilities, particularly for materials containing only a saturated sigma bonded polymer backbone. This is consistent with their large polarizabilities and the extensive sigma delocalization along the backbone. In some instances, the... 

Conjugated polymers satisfy these requirements and have thus emerged as the most widely studied materials for their susceptability. Some of the examples of conjugated polymers, that have been studied for their third order NLO properties, are polydiacetylenes, poly-p-phenylenevinylenes and polythiophenes. However, CVD has only been used in the case of poly-p-phenylenevinylenes (PPV) [section 3.4], although values have not been reported. An excellent review of third order nonlinear optical properties of PPV in general, can be found in literature. Recently, McElvain et al. ° reported the values of CVD polyazomethines to be... 

Poly(ferrocenylene vinylene) derivatives 68 with values of 3,000-10,000 and polydispersities of ca. 2.2-2.8 (determined by GPG) were synthesized in 1995 in high yields via a titanium-induced McMurry coupling reaction of the corresponding alkylferrocenyl carbaldehyde monomers (Equation (26)). " Gharacterization of these soluble polymers by NMR and IR revealed the presence of trans-Yinylcnc units. The UV-VIS spectra of the polymers are similar to those of the monomers and this indicates a fairly localized electronic structure in the former. The relatively limited electron localization is also reflected in the electrical and optical properties. For example, the values for iodine-doped conductivity a= 10 Scm ) and non-linear third-order optical susceptibility (x = 1-4 x 10 esu) are lower than those of linear conjugated polymers such as poly(l,4-phenylene-vinylene) (a = 2.5x 10 Scm" = 8 X 10 esu). 

The temporal response of the third-order nonlinear optical susceptibility in poly(PTS) crystal was determined by time-resolved degenerate four-wave mixing (DFWM) by Carter and coworkers. The excited lifetime T ws measured to be 1.8 0.5 ps at 652 nm in the resonant region. The values of phase relxation time T2 measures by Hattori and Kobayashi for a cast film of poly(3BCMU) were 30 and 90 fs for the respective incident... 

The polymers having delocalized r-electron in the main chain have been expected to possess extremely large third-order optical susceptibility.However, such an extended jr-electron conjugation generally rendered the polymers insoluble and infusible as well, which has seriously limited the fabrication of practical NLO devices. Recently, it was reported that the third-order nonlinear optical properties of poly(l,6-heptadiyne)s which were environmentally stable, soluble, and processable. The third-order optical nonlinearities of poly(l,6-heptadiyne)s bearing NLO active chomophores were evaluated for the first time. The third-order nonlinear susceptibility... 

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... 

Abstract The anisotropic third-order nonlinear optical susceptibility of monodomain samples of nematic solutions of poly[l,4-phenylene-2,6-benzobisthiazole], PBT, a rodlike polymer, have been studied by third harmonic generation. Corresponding measurements have also been made for isotropic solutions of PBT. A substantial off-diagonal component of X( H-3co o),co,co) is measured, resulting in the generation of an elliptically polarized third harmonic signal for a fundamental linearly polarized along the director. 

Transition metal poly-ynes have large third-order optical susceptibilities (X ) which consist of contributions from the real and imaginary parts of the third-order hyperpolarizabilities (y and y", respectively). In previous studies, various optical measurements were used to determine the nonlinear hyper-polarizabilities of the polymers.Most recently, an extensive study of the structural dependence of the hyperpolarizabilities of the platinum and palladium... 

On the other hand, many, particularly organic, substances show considerable third-order nonlinear susceptibilities for example poly acetylenes,... 

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