Materials with nonlinear optical properties

In the field of polymer chemistry the regio- and stereoselectivity of the Diels-Alder reaction is used for the concerted synthesis of structurally homogeneous double-stranded ladder polymers [39], which are useful materials with nonlinear optical properties and high electrical conductivity. It has turned out that the repeated Diels-Alder method is superior to an alternative two-step process, in which first an open chain precursor is formed followed by polymer ring closure as structural defects can occur [40]. 

The study of chiral materials with nonlinear optical properties might lead to new insights to design completely new materials for applications in the field of nonlinear optics and photonics. For example, we showed that chiral supramolecular organization can significantly enhance the second-order nonlinear optical response of materials and that magnetic contributions to the nonlinearity can further optimize the second-order nonlinearity. Again, a clear relationship between molecular structure, chirality, and nonlinearity is needed to fully exploit the properties of chiral materials in nonlinear optics. 

The theoretical models discussed above indicate that the sulfonyl group, although slightly weaker in electron acceptor strength, is indeed a viable alternative to the nitro group. In particular, sulfonyl derivatives of stilbene and azobenzene display large molecular hyperpolarizabilities and can be used as bifunctional chromophores for the construction of materials with nonlinear optical properties. 

Self-assembly is essentially chemical fabrication. Like macroscale fabrication techniques, self-assembly allows a great deal of design flexibility in that it affords the opportunity to prepare materials with custom shapes or morphologies. The advantages of self-assembly include an increased level of architecture control and access to types of functionality unobtainable by most other types of liquid-phase techniques. For example, it has been demonstrated that materials with nonlinear optical properties (e.g., second harmonic generation), which require noncen-trosymmetric structures, can be self-assembled from achiral molecules. 

Both TCSPC and frequency-domain fluorimetry are limited in time resolution by the response of available detectors, typically >25 ps. For cases in which higher time resolution is needed, fluorescence up-conversion can be used (22). This technique uses short laser pulses (usually sub-picosecond) both to excite the sample and to resolve the fluorescence decay. Fluorescence collected from the sample is directed through a material with nonlinear optical properties. A portion of the laser pulse is used to gate the fluorescence by sum frequency generation. The fluorescence is up-converted to the sum frequency only when the gate pulse is present in the nonlinear material. The up-converted signal is detected. The resolution of the experiment therefore depends only on the laser pulse widths and not on the response time of the detectors. As a result, fluorescence can be resolved on the 100-fs time scale. For a recent application of fluorescence up-conversion to proteins, see Reference 23. 

F Wudl, P-M Allemand, G Srdanov, Z Ni, D McBranch. Polymers and an unusual molecular crystal with nonlinear optical properties. In SR Marder, J Sohn, GD Stucky, eds. Materials for Nonlinear Optics Chemical Perspectives. ACS Symposium Series 455 683, 1991. 

The synthesis of fullerene-containing polymers is noteworthy for several reasons. On the one hand, once Cgg is attached to a polymer, most of the fullerene properties are transferred to the polymer. Thus, for instance, electroactive and photoactive polymers or polymers with nonlinear optical properties can be prepared. On the other hand, hardly processible fullerenes embedded in highly soluble polymers may become more easily amenable to further treatments. The resulting materials might eventually be used for surface coating, photoconducting devices, or to create new molecular networks. 

Hoss. R. Konig, O. Kramer-Hoss. V. Berger. U. Rogin. P. Hulliger. J. Crystallization of supramolecular materials Perhydrotriphenylene (PHTP) inclusion compounds with nonlinear optical properties. Angew. Chem. Int. Ed. Engl. 1996. 35. 1664-1666. 

Wudl, E, Allemand, P.-M., Srdanov, G., Ni, Z., and McBranch, D., Polymers and unusual molecular crystal with nonlinear optical properties, in Materials for Nonlinear Optics Chemical Perspectives, (S. R. Marder, J. E. Sohn, and G. D. Stucky, eds.). Am. Chem. Soc. Symp. Sen, 455(ACS), American Chemical Society, Washington, DC, 1991, pp. 683-686. 

In the past, a large number of trivalent boron-containing compounds—in this case the boron acts as an electron acceptor because of its vacant p-orWtal— with nonlinear optical properties have been prepared and investigated as well. Also zwitterionic molecules with tetracoordinate negatively charged borate as an electron donor seem to be interesting materials for NLO. 

Optical properties of cyanines can be usefiil for both chiral substituents/environments and also third-order nonlinear optical properties in polymer films. Methine-chain substituted die arbo cyanines have been prepared from a chiral dialdehyde (S)-(+)-2-j -butylmalonaldehyde [127473-57-8] (79), where the chiral properties are introduced via the chiral j -butyl group on the central methine carbon of the pentamethine (die arbo cyanine) chromophore. For a nonchiral oxadicarbocyanine, the dimeric aggregate form of the dye shows circular dichroism when trapped in y-cyclodextrin (80). Attempts to prepare polymers with carbocyanine repeat units (linked by flexible chains) gave oligomers with only two or three repeat units (81). However, these materials... 

Crystals with one of the ten polar point-group symmetries (Ci, C2, Cs, C2V, C4, C4V, C3, C3v, C(, Cgv) are called polar crystals. They display spontaneous polarization and form a family of ferroelectric materials. The main properties of ferroelectric materials include relatively high dielectric permittivity, ferroelectric-paraelectric phase transition that occurs at a certain temperature called the Curie temperature, piezoelectric effect, pyroelectric effect, nonlinear optic property - the ability to multiply frequencies, ferroelectric hysteresis loop, and electrostrictive, electro-optic and other properties [16, 388],... 

On the other hand, the nonlinear optical properties of nanometer-sized materials are also known to be different from the bulk, and such properties are strongly dependent on size and shape [11]. In 1992, Wang and Herron reported that the third-order nonlinear susceptibility, of silicon nanocrystals increased with decreasing size [12]. In contrast to silicon nanocrystals, of CdS nanocrystals decreased with decreasing size [ 13 ]. These results stimulated the investigation of the nonlinear optical properties of other semiconductor QDs. For the CdTe QDs that we are concentrating on, there have been few studies of nonresonant third-order nonlinear parameters. 

Again a distorted tetrahedral coordination of Hg is achieved in the l,l-bis(diphenylphos-phino)ferrocene (dppf) complex with Hgl2. Both Hg—P in the dppf chelate ring and terminal Hg—I bonds (averages 256.5 pm and 277.6 pm, respectively) are clearly longer than in the previous examples all angles around Hg are close to the value for a tetrahedron. Nonlinear optical properties of the material have been studied.241... 

The results of this research combined with the growing literature on structure-property relations in organic materials is moving us closer to the ultimate goal of developing a predictive capability for the nonlinear optical properties of molecules. 

Before being able to study the nonlinear optical properties of any material, it is necessary to have a complete understanding of its linear optical properties. Therefore, we start this section with a brief discussion of the techniques used to measure some of the most important linear properties, e.g., linear absorption, fluorescence, anisotropy, and fluorescence quantum yield. 

The linear and nonlinear optical properties of one-dimensional conjugated polymers contain a wealth of information closely related to the structure and dynamics of the ir-electron distribution and to their interaction with the lattice distorsions. The existing values of the nonlinear susceptibilities indicate that these materials are strong candidates for nonlinear optical devices in different applications. However their time response may be limited by the diffusion time of intrinsic conjugation defects and the electron-phonon coupling. Since these defects arise from competition of resonant chemical structures the possible remedy is to control this competition without affecting the delocalization. The understanding of the polymerisation process is consequently essential. 

This paper will review the linear and nonlinear optical properties of polydiacetylenes with an emphasis on our work with the nBCMU polymers. The following section will discuss material... 

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