Materials with nonlinear optical

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. 

The cadmium chalcogenide semiconductors (qv) have found numerous appHcations ranging from rectifiers to photoconductive detectors in smoke alarms. Many Cd compounds, eg, sulfide, tungstate, selenide, teUuride, and oxide, are used as phosphors in luminescent screens and scintiUation counters. Glass colored with cadmium sulfoselenides is used as a color filter in spectroscopy and has recently attracted attention as a third-order, nonlinear optical switching material (see Nonlinear optical materials). DiaLkylcadmium compounds are polymerization catalysts for production of poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVA), and poly(methyl methacrylate) (PMMA). Mixed with TiCl, they catalyze the polymerization of ethylene and propylene. 

The crude product is at once purified according to the usual methods of organic chemistry. Then it is essential to lower the impurities rate to a threshold compatible with crystal growth and especially with the use of the materials for nonlinear optics (10 to 100 parts per million). 

With the burgeoning of interest in this field, the publication of this book is very timely. An effort was made to include contributions from all the major research efforts in the world concerned with the development of organic and polymeric materials for nonlinear optical applications. The chapters in this book serve as a comprehensive view of the state of the art in this field, yet sufficient introductory and review material is included to render it useful for researchers interested in entering this field. 

New Polymeric Materials with Cubic Optical Nonlinearities Derived from Ring-Opening Metathesis Polymerization... 

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. 

LeBozec and co-workers have reported nonlinear behavior in a series ofterpyri-dyl and dipicolinic acid complexes, with further studies on these complexes by Maury and co-workers [83, 84]. Their research was on new molecular materials for optoelectronics, with studies based on octupolar nonlinear optical molecules showing that molecular quadratic hyperpolarizability values were strongly influenced by the symmetry of the complexes [85]. Other studies on organic-lanthanide complexes with nonlinear optics have also reported second- and third-harmonic generation behavior with simultaneous multiphoton absorption properties [50]. Such studies have shown the importance of coordination chemistry as a versatile tool in the design of nonlinear materials. 

Williams DJ (1984) Organic polymeric and non-polymeric materials with large optical nonlinearities. Angew. Chem. Int. Ed. Engl. 23 690-703... 

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