Molecular crystals with nonlinear optical properties

Polymers and an Unusual Molecular Crystal with Nonlinear Optical Properties... 

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. 

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. 

F. Wudl, P. M. Allemand, G. Srdanov, Z. Ni, and D. McBranch, Polymers and an Unusual Molecular Crystal with Nonlinear Optical Properties (ACS Symposium Series, 455), American Chemical Society, Washington, D. C., 1991, p. 683. 

Liquid crystal polymers are also used in electrooptic displays. Side-chain polymers are quite suitable for this purpose, but usually involve much larger elastic and viscous constants, which slow the response of the device (33). The chiral smectic C phase is perhaps best suited for a polymer field effect device. The abiHty to attach dichroic or fluorescent dyes as a proportion of the side groups opens the door to appHcations not easily achieved with low molecular weight Hquid crystals. Polymers with smectic phases have also been used to create laser writable devices (30). The laser can address areas a few micrometers wide, changing a clear state to a strong scattering state or vice versa. Future uses of Hquid crystal polymers may include data storage devices. Polymers with nonlinear optical properties may also become important for device appHcations. 

With few exceptions, a useful nonlinear optical material will be in the solid phase for example, a single crystal or a poled polymer embedded in a film. Ironically, the quantum chemical calculations of nonlinear optical properties have for the most part been concerned with a single microscopic species. Much has been learned in this way about appropriate molecular construction, but the ultimate goal must be to investigate the nonlinear optical (NLO) properties in the solid phase. 

Zyss, J. Berthier. G. Nonlinear optical properties of organic crystals with hydrogen-bonded molecular units The case of urea. J. Chem. Phys. 1982. 77 (7). 3635. 

Chemla DS. Nonlinear Optical Properties of Organic Molecules and Crystals. Elsevier, 2012. Kanis DR, Ratner MA, Marks TJ. Design and construction of molecular assemblies with large second-order optical nonlinearities. Quantum chemical aspects. Chem Rev. 1994 94(l) 195-242. http //dx.doi.org/10.1021/ct00025a007. 

The liquid crystal mesophases provide various opportunities for thermal reorientation for instance, heating alters the pitch of cholesteric helices. Reference 14 considered nonlinear optical properties of C smectics associated with changes in the molecular orientation angle during heating. In this section we show that thermal orientation effects are also present in nonuniformly oriented nematics. 

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... 

Some quinones, having the ability to form intra- and/or intermolecular hydrogen bonds, exhibit high molecular hyperpolarizability and are third-order nonlinear optical (NLO) materials. Compound 39 has a %(3) of 5 x 10 11 esu at 1.9 pm, and is a third-order NLO material.23 The optoelectric properties of quinoid compounds correlate with their structures in crystals or on thin films.23... 

In this paper, an overview of the origin of second-order nonlinear optical processes in molecular and thin film materials is presented. The tutorial begins with a discussion of the basic physical description of second-order nonlinear optical processes. Simple models are used to describe molecular responses and propagation characteristics of polarization and field components. A brief discussion of quantum mechanical approaches is followed by a discussion of the 2-level model and some structure property relationships are illustrated. The relationships between microscopic and macroscopic nonlinearities in crystals, polymers, and molecular assemblies are discussed. Finally, several of the more common experimental methods for determining nonlinear optical coefficients are reviewed. 

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