Non-linear optical crystals

Petrosyan, Fl.A., Karapetyan, H.A., Antipin, M.Yu., Petrosyan, A.M. Non-linear optical crystals of L-histidine salts, J. Crystal Growth. 275 (2005) el919-el925. 

M, Mortier, A, Bensalah, G, Dantelle, G, Patriarche, D, Vivien, Rare-earth doped oxyfluoride glass-ceramics and fluoride ceramics Sintesis and optical properties. Opt. Mat., 29, 1263-1270 (2005), Patterning of non-linear optical crystals in glass by laser-induced crystallization, J. Am. Ceram. Soc. 90, 699-705 (2007),... 

Table 3.4 Characteristics of UV light sources. BBO represents /3-BaB204 crystal, Bind is a non-linear optical crystal...

UV laser 257 (Ar+x2), 355 (YAGx3) Small diameter collimated light 30-100 mW/beam Depends on non-linear optical crystal, for example BBO Two axes scanning... 

Tsunekawa, T., Gotoh, T., and Iwamoto, M., New organic non-linear optical crystals of benzylidene-aniline derivative, Chem. Phys. Lett., 166, 353, 1990. 

J.M. Andre, C. Barbier, V.P. Bodart and J. Delhalle, Non linear optical properties of organic molecules and crystals. Vol. 2, D.S. Chemla and J. Zyss Ed. 

F Wudl, P-M Allemand, G Srdanov, Z Ni, and D McBranch, Polymers and an unusual molecular crystal with NLO properties, in Materials for Non-Linear Optics Chemical Perspectives, S.R. Marder, J.E. Sohn, and G.D. Stucky, Eds., American Chemical Society, Washington, 1991, pp. 683-686. 

The analysis of these 25 compounds confirms the flexibility of dpg/dpg+. It can adopt a propeller like conformation and induce the formation of chiral crystals. It establishes predominantly two-dimensional H-bonding networks with the counter ion. From the perspective of the crystal engineer, an anticlinal conformation would maximize the non-linear properties of the molecule. However the non-linear optical response depends greatly on the molecular alignment. Non-centrosymmetric dispositions have not yet been achieved for dpg with an anti-anti conformation. The best strategy to attain NLO samples is by inducing a syn-anti conformation where a propeller structure might induce a chiral disposition of molecules and thus a non-centrosymmetric order. Another successful approach is to force crystallization with a chiral counterion. 

Obviously, chirality is an essential property in molecular chemistry, and knots are exciting systems in this context. With a touch of fantasy, it could be conceived that some of the chemical processes for which chirality is essential (enan-tioselection of substrates, asymmetric induction and catalysis, cholesteric phases, and ferroelectric liquid crystals molecular materials for non linear optics...) could one day use enantiomerically pure knots. 

Of the many studies of applications of L-B films, we shall mention at last the development of non-linear optical materials. A molecule such as 4-nitro-aniline has a very large hyperpolarizability (section 7.2) and can be used in principle for frequency conversion in solution if a strong electric field is used to provide an orientation of the dipoles. There is no need for such an external field if similar molecules are used in an L-B film, and hyperpolarizability values far in excess of those of commonly used inorganic crystals have been obtained. Figure 8.24 shows two examples of the molecules used in... 

Liquid crystals with a large molecular mass are able to form a glassy state with mesomorphic behaviour. Yitzchaik and coworkers38 report about a new class of copolymers with non-linear optical properties, and a monomeric representative with a glassy metastable... 

Crystals of stoichiometric 1 1 mixtures of compounds that can complex with each other have been shown to form preferentially to pure crystals of the individual components. In some cases these crystals may have potential non-linear optical properties. An interesting example is the 1 1 mixture of p-aminobenzoic acid and 3,5-dinitrobenzoic acid. (15) A view of the crystal structure is shown in figure 3. Examination of this figure leads one to the hypothesis that the preference for the mixed crystal may be due to a) a more stable H-bonding interaction between the different benzoic acids in the hetero-dimer than in the homo-dimer b) the ability of the mixed crystal (hetero- dimers) to H-bond between their amino and nitro groups. It is likely that both of these factors play a role in the stability of the crystal structure. Calculational modelling can aid in determining the importance of these factors. 

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