Hydrogen bonds, nonlinear optical

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... 

V. A. Russell, M. C. Etter, M. D. Ward, Guanidinium para-substituted benzenesulfonates competitive hydrogen bonding in layered structures and the design of nonlinear optical materials , Chem. Mater. 1994, 6,1206-1217. 

In this paper, I propose a promising new electron acceptor of cyclobutenedione for nonlinear optical materials to prevent centrosymmetric crystal structures by the introduction of chirality and hydrogen bonding property into the acceptor itself. Compared with electron donative groups, electron acceptor is not yet well studied for nonlinear optical materials. The most commonly used electron acceptor is nitro (NO2) group. Therefore, we evaluated the possibility of cyclobutenedione as a new electron acceptor for nonlinear optical materials. One of the most simple cyclobutenediones is squaric acid. Squaric acid is known to be soluble in water and show very strong acidityQ2), as squarylium anion formed in water has a stable 2n delocalized electron system as shown below. 

Etter, M. C., Huang, K. S., Frankenbach, G. M. and Adsmond, D. (1991). Control of symmetry and asymmetry in hydrogen-bonded nitroaniline materials. In Materials for nonlinear optics, chemical perspectives (ed. S. R. Marder, J. E. Sohn and G. D. Stuckty), ACS Symposium Series, 455,446-55. [207]... 

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