Polymorphism and nonlinear optical activity in organic crystals

• Published in: Journal of crystal growth 1986-12, Vol.79 (1), p.745-751
• Main Authors: Hall, S.R., Kolinsky, P.V., Jones, R., Allen, S., Gordon, P., Bothwell, B., Bloor, D., Norman, P.A., Hursthouse, M., Karaulov, A., Baldwin, J., Goodyear, M., Bishop, D.
• Format: Article
• Language: English
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/0022-0248(86)90549-X

There is much current interest in nonlinear optical materials for use in optical signal processing and in optical communications. It has been shown that organic materials have advantages over the inorganics used at present. Bulk single crystals of these efficient organic materials will have applications for example as electrooptic modulators and for second harmonic generation. Although many materials have been identified that have high molecular nonlinearities, the attainment of the above second-order effects requires favourable alignment of the molecules within the crystal structure. In particular if the crystal structure is centrosymmetric then the crystalline nonlinearity is zero. In studies of organic crystals carried out within this JOERS consortium, it has been found that many of the materials have more than one possible crystal form, and that in several cases both centrosymmetric and noncentrosymmetric forms exist. Crystal growth and structure determination are described for several such polymorphic materials, along with measurements of their nonlinear optical activity. Conclusions are drawn relating to the future study and crystallisation of further materials.