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Details are given of a new organic electro-optic crystal, 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole, having a reduced half-wave voltage of 370 V (approximately 8 times lower than lithium niobate). The molecular design, synthesis, and molecular characterization of this compound are outlined and a description is given of growth of 1-cm dimension crystals. These crystals have been characterized in terms of their structure, linear optical properties (refractive index, orientation of optical axes, absorption spectra), and also of their linear electro-optic (Pockels) effect. The compound crystallizes in the noncentrosymmetric space group Cc, with the molecules showing a high degree of parallelism. This structure is discussed in terms of the applicability of the crystals to different nonlinear optical effects. Calculated molecular hyperpolarizabilities are used, in conjunction with the determined crystal structure, to estimate the coefficients of the crystalline χ(2) tensor, which is dominated by the single coefficient χ333. The related dominant electro-optic coefficient, r333, is measured to be 8.7×10−11 m/V.

In this review heterocycles will therefore be considered as masked acyclic compounds.

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