| 摘要 |
The present invention provides a novel chemical substance suitable for practical organic nonlinear optical element having a high nonlinear optical effect, a process for the preparation thereof, and a nonlinear optical element prepared from such a chemical substance. A novel cyclobutenedione derivative prepared in accordance with the following reaction formula, a process for the preparation thereof, and a nonlinear optical element comprising such a derivative are provided: <IMAGE> +TR <IMAGE> wherein Z represents an oxygen atom or a sulfur atom; R1 represents an alkyl group, an alkenyl group or an alkynyl group; R2 represents a hydrogen atom, an alkyl group, an alkenyl group or an alkynyl group; and C* represents an asymmetric carbon atom, with the proviso that R1 and R2 may be connected to each other to form a methylene chain and that the hydrogen atom(s) in R1 may be substituted by a halogen atom, an alkyloxy group or a cyano group.
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