Morphology and polymorphism control of organic polyene crystals by tailor-made auxiliaries

Configurationally locked polyene crystals grown in the absence and in the presence of their tailor-made auxiliaries, which are slightly modified substrate molecules, were investigated. The effects of the tailor-made auxiliaries on the crystal characteristics were investigated by X-ray crystal structure analysis and nonlinear optical and photoluminescent measurements. The substrate crystals of 2-{3-[2-(4-dimethylaminophenyl) vinyl]-5,5-dimethylcyclohex-2-enylidene} malononitrile (DAT2) and 2-{3-[2-(4-pyrrolidinphenyl)vinyl]- 5,5-dimethylcyclohex-2-enylidene} malononitrile (PyT1) exhibit a strong powder second harmonic generation signal of about 140 and 80 times that of urea at a fundamental wavelength of 1.9 mu m. Although the investigated substrate polyene molecules DAT2 and PyT1 show very similar crystal structures in the absence of auxiliaries, in the presence of the tailor-made additives with the same modification of the corresponding substrate molecules, the DAT2 crystal exhibits a morphological change and the PyT1 crystal exhibits a polymorphic change.