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 μm. 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.