The effect of substituents on the helical twisting power of aldol condensation products of menthone

\u3cp\u3eThe helical twisting powers of the E-isomers of aldol condensation products of menthone and aromatic aldehydes are higher than those of the Z-isomers. In order to find out which chiral centre of these menthone derivatives is responsible for the value of the helical twisting in both isomers, the E-isomers of aldol condensation products of 3-methylcyclohexanone and 2-isopropylcyclohexanone were prepared and photoisomerized to form Z-isomers. The physical properties of these species were determined. It was concluded that the strong helical twisting power of the E-isomers of the derivatives of menthone is caused by the chiral carbon atom containing the methyl group in the ring. The relatively low helical twisting power of the Z-isomers and the composition of the E-Z isomers in the photostationary state are determined mainly by the other chiral centre containing the isopropyl group.\u3c/p\u3

Isosorbide derivatives

\u3cp\u3eThe invention pertains to an isosorbide derivative having at least one polymerizable group, characterized in that the isosorbide derivative further comprises at least one photo-convertible group for adjusting the helical twisting power of the isosorbide derivative. According to a preferred embodiment the isosorbide has the formula wherein A stands for a bond or a p-phenylene group; B and B' are independently O>X o2o32<or a C=O group; Q and Q' are independently selected from H, C1-C3 alkyl, C1-C3 alkoxy, halogen, and CN;n is an integer from 1 to 3; and m is an integer from 0 to 2.\u3c/p\u3

Synthesis and properties of photoisomerizable derivatives of isosorbide and their use in cholesteric filters

\u3cp\u3eThis paper describes the synthesis of photoisomerizable derivatives of isosorbide. These derivatives contain a stilbene or cinnamate moiety and can therefore be used as photoisomerizable chiral compounds in cholesteric liquid-crystalline mixtures. The reflection wavelength of cholesteric layers made from these mixtures is increased by UV irradiation due to the fact that the Z-isomers of these derivatives exhibit a lower helical twisting power than the corresponding E-isomers. The cinnamate derivatives are very suitable for use in cholesteric color filters that find application in liquid-crystal displays.\u3c/p\u3

Patterned retarders prepared by photoisomerization and photopolymerization of liquid crystalline films

\u3cp\u3eIsomerizable diacrylates derived from cinnamic acid are designed, synthesized and mixed with liquid crystalline diacrylates with the aim of making films with alternating birefringent and isotropic domains by applying the E - Z isomerization process at room temperature. The effects of the structure of the isomerizable-mesogenic group on the isotropization efficacy, the efficiency of the E - Z isomerization reaction, and film formation are discussed. Compounds derived from cyclohexyl cinnamate are proved to be good candidates that meet a whole set of parameters related to processing and application. These compounds exhibit a low nematic-to-isotropic transition temperature. In addition, they show no yellowing upon irradiation, unlike similar compounds derived from phenyl cinnamate. To elucidate the origin of isotropization of the film by irradiation, the pure Z -isomer is prepared by photolysis of the E -isomer and subsequent chromatographic separation of both isomers. Analysis of reference samples containing the pure isomers reveals that the decrease in transition temperature can be attributed exclusively to the E - Z photoisomerization process. Finally, thin films with alternating birefringent and isotropic parts of 100×100 μm 2 are obtained by using a combination of photoisomerization in air and photopolymerization in a nitrogen atmosphere, which is referred to as photo-patterning.\u3c/p\u3

Photoisomerizable chiral compounds derived from isosorbide and cinnamic acid

\u3cp\u3eThe syntheses of derivatives of isosorbide and cinnamic acid are described. These chiral compounds are photoisomerizable. The Z-isomers could also be obtained after irradiation of these E-isomeric cinnamic derivatives. The Z-isomers were found to have a much lower helical twisting power than the E-isomers. These compounds are very suitable for use in cholesteric colour filters for liquid crystal displays. This was investigated by functionalizing the E-isomeric derivatives with two acrylate groups. The reflection wavelength of cholesteric layers made with these diacrylates can be tuned by means of UV irradiation because the pitch of the cholesteric layer increases on isomerization to the Z-isomer. Subsequent photopolymerization results in cholesteric films with excellent thermal stability.\u3c/p\u3

Preparation of monodisperse polymer particles and capsules by ink-jet printing

\u3cp\u3eMicron-sized particles with a narrow size distribution are prepared by ink-jet printing technology. Droplets of a polymer solution are printed with the nozzle submerged into an aqueous phase. The particles are formed upon removal of the solvent for the polymer. The particle size can be accurately predicted from the initial drop size and the polymer concentration. The method is also suitable for the preparation of monodisperse capsules with a well-defined core and shell using an additional non-solvent for the polymer. Hollow capsules are prepared by removal of the non-solvent from core of the capsules using freeze-drying. This leads to gas-filled capsules with a well-defined polymeric shell and a diameter in the range of 5 μm, which may be applied as an ultrasound contrast agent.\u3c/p\u3