Synthesis and mesomorphic properties of fluorinated Schiff's base liquid crystals containing vinyl end groups

Three kinds of fluorinated Schiff＇s base esters, 4-allyloxy-2-X-6-X-benzoic acid 4-[（2, 3, 4-trifluorophenylimino）methyl]phenyl ester, where X=H or F, were synthesized and characterized. Their chemical structures were identified by Fourier transform infrared spectroscopy （FTIR） and ^1H nuclear magnetic resonance （^1H NMR）. Their mesomorphic properties were studied by polarized optical microscopy （POM） and differential scanning calorimetry （DSC）. It was found that all the three compounds exhibited enantiotropic nematic phases only. And their cleating point temperature and thermal range of mesophase decreased with the number of fluorine atoms on the rigid core of the compounds; while their melting point temperature showed no distinct regularity.

Influences of nanoparticles and chain length on thermodynamic and electrical behavior of fluorine liquid crystals

Hydrogen-bonded polar nematic liquid crystal series with the general formula n OBAF(n = 7-12) is studied. The mesomorphic characterization is demonstrated through differential scanning calorimetry(DSC) and polarized optical microscopy(POM). The complexes with short alkyl chains(n = 7, 8) present a wide nematic range and monotropic smectic F mesophase, whereas the longer alkyl chain(n = 10-12) analogues show high melting and low clearing mesomorphic liquid crystals. The thermal range of the mesophase and the birefringence increase with chain length decreasing. Furthermore, the effect of the nanoparticles(LiNbO_(3)) on the thermal and the electrical behavior of 8OBAF are investigated. The presence of LiNbO_(3) nanoparticles increases the conductivity and reduces the resistivity of the complex.

Effect of fluorine groups and different terminal chains on the electro-isomerization of azobenzene liquid crystals

A series of azobenzene liquid crystals with one or two terminal acrylate groups were synthesized and their polymers were fabricated.The azobenzene liquid crystals and their polymers achieved the photoisomerization from the liquid crystalline trans-isomer to the isotropic cis-isomer with UV irradiation.Then,the cis to trans isomerization induced by an electric field was studied,the time required for electro-isomerization was measured,the texture change and absorption variation from cis to trans form induced by the electric field were observed clearly,and the time required for electro-isomerization was much shorter than that for thermal relaxation.The influence of the polar group（fluorine）,terminal acrylate group,and flexible alkyl chain on the time of electro-isomerization was studied.The results show that the compounds with polar fluorine group require shorter time for electro-isomerization and the polymerization of terminal acrylate group delays the electro-isomerization.

Molecular structure on the detoxification of fluorinated liquid crystal monomers with reactive oxidation species in the photocatalytic process

Fluorinated liquid crystal monomers(LCMs)are begun to emerge as new persistent organic pollutants.Herein,the structure-reactivity relationships of fluorinated LCMs 1,2,3-trifluoro-5-[3-(3-propylcyclohexyl)cyclohexyl]benzene(TPrCB),1,2-difluoro-4-[trans-4-(trans-4-propylcyclohexyl)cyclohexyl]benzene(DPrCB),4-[(trans,trans)-4'-(3-Buten-1-yl)[1,10-bicyclohexyl]-4-yl]-1,2-difluoro-benzene(BBDB)and 1-[4-(4-ethylcyclohexyl)cyclohexyl]-4(trifluoromethoxy)benzene(ECTB)subject to photocatalysis-generated oxidation species were investigated.The degradation rate constant of BBDB was 3.0,2.6,and 6.8 times higher than DPrCB,TPrCB and ECTB,respectively.The results reveal that BBDB,DPrCB and TPrCB had mainly negative electrostatic potential(ESP)regions which were vulnerable to electrophilic attack by h^(+),·OH and·O_(2)^(-),while ECTB was composed of mainly positive ESP regions which were vulnerable to nucleophilic attack by·OH and·O_(2)^(-).The detoxification processes of BBDB,DPrCB and TPrCB included carbon bond cleavage and benzene ring opening.However,the methoxy group of ECTB reduced the nucleophilic reactivity on the benzene ring,leading to slower detoxification efficiency.These findings may help to develop LCMs treatment technologies based on structure-reactivity relationships。

Synthesis and photoswitching properties of azobenzene liquid crystals with a pentafluorobenzene terminal

The fluorine-substituted benzoate ester rod-shaped liquid crystals containing an azobenzene side chain linked with terminal double bonds were synthesized and characterized.The mesophase and photoswitching properties were determined by polarizing optical microscopy（POM）,differential scanning calorimetry（DSC） and UV-visible spectrometry.The rod-shaped compound 4a having an odd number of carbon atoms in the alkyl chains exhibits nematic phase and SmA type phase whereas compound 4b having an even number of carbon atoms showed only nematic phase.Both fluorinecontaining compounds 4c and 4d showed only SmA type phases.The photoswitching properties of these compounds showed a rate of trans to cis isomerization ranging 19-20 s,whereas reverse process took around 230 min in solution.These materials may be ideal in the field of optically rewritable applications where both on and off rates should be crucial.