Structure–activity studies of ferroelectric and antiferroelectric imine ligands and their square-planar complexes (original) (raw)
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Journal of Materials Chemistry, 2004
The synthesis and characterization of the mesomorphic and dielectric properties of a series of new imine-based liquid crystalline compounds that exhibit tilted SmC* phases is reported. The presence of an imino linkage within the mesogenic nucleus of these compounds is significant due to the ability of salicylaldimines to coordinate to metals. Structure-activity studies have also been carried out by varying the structural elements in the ligands. The structural variations include changing the length of the chiral chain and incorporating fluorocarbon segments in the achiral terminal chain.
Ferroelectric Behavior in Metal-Containing Liquid Crystals: A Structure-Activity Study
Journal of the American Chemical Society, 1994
The synthesis and physical characterization (thermotropic and ferroelectric behavior) of eight ortho-palladated dimers [Pd2(pL-Cl)2L*2] is reported. They are derived from chiral imines HL* (HL* = p-R10C6H&H=NC6H4-ORZ-p, with R1, R2, or both equal to (R)-or (S)-1-methylheptyl). The chiral imines, which contain one or two stereogenic centers, are not liquid crystals themselves. However, the dimeric complexes, which contain two or four stereogenic centers in their structure, exhibit both SmA and SmC* mesophases and enable the first comparative structure-activity study on metal-containing ferroelectric liquid crystals to be made. The ferroelectric properties obtained are better when there are chiral chains on the ortho-metalated aromatic rings, because the fixed conformation of these rings diminishes the chiral tail freedom, thus allowing a better coupling of molecular dipoles. The complexes with two chiral tails show important P s , , , values in the range 44-131 nC.cm-2. The complex with four chiral chains (R1= RZ = (R)-methylheptyl) is the first such compound ever reported containing four stereogeniccenters; furthermore, it shows a remarkably high Ps,,, value of 206 nC-cm-2, the highest value reported so far for a metal-containing liquid crystal.
Liquid crystalline heteronuclear complexes with a ferrocene-containing Schiffs base
Russian Chemical Bulletin, 1994
A series of new heteronuclear complexes of a ferrocene-containing Schiffs base (LH) with Ni II, Pd H, VlvO, and Fem as the central atoms has been obtained. PalL2, VOL2, FeL2CI, and [FeL2]20 complexes manifest liquid-crystalline properties and NiL 2 is nonmesomorphic. The structures of the complexes synthesized have been established by magnetic measurements and IR and ESR spectroscopy. All of them except PdL 2 are paramagnetic. The antiferromagnetic exchange interactions have been observed in the Fe IiI complexes. The correlation of liquid-crystalline properties with the geometry of the chelate centers is discussed.
A bent-shape liquid crystal compound with antiferroelectric triclinic-monoclinic phase transition
Liquid Crystals, 2003
Electro-optical and polarization current measurements on 1,3-phenylene-bis[4-(3-fluoro-4-decyloxyphenyliminomethyl)benzoate] (3F-10-O-PIMB) revealed a second order phase transition between two antiferroelectric 'smectic banana' phases. The observations show that the switching between the ferroelectric states in the higher temperature (HT) phase requires higher thresholds than in the lower temperature (LT) phase. It is hypothesized that the HT phase has a lower (triclinic, C 1 ) symmetry, than that of the LT phase (monoclinic, C 2 ). It is also shown that electric fields can induce transitions between different 'smectic banana' phases.
Liquid Crystals, 2019
We report mesomorphic properties of non-chiral liquid crystalline molecules and study the effect of lateral halogen (fluoro, chloro) substitution in the molecular core and the length of terminal chains. We have prepared nine homologue series with the molecular core substituted at different positions with respect to the ester linkage group. Additionally, we have modified the length of both terminal alkyl chains (hexyl, octyl, decyl and dodecyl) symmetrically for both terminal chains. The effects of the lateral substitution and the chain length are analysed with respect of the possibility to reduce the transition temperatures and tune the properties of presented liquid crystalline molecules.
A Ferroelectric Liquid Crystal Conglomerate Composed of Racemic Molecules
Science, 2000
We describe the design and synthesis of a ferroelectric liquid crystal composed of racemic molecules. The ferroelectric polarization results from spontaneous polar symmetry breaking in a fluid smectic. The ferroelectric phase is also chiral, resulting in the formation of a mixture of macroscopic domains of either handedness at the isotropic-to-liquid crystal phase transition. This smectic liquid crystal is thus a fluid conglomerate. Detailed investigation of the electrooptic and polarization current behavior within individual domains in liquid crystal cells shows the thermodynamically stable structure t o be a uniformly tilted smectic bow-phase (banana phase), with all layer pairs homochiral and ferroelectric (SmCsP,).