Schiff Base Mesogen Research Articles

The effects of molecular structure and functional group of a rodlike Schiff base mesogen on blue phase stabilization in a chiral system

A wider blue phase (BP) range can be induced easily when two difluoro substituted and racemic rodlike Schiff base mesogens are doped with the appropriate concentration of chiral dopants S811 or ISO(6OBA)2.

Effect of the Functional Groups of Racemic Rodlike Schiff Base Mesogens on the Stabilization of Blue Phase in Binary Mixture Systems.

Four series of rodlike racemic Schiff base mesogens possessing different alkyl chains and two types of linkages, ester and alkynyl linkages, were synthesized and applied to induce cubic blue phases (BPs) in simple binary mixture systems. The mesophases of these Schiff base mesogens were confirmed by variable-temperature X-ray diffraction and the characteristic texture from polarized optical microscopy (POM). In general, when chiral additive S-(+)-2-octyl 4-(4-hexyloxybenzoyloxy)benzoate (S811; 20-40 wt %) is added into the rodlike racemic salicylaldimine-based mesogens, the cubic BPs could be observed and its temperature range is larger than 20 K. The widest temperature range of the cubic BP (35 K) can be observed in the blending mixture composed of rodlike racemic salicylaldimine-based mesogen OH-TIn possessing alkynyl linkage and 35-40 wt % S811. However, Schiff base mesogens possessing alkynyl linkage show a direct isotropic to chiral nematic transition when equal amount of chiral dopant is added. Notably, the termination temperature of BPs is very close to room temperature (ca. 35 °C) after 40.0 wt % S811 is added into the salicylaldimine-based mesogens possessing terminal alkyl chains and ester linkage. Interestingly, wide BPs (>30 K) can also be induced by adding chiral additive 1,4:3,6-dianhydro-2,5-bis[4-(n-hexyl-1-oxy)benzoic acid]sorbitol (ISO(6OBA)2) with a high helical twisting power into the racemic Schiff base mesogen possessing ester linkage. Cubic BPI and BPII can be confirmed by reflectance spectra and POM. The results of reflectance spectra indicate that the binary mixture composed of salicylaldimine-based mesogens and S811 easily exhibits a supercooling effect and induces BPI. However, only BPII can be observed in all binary mixtures containing Schiff base mesogens. On the basis of our experimental results and molecular modeling, we suppose that the values of biaxiality, polarizability, and the dipole moment of molecular geometry are the main factors that affect BP stabilization.

Broad temperature range of cubic blue phase present in simple binary mixture systems containing rodlike Schiff base mesogens with tolane moiety.

Four simple rodlike Schiff base mesogens with tolane moiety were synthesized and applied to stabilize cubic blue phases (BPs) in simple binary mixture systems for the first time. When the chiral additive or was added into a chiral salicylaldimine-based compound, the temperature range of the cubic BP could be extended by more than 20 °C. However, when the chiral Schiff base mesogen was blended with chiral dopant possessing opposite handedness, , BPs could not be observed. Interestingly, the widest temperature range of the cubic BPs (∼35 °C) could be induced by adding the rodlike chiral dopant or into the rodlike racemic Schiff base mesogen with hydroxyl group. On the basis of our experimental results and molecular modeling, the appearance and temperature range of the BPs are affected by the dipole moment and the biaxiality of the molecular geometry. Accordingly, we demonstrated that the hydroxyl group and the methyl branch in this type of Schiff base mesogen play an important role in the stabilization of BPs.

Coumarin based emissive rod shaped new schiff base mesogens and their zinc(II) complexes: synthesis, photophysical, mesomorphism, gelation and DFT studies

ABSTRACTNew homologous series of coumarin Schiff base derived from 6-aminocoumarin and their zinc(II) complexes have been synthesised. The spectroscopic characterisations, photophysical properties, phase transition temperature, characterisation of phase and gelation behaviour are reported. The ligand is non-mesogenic at lower 4-n-alkoxy chain length (n = 4) and mesogenic for longer chains (n > 4). For small chains (n = 5, 7, 8), ligand displays monotropic nematic or nematic-smectic A phase sequences, whereas longer homologues (n = 12, 14, 16 and 18) display only enantiotropic smectic A phase. The ligands and their Zn(II) complexes are fluorescent in nature. Interestingly, ligands exhibit gelation property only in polar solvents, whereas Zn(II) complexes discourage gelation. The effect of 4-n-alkoxy chain length on the gelation properties was also discussed. Density functional theory calculations show broad agreement with observed molecular conformation, dipole moment, molecular orbitals and polarisability of the coumarin Schiff base molecules and their Zn(II) complexes.

Synthesis, characterisation and mesomorphic properties of a homologous series of oxovanadium(iv) complexes containing a bidentate [N,O] donor Schiff base mesogen

A series of oxovanadium(iv) complexes of the type [VO(L)2], [L = N-(4-n-alkoxysalicylaldimine)-4-hexadecyloxyaniline, n = 8, 10, 12, 14, 16 or 18] have been synthesised and characterised by FT–IR, 1H NMR, 13CNMR, UV–Vis, and FAB mass and magnetic susceptibility measurements. The ligands are coordinated to the vanadyl ion in a bidentate fashion. The mesomorphic behaviour of the ligands and their vanadyl complexes was investigated by polarising optical microscopy and differential scanning calorimetry. The compounds were all highly thermally stable, and their mesomorphic properties were found to depend on the length of the carbon chain. Both the ligands and their higher homologue complexes exhibited a SmC mesophase. In the case of the lower homologues the ligands exhibited the SmC phase but their complexes a SmA mesophase. The mesophase–isotropic transition temperatures for the complexes were significantly higher than those of the ligands. Variable temperature magnetic susceptibility measurements on the vanadyl complexes clearly suggested absence of any exchange interactions among the vanadyl spin centres. Cyclic voltammetry showed a quasi-reversible one-electron response at 0.51 V for the VO(iv)–VO(v) redox couple. Density functional theory studies carried out using DMol3 at the BLYP/DNP level to determine the energy-optimised structure revealed a distorted square pyramidal geometry for the vanadyl complexes, with the alkoxy tails projecting away from one another.

Schiff Base 메소젠과 Glycols 유연격자를 갖는 새로운 열방성 화합물

New Thermotropic Compounds with Schiff Base Mesogen and Glycols Flexible Spacers Bong-Keun So†, Ji-Young Song†, Soo-Min Lee†, Ok-Byung Choi, Hwan Myung Lee, Jin-Young Lee, Seong-Jo Kim, Eun-Hee Cha, Ran Hee Kim, and Joo-Hoon Park* College of Natural Science, The Research Institute for Basic Sciences, Hoseo University, Chungnam 336-795, Korea †Department of Chemistry, Hannam University, Daejeon 306-791, Korea (Received September 13, 2009; Revised November 2, 2009; Accepted December 2, 2009)

Dimesogenic liquid crystal consisting of cholesterol and Schiff base moieties: dependence of LC properties on the spacer length and fluorination of the alkoxy tails

The liquid crystalline properties of two series of non‐symmetric liquid crystal dimers consisting of cholesterol and Schiff base moieties interconnected by ω‐oxyalkanoyl spacers of varying length are compared: one series (SBOC‐ n ) carry the octyloxy tail on the Schiff base mesogen, and the other (SBOF‐ n ) a perfluoroheptylmethyloxy tail. In general, compounds with the fluorinated alkoxy tail exhibited mesophases over a much wider temperature range than those with the alkoxy tail. The latter series favoured the formation of more diverse mesophases than the former. SBOC‐4, ‐5 and ‐7, and SBOF‐4, ‐5 and ‐10 formed the chiral smectic C phase.

Smectic Mesophase Behavior of Dimeric Compounds Showing Antiferroelectricity, Frustration and Chirality

We have prepared a series of dimeric compounds, mOAM5AMOm, which comprise two Schiff's base mesogens. These compounds formed three types of fluid smectic liquid crystals. When the alkoxy tail length is short (m=4 and 6), the alkoxy tail groups mix randomly with the alkyl spacer groups, resulting in the SmCAs phase. The compounds with m longer than 14 form the SmCAb phase with a bilayer character, in which the spacer and tail groups segregate from each other and consequently two mesogenic layers (so-called bilayer) are included within a repeat unit. In such a bilayer association of twin dimers, spontaneous polarization appears in each bilayer. In this SmCAb phase, furthermore, the molecules are tilted to the layer so that chirality is spontaneously formed in addition to ferroelectricity. The structure was identified as SmCAPA type. The compounds with intermediate m of 8–12 formed the frustrated SmCAf phase with a density modulation (frustration) along the layer. On cooling from the smectic phases, crystallization takes place for mOAM5AMOm with m=4–8, while the chiral Crblue phase with the TGB-like helical structure was clearly identified with m=14–18. The structure and properties of these exotic phases in twin dimers are described in detail.

Ferroelectric Liquid Crystals from Bent-Core Molecules with Vinyl End Groups

New banana-shaped achiral compounds, 1,3-phenylene bis [4-{4-(alkenyloxy) phenyliminomethyl}benzoate]s were synthesized by varying the length of alkenyl group; their ferroelectric properties are described. The smectic mesophases, including a switchable chiral smectic C <TEX>$(Sm\;C^*)$</TEX> phase, were characterized by differential scanning calorimetry, polarizing optical microscopy and triangular wave method. The presence of vinyl groups at the terminals of linear side wings in the banana-shaped achiral molecules containing Schiff's base mesogen induced a decrease in melting temperature and formation of the switchable <TEX>$(Sm\;C^*)$</TEX> phase in the melt. The smectic phases having the octenyloxy group such as <TEX>$(CH_2)_6CH=CH_2$</TEX> showed ferroelctric switching, and their values of spontaneous polarization on reversal of an applied electric field were 120 nC/cm² (X=H) and 225 nC/ cm² (X=F), respectively. We could obtain ferroelectric phases by controlling the number of carbon atom in alkenyloxy chain of a bent-core molecule.

Dimeric liquid crystalline compounds having a central malonic acid moiety: effect of the length of the spacers and terminal chains

We have studied the liquid crystalline properties of two new series of dimeric compounds consisting of a central malonic acid moiety, polymethylene spacers, and Schiff's base mesogens. In the first series we changed the length of the spacers with the terminal chain fixed as the butoxy group; in the second series we changed the length of the terminal alkyl or alkoxy groups while keeping the spacers fixed as decamethylene groups. In the first series, as the length of the spacer increased, the tendency to form smectic phases grew. In the second series, changing the alkyl terminal chain to the alkoxy terminal group raised the melting and isotropization temperatures. Increasing the length of the terminal group diminished the temperature range for the higher temperature smectic phase. The smectic phases are assigned to be smectic A and crystal smectic E phases.

Ferroelectric liquid crystals from banana-shaped achiral molecules with vinyl end groups

Banana-shaped achiral compounds, the 1,3-phenylene bis[4-(alkenyloxyphenyliminomethyl)benzoate]s, were synthesized with varying length of the alkenyl group; their ferroelectric properties are described. The smectic mesophases, including a switchable chiral smectic C (SmC*) phase, were characterized by differential scanning calorimetry, polarizing optical microscopy and the triangular wave method. The presence of vinyl groups at the ends of the linear side-wings in the banana-shaped achiral molecules, containing a Schiff's base mesogen, induced a decrease in melting temperature and formation of the switchable SmC* phase in the melt. The compound having the octenyloxy group exhibited a spontaneous polarization of 120 nC cm−2 on reversal of an applied electric field.

Antiferroelectric liquid crystal from a banana-shaped achiral molecule

A new banana-shaped achiral compound, 1,3-phenylene bis[4-(3-fluoro-4-n-octyloxyphenyliminomethyl)benzoate] (PBFOB) was synthesized and its antiferroelectric liquid crystallinity determined. The PBFOB was characterized by differential scanning calorimetry, X-ray diffractometry in the small and wide angle regions, and polarizing optical microscopy; its polarization and antiferroelectric properties were also investigated. The presence of a lateral fluoro-substituent in the banana-shaped achiral molecules containing a Schiff's base mesogen induced a decrease in melting temperature and formation of the switchable smectic B2 phase in the melt. The spontaneous polarization for PBFOB was about 250 nC cm-2 and the polarization of this phase switched on the reversal of an applied electric field.

Smectic Mesophase Properties of Dimeric Compounds. 2. Distinct Formation of Smectic Structures with Antiferroelectric Ordering and Frustration

We have prepared two series of dimeric compounds, which comprise the schiff's base mesogen, alkyl spacer with the carbon number of 5 and alkyl or alkoxy tail with the carbon number of m = 4∼16. In these compounds, we observed three types of smectic liquid crystals, the single layer phase with the tail group randomly mixing with the spacer, the bilayer phase in which the segregation of the spacer and tail groups takes place and so two mesogenic layers are included within a repeat unit, the frustrated smectic phase in which the density modulation appears along the layer as well as the layer normal. The bilayer phase was found to be antiferroelectric and the frustrated smectic phase was considered to result from the two dimensional escape from the dipolar interaction. The phase behaviour with m and the structure and properties of each phase will be described in detail.