Core chirality based tailoring of the liquid crystalline properties of supermolecular tetrapedes (original) (raw)
Related papers
We synthesized thermotropic liquid-crystalline polyesters in which 9,10-diphenylanthracene moieties are incorporated into the main chain type of polyester forming the chiral smectic C (Sm C*). The polymers were prepared by the isopropyltitanate-catalyzed reaction of biphenyldicarboxylic acid and the corresponding diols, with different ratios of diol of 9,10-diphenylanthracene moiety to the alkane diols (1, 5, and 10 mol %) under nitrogen atmosphere. The polymers exhibited thermotropic liquid crystals despite the presence of a bulky diphenylanthracene moiety in the main chain. The circular dichroism spectra revealed that a Sm C* phase was formed in the polymer with 1 mol % of anthracene moiety, although only an Sm A phase was formed in the other polymers. This is the first example of a Sm C* polyester containing a diphenylanthracene moiety in the main chain. Furthermore, we measured the optical properties of the polymers and found that they exhibited very high fluorescent efficiency. The fluorescence spectra of the thin film differed from that of a CH 2 Cl 2 solution.
Chemistry of Materials, 2008
With 4′-cyanobiphenyl-4-yl benzoate nematogens chemically bonded to a benzene core via enantiomeric 2-methylpropyl spacers, a new series of cholesteric glassy liquid crystals has been synthesized for an investigation of structure-property relationships. Glass-forming ability, phase-transition temperatures, and stability against crystallization are affected by both the number and the position of substituent groups on the benzene ring with 1,3,5-trisubstituted system possessing the most favorable set of properties, T g at 73°C and T c at 295°C. With (S)-3-bromo-2-methylpropanol as the chiral precursor, left-handed helical stacking was observed for all the cholesteric GLCs reported herein. Films of the 1,3,5-trisubstituted and meta-disubstituted systems show a selective reflection wavelength, λ R , at 413 and 422 nm, respectively, whereas that of the ortho-isomer exhibits a λ R at 860 nm. Replacing one of the hybrid chiral-nematic mesogen in the 1,3,5-trisubstituted system by a nematogen loosens the helical pitch to yield a λ R at 630 nm, still shorter than that of the ortho-isomer despite the dilution by a nematogen. This observation suggests the importance of regioisomerism to helical twisting. The difference in λ R was interpreted in terms of molecular packing involving chiral spacers through computational chemistry. The susceptibility of cholesteric GLCs to photoalignment was tested using the ortho-isomer. The degree of photoalignment improves with an increasing rotational mobility of pendant coumarin monomers to an extent comparable to mechanical alignment on conventional rubbed polyimide films.
Chemistry of Materials, 2007
A novel approach to designing liquid crystal dimers with high chirality is described. The synthesis, and liquid crystal properties of several new optically active unsymmetrical fluorescent dimers belonging to four homologous series are presented. These new oligomesogens possess pro-mesogenic cholesterol as a chiral moiety covalently linked to a fluorescent bent aromatic (chalcone) core through a trimethylene (4-oxybutanoyl)/tetramethylene (5-oxypentanoyl)/pentamethylene (6-oxyhexanoyl)/heptamethylene (8oxyoctanoyl) central spacer giving rise to four series of chiral dimers. In each series, the chalcone entity is substituted with ethoxy, n-butyloxy to n-dodecyloxy tails, with the aim of learning the relation between the molecular structure and thermotropic behavior. The molecular structures have been characterized by routine characterization techniques. These compounds are fluorescent, as evidenced by recording the emission spectra for two different excitation maxima for some representative compounds. The mesomorphic properties of these dimers have been evaluated by polarizing microscopic and calorimetric studies; for some representative samples, the X-ray diffraction studies has also been carried additionally. Except one, all other compounds exhibit liquid crystal behavior. Within the homologous series comprising trimethylene, pentamethylene, and heptamethylene central spacer, compounds with short hydrocarbon tails exhibit chiral nematic phase and blue phase, whereas the members with intermediate spacer length (but for few exceptions) show the twist grain boundary and/or smectic A phase/s in addition. The thermal behavior of the higher members of these series seems to be dependent on the length of the central spacer. A similar trend was observed for lower and higher homologues of dimers possessing tetramethylene (5-oxypentanoyl, C5, i.e., odd spacer) spacer. Interestingly, the higher homologues of this series were found to exhibit two twist grain boundary phases consecutively, occurring over a relatively wide thermal range with a new phase sequence. Thus, the occurrence of a fluid frustrated phase, in particular, the blue phase in the majority of the dimers, indicates that chirality of these mesogens is high enough such that the helical pitch of the chiral nematic phase is sufficiently short. This behavior can be attributed to the presence of the bent-core chalcone entity in the dimer structure, which enhances the biaxiality and chirality of the system.
Review Chiral Liquid Crystals: Structures, Phases, Effects
2014
The introduction of chirality, i.e., the lack of mirror symmetry, has a profound effect on liquid crystals, not only on the molecular scale but also on the supermolecular scale and phase. I review these effects, which are related to the formation of supermolecular helicity, the occurrence of novel thermodynamic phases, as well as electro-optic effects which can only be observed in chiral liquid crystalline materials. In particular, I will discuss the formation of helical superstructures in cholesteric, Twist Grain Boundary and ferroelectric phases. As examples for the occurrence of novel phases the Blue Phases and Twist Grain Boundary phases are introduced. Chirality related effects are demonstrated through the occurrence of ferroelectricity in both thermotropic as well as lyotropic liquid crystals. Lack of mirror symmetry is also discussed briefly for some biopolymers such as cellulose and DNA, together with its influence on liquid crystalline behavior.
Sugar Amphiphiles as Revealing Dopants for Induced Chiral Nematic Lyotropic Liquid Crystals
Journal of Colloid and Interface Science, 2001
The existence of phase chirality in lyotropic liquid crystals still raises questions. The mechanisms behind the transfer of chirality throughout the long-range orientational order are not yet obvious. Guest/host systems with chiral dopants in achiral host phases offer the capability of systematic investigations. We demonstrate that the large amount of accessible sugar amphiphiles exhibits remarkable structure/property relations. Their helical twisting power HTP increases strongly with the number of sugar units of a dopant molecule. The spatial range of the chirality information reaching from a chirally doped micelle to adjacent aggregates is essential for the development of phase chirality. The induced twist of the lyotropic nematic host phase is highly sensitive to small changes of the sugar type (e.g., galacto-to glucopyranose). Depending on the nature of the host phase, either the αor the β-linkage of the sugar to the hydrophobic moiety of the sugar dopant results in larger HTP values. We propose that our amphiphilic sugar derivatives act like antennae to transfer chirality information. Their effectiveness as chiral dopants is due to a hydrophobic anchoring within the micelles and an extension of their chiral moiety far into the intermicellar region. The chirality transfer works especially well if the hydrophilic and chiral sugar moieties are oriented toward a neighboring micelle in the direction of the helix axis.
Chiral Liquid Crystals: Structures, Phases, Effects
Symmetry, 2014
The introduction of chirality, i.e., the lack of mirror symmetry, has a profound effect on liquid crystals, not only on the molecular scale but also on the supermolecular scale and phase. I review these effects, which are related to the formation of supermolecular helicity, the occurrence of novel thermodynamic phases, as well as electro-optic effects which can only be observed in chiral liquid crystalline materials. In particular, I will discuss the formation of helical superstructures in cholesteric, Twist Grain Boundary and ferroelectric phases. As examples for the occurrence of novel phases the Blue Phases and Twist Grain Boundary phases are introduced. Chirality related effects are demonstrated through the occurrence of ferroelectricity in both thermotropic as well as lyotropic liquid crystals. Lack of mirror symmetry is also discussed briefly for some biopolymers such as cellulose and DNA, together with its influence on liquid crystalline behavior.
A new synthetic approach based on (−)-menthone for chiral liquid crystals
Liquid Crystals, 2004
Starting from (2)-menthone, a new chiral building block useful for liquid crystal preparation was synthesized. This chiral moiety was attached to selected phenols under mild conditions by esterification. Rigid cores of tolanebenzoates and phenylbenzoates were prepared using the palladium cross-coupling reaction or by traditional liquid crystal synthesis methods. This convergent approach ended with a second esterification or palladium cross-coupling reaction to furnish new liquid crystal materials with smectic A, smectic C* and N* phases, as well as blue phases (BP). Thermal behavior, and the effect of chiral moiety branches and molecular packing in the smectic phases, have been investigated using differential scanning calorimetry, optical microscopy and X-ray diffraction.
New chiral liquid crystal with unconventional dioxane terminal unit
Phase Transitions
While designing new chiral self-assembling materials, i.e. those possessing the liquid crystalline behaviour, special attention should be paid to the specific architecture of different molecular parts, in particular: molecular core, linkage groups, type and place of the lateral substituents, structure of the chiral centre and the chiral and non-chiral chains. For the first time a new chiral photosensitive liquid crystalline compound possessing an unconventional 1,3-dioxanylmethyl terminal unit attached to the non-chiral chain has been designed and synthesized. On cooling from the isotropic phase, the material possesses only one tilted liquid crystalline phase, namely the smectic I* phase with hexagonal ordering. The crystal phase has been detected at lower temperatures. The self-assembling and structural behaviour have been studied by different techniques and compared to that of the materials with similar molecular structure but possessing structurally different terminal units in th...
Chiral liquid crystalline compounds from D-(+)-Glucose
Tetrahedron, 1995
Absrracf : D-(+)-Glucose was used as a starting material to prepare four potentially useful chiral liquid crystalline molecules 2, 3, 4 and 5 having multiple chiml centers in their rigid cores. It is clear that 2 indeed incorporates properties essential for ferroeleceic liquid crystals, i.e., a chiral smectic C phase with an induced spontaneous polarization of about 23 nC/cm*. Compound 3, on the other hand, shows only a nematic phase, while 4 merely shows a sharp melting point and 5 is an oil.