Banana-shaped Molecules Research Articles

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.

Occurrence of the B 7 mesophase in two homologous series of seven-ring achiral compounds composed of banana-shaped molecules

The synthesis and mesomorphic behaviour of twenty compounds belonging to two new series of seven-ring esters derived from 2-cyanoresorcinol are reported. Many homologues of both series exhibit the B7 mesophase. In addition, some of the lower homologues exhibit a mesophase which shows textural features similar to that of the two-dimensional B1 phase. The characterization of the mesophases has been carried out using polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction, miscibility studies and electro-optical investigations. The first example of a plot of the B7-isotropic phase transition temperature as a function of the alkyl chain length is also reported.

Dielectric investigations on oriented phases formed by banana-shaped molecules

Dielectric investigations on a magnetically oriented sample forming N, SmA, SmC and B 2 phases were carried out. The sample shows a negative dielectric anisotropy in the N state and a strong increase of the static dielectric constants perpendicular to the director in the ensuring 'classical' phases. This proves directly the strong and continuous increase of the positive dipole correlation in the lateral direction due to the steric interactions of the bent-shape molecules. From a dynamical point of view, the SmA and SmC phases of this sample show deviations from the classical phases of rod-like molecules. Crystallization did not allow us to extend the dielectric measurements into the B 2 state.

The first liquid crystalline dimers consisting of two banana-shaped mesogenic units: a new way for switching between ferroelectricity and antiferroelectricity with bent-core molecules.

Depending on the number of dimethylsiloxane units in the spacer connecting two banana-shaped molecules either ferroelectric or antiferroelectric switchable polar smectic C phases have been obtained.

PA18 バナナ型分子によるネマチック相のダイナミクス(物理・物性)

PA18 バナナ型分子によるネマチック相のダイナミクス(物理・物性)

Helical superstructures in the mesophase of compounds derived from 2-cyanoresorcinol

The mesophase exhibited by four members of a new homologous series of compounds composed of banana-shaped molecules derived from 2-cyanoresorcinol is reported. The characteristic optical textures showing helical filamentary growth patterns, coupled with the results from X-ray diffraction studies of these seven-ring compounds containing a biphenyl moiety indicate that the mesophase is indeed B7.

Stacking of conical molecules with a fullerene apex into polar columns in crystals and liquid crystals.

Polar liquid crystalline materials can be used in optical and electronic applications, and recent interest has turned to formation strategies that exploit the shape of polar molecules and their interactions to direct molecular alignment. For example, banana-shaped molecules align their molecular bent within smectic layers, whereas conical molecules should form polar columnar assemblies. However, the flatness of the conical molecules used until now and their ability to flip have limited the success of this approach to making polar liquid crystalline materials. Here we show that the attachment of five aromatic groups to one pentagon of a C(60) fullerene molecule yields deeply conical molecules that stack into polar columnar assemblies. The stacking is driven by attractive interactions between the spherical fullerene moiety and the hollow cone formed by the five aromatic side groups of a neighbouring molecule in the same column. This packing pattern is maintained when we extend the aromatic groups by attaching flexible aliphatic chains, which yields compounds with thermotropic and lyotropic liquid crystalline properties. In contrast, the previously reported fullerene-containing liquid crystals all exhibit thermotropic properties only, and none of them contains the fullerene moiety as a functional part of its mesogen units. Our design strategy should be applicable to other molecules and yield a range of new polar liquid crystalline materials.

Determination of the second order susceptibility tensor in banana-shaped liquid crystals

Optical second harmonic generation (SHG) measurements have been carried out on the B2 phases of three liquid crystal materials composed of conventional banana-shaped molecules (P-10-O-PIMB, P-8-O-PIMB and P-8-PIMB). Quantitative values of the second order susceptibilities dij have been deduced from SHG measurements at oblique incidences on polydomain racemic samples under an electric field. The dij coefficients are in the range 1-10 pm V−1.

Banana-shaped mesogens: effect of lateral substituents on seven-ring esters containing a biphenyl moiety

The synthesis and characterization of five homologous series of symmetrical compounds composed of banana-shaped molecules containing a biphenyl moiety are reported. All these compounds are non-Schiff's bases and are esters. The effects of lateral substituents such as fluoro, methyl and ethyl in the side arms of these molecules are examined. These substituents have a strong influence in reducing the clearing temperatures. Banana phases such as B1, B2 and B6 were observed in the above series of compounds. The mesophases were characterized by a combination of polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optic studies.

Ferroelectric properties exhibited by mesophases of compounds composed of achiral banana-shaped molecules

The synthesis and mesomorphic properties of a new series of five-ring esters composed of banana-shaped molecules are reported. The homologues containing n-dodecyloxy, n-tetradecyloxy and n-hexadecyloxy terminal chains exhibit a smectic phase while that with an n-octadecyloxy chain shows a two-dimensional structure. The structures of the mesophases have been determined by X-ray diffraction studies. Interestingly both these mesophases exhibit ferroelectric properties. The electro-optical switching characteristics have been investigated using both triangular-wave and d.c. electric fields. Ferroelectricity is clearly demonstrated in both the mesophases by bistable switching behaviour.

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.

Ester-type banana-shaped monomers and investigations of their electro-optical properties

New banana-shaped monomers 1a–1f, based on the 1,3-phenylene bis{4-[4′-(alkenyloxy)benzoyloxy]}benzoate bent structure were prepared. The central 1,3-phenylene ring was either unsubstituted (1a, 1b) or had a 2-methyl substituent (1c, 1d) or a 4-chloro substituent (1e, 1f), respectively. The occurrence of mesophases greatly depended on the chemical structure of the banana-shaped molecules. Whilst 1,3-phenylene bis{4-[4′-(10-undecenyloxy)benzoyloxy]}benzoate (1b, acronym Pbis11BB) formed a monotropic B2 phase, the 4-chloro derivatives showed conventional nematic and SmC phases. In contrast, the 2-methyl derivatives did not form any kind of mesophases. MOPAC/AM1 semi-empirical calculations allowed evaluation of the value and orientation of the electric dipole vectors and of the twist angles of the central phenyl ring with respect to the outer rings. Electro-optical investigations showed that the B2 phase of 1b was antiferroelectric with a 45° tilt angle between 91–75 °C (P = 320 nC · cm−2) and a switching time in the range of 50 μs in a E = 15 V · μm−1 field. Synthetic route for the preparation of monomers 1a–1f.

Influence of fluoro substituents on the mesophase behaviour of banana-shaped molecules

Three new series of bent-shaped five-ring liquid crystals, based on the ester of isophthalic acid as the central core and azomethine linkages, are presented. They differ by the number and the position of halogeno substituents on the outer rings. This lateral substitution strongly influences the type of mesophases formed. Calculations were performed to determine the modification of the distribution of charge along the different molecules.

Liquid crystal phases of achiral banana-shaped molecules: a computer simulation study

The phase behaviour of achiral banana-shaped molecules was studied by computer simulation. The banana-shaped molecules were described by model intermolecular interactions based on the Gay-Berne potential. The characteristic molecular structure was considered by joining two calamitic Gay-Berne particles through a bond to form a biaxial molecule of point symmetry group C 2v with a suitable bending angle. The dependence on temperature of systems of N=1024 rigid banana-shaped molecules with bending angle φ =140° has been studied by means of Monte Carlo simulations in the isobaric-isothermal ensemble (NpT). On cooling an isotropic system, two phase transitions characterized by phase transition enthalpy, entropy and relative volume change have been observed. For the first time by computer simulation of a many-particle system of banana-shaped molecules, at low temperature an untilted smectic phase showing a global phase biaxiality and a spontaneous local polarization in the layers, i.e. a local polar arrangement of the steric dipoles, with an antiferroelectric-like superstructure could be proven, a phase structure which recently has been discovered experimentally. Additionally, at intermediate temperature a nematic-like phase has been proved, whereas close to the transition to the smectic phase hints of a spontaneous achiral symmetry breaking have been determined. Here, in the absence of a layered structure a helical superstructure has been formed. All phases have been characterized by visual representations of selected configurations, scalar and pseudoscalar correlation functions, and order parameters.

Side Arms Change Pitch

When a nematic liquid crystal is made up of chiral (or handed) molecules, the molecules themselves not only orient with respect to each other but can also adopt a helical pitch. Adding achiral molecules would be expected to decrease (or dilute) the twisting power of the chiral nematic and to increase the helical pitch. Thisayukta et al. examined what happened when banana-shaped molecules, with similar side arms but different central linkers, were added to a linear chiral nematic. Surprisingly, they observed an increase in the twisting power of the chiral nematic and a decrease in the optical pitch. Liquid crystals made of banana-shaped molecules (which lack an asymmetic carbon atom) have been known to form chiral smectic phases. These phases are believed to form as a result of a layering of the molecules, an inherent twisting of the side arms, or a helical twisting of the molecules about the director. In this case, the authors conclude that the chirality does not arise from how the molecules pack but instead is caused by twisting of the side arms. — MSL

Enhancement of Twisting Power in the Chiral Nematic Phase by Introducing Achiral Banana-Shaped Molecules

Achiral banana-shaped molecules with dodecyloxy tail groups, P-12-O-PIMB, N-12-O-PIMB, and S-12-O-PIMB, have exhibited unusual smectic phases which possess chiral and helical structures. In this work, we mixed these banana-shaped molecules with the chiral molecule forming a chiral nematic liquid crystal and found an exclusive effect of the achiral dopant that the twisting power of the chiral nematic phase in the mixtures is significantly increased with the increase of the content of achiral banana-shaped molecules. This characteristic effect in the chiral nematic field seems to offer the rational evidence for the twist conformation of such banana-shaped molecules, since the chirality should be included intrinsically within each chain. The asymmetric twist conformation in the ester linkage group connecting the central core with the side wings is likely to be the origin of enhanced twisting power.

Flow properties of the optically isotropic tetrahedratic phase

We discuss the coupling between flow and other hydrodynamic variables that can occur in the optically isotropic tetrahedratic phase (Td) characterized by a third rank tensor order parameter Tijk. We point out that an applied electric field or an applied temperature gradient will lead to flow. Reciprocally we predict that, for example, a shear flow applied to a tetrahedratic phase leads to an induced electric field and a temperature gradient. Similarities to recent experimental observations in the vicinity of the isotropic-B7 phase transitions in materials formed by banana-shaped molecules are discussed.

Field-Induced Behavior in a Liquid Formed by Achiral Banana-Shaped Molecules in the Vicinity of the Phase Transition Isotropic - B 2 Phase

We have experimentally investigated the electric-field effect on the Isotropic - B 2 phase transition of an achiral banana-shaped mesogen 1,3-phenyllene bis[4-(4-10-alkoxy-benoyloxy)phenyliminomethyl] ( C 11 compound) [1]. From microscopic observations under electric fields and measurements of the D-E hysteresis loops, the T (temperature) - E (electric field) phase diagram was established, in which a critical field is observed in the isotropic liquid. This field characterizes the first nucleation of a ferroelectric state noted B F induced by the electric field. The results are interpreted in the framework of a phenomenological model that describes the Isotropic - B 2 phase transition by the condensation of a vector wave directly from the isotropic liquid [2].

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.

Molecular Modelling of Bone Morphogenetic Protein-2 (BMP-2) by 3D-Rapid Prototyping

Bone morphogenetic proteins (BMP) play a decisive role in bone development and osteogenesis. In the past they have been the subject of widespread research and clinical trials as stimulants of bone growth. Recently BMP-2 has been chemically immobilized on implant surfaces leading to enhanced bone growth and accelerated integration in sheep. Although the 3D-structure of BMP-2 is known the surface topography has not been the subject of a detailed analysis. Therefore we have begun implementing the technique of 3D-rapid prototyping as a novel method for gaining topographical information on the structure-function relationship of proteins (Laub et al., 2001, FASEB J. 15, A543). 3D-rapid prototyping allows the construction of accurate three-dimensional models of proteins based on their x-ray crystallographic data. In this way we constructed a 3D scale image of BMP-2 of the size 140 mm × 70 mm × 50 mm corresponding to a ca. 20 × 106 fold magnification (scale 1 nm = 2 cm). BMP-2 is a twisted banana-shaped molecule consisting of a convex and a concave face and has a horn-like protuberance cross-turned at 180° (long axis) at each end. In the center of the convex face there is a ca. 1 nm deep crater like pit ca. 1.8 nm in diameter. The concave face is characterized by a 6–7 nm long helical groove 0.8–1.6 nm wide and ca 0.8 nm deep, into which a left-handed helix with a pitch of 8–9 nm and a helical radius of 0.35–0.45 nm can be fitted. The concave face of BMP-2 therefore corresponds to an imprint (groove) of a left-handed helix i. e. to an anti-helix or anthelix. The possible endogenous ligands and functions of these structures are unknown. These results demonstrate that full scale 3D molecular models of proteins can lead to new perceptions in understanding the interactions between ligands and proteins by macroscopic viewing and in-hand fitting of the molecules without the aid of a computer. Molekulares Modellieren des knochenmorphogenetischen Proteins-2 (BMP-2) mit Hilfe des 3D-Rapid Prototyping Knochenmorphogenetische Proteine (BMP) spielen eine entscheidende Rolle in der Entwicklung des Knochens und der Osteogenese. In der Vergangenheit waren sie als Stimulanzien des Knochenwachstums Gegenstand zahlreicher Forschungsvorhaben und klinischer Studien. Kürzlich wurde BMP-2 chemisch auf Implantat-Oberflächen immobilisiert, was bei Schafen zu verstärktem Knochenwachstum und beschleunigter Integration führte. Obwohl die 3D-Struktur von BMP-2 bekannt ist, war die Topographie seiner Oberfläche bisher nicht Thema einer detaillierten Analyse. Wir haben daher damit begonnen, die Technik des 3D-Rapid Protoyping als neue Methode zur Gewinnung topographischer Informationen über die Struktur-Funktions-Beziehung von Proteinen zu implementieren (Laub et al., 2001, FASEB J. 15, A543). Das 3D-Rapid Protoyping erlaubt die Konstruktion exakter drei-dimensionaler Modelle von Proteinen, basierend auf deren Röntgenstrukturdaten. Damit erzeugten wir ein maßstabsgetreues 3D-Abbild von BMP-2 mit den Maßen 140 × 70 × 50 mm, was einer Vergrößerung von 20 × 106 entspricht (Maßstab 1 nm = 2 cm). BMP-2 stellt sich als gedrehtes bananen-förmiges Molekül mit einer konvexen und einer konkaven Seite dar und besitzt an den Enden zwei hornähnliche Vorsprünge, die gegeneinander um 180°C (Längsachse) verdreht sind. Im Zentrum der konvexen Seite befindet sich eine ca. 1 nm tiefe kraterähnliche Vertiefung mit einem Durchmesser von ca. 1.8 nm. Die konkave Seite ist durch eine 6–7 nm lange, 0.8–1.6 nm breite und ca. 0.8 nm tiefe helikale Furche gekennzeichnet, in die eine linksgängige Helix mit einer Ganghöhe von 8–9 nm und einem helikalen Radius von 0.35–0.45 nm eingepasst werden kann. Die konkave Seite des BMP-2 entspricht daher dem Abdruck (Furche) einer linksgängigen Helix d. h. einer Anti-Helix oder Anthelix. Mögliche endogene Liganden und Funktionen dieser Struktur sind unbekannt. Diese Ergebnisse zeigen, dass 3D-Modelle von Proteinen durch makroskopisches Betrachten und Anpassen von Molekülen mit der Hand ohne Zuhilfenahme eines Computers zu neuen Erkenntnissen über die Interaktion zwischen Liganden und Proteinen führen können.