A new type of square columnar liquid crystalline phases formed by facial amphiphilic triblock molecules

A series of three novel liquid crystalline amphiphilic molecules is reported which are composed of three incompatible molecular parts, a rigid terphenyl core, two lipophilic decyloxy chains in the terminal 4- and 4' '-positions, and a polar group in the lateral 2'-position. The polar group comprises a polyether chain, an amide group, and a polyhydroxyalkyl end group (1-acylamino-1-deoxy-d-sorbitol derivatives). The self-organization of these compounds was studied by polarized light microscopy, differential scanning calorimetry, and different X-ray diffraction techniques. These investigations confirm a novel liquid crystalline phase with a square 2D-lattice (square columnar mesophase, plane group p4mm). This structure is built up by a set of three distinct columns, namely columns containing the polar lateral groups, columns incorporating the alkyl chains, and ribbons of the rodlike terphenyl units. The calamitic cores form walls bounding square-shaped channels occupied by the microsegregated polar lateral chains. The lipophilic columns containing alkyl chains are at the corners interconnecting the aromatic rods end-to-end.     

Liquid crystalline bolaamphiphiles with semiperfluorinated lateral chains: competition between layerlike and honeycomb-like organization

Novel bolaamphiphilic triblockmolecules consisting of a rigid biphenyl unit, with a polar 2,3-dihydroxypropyloxy group and a phenolic OH group at opposite ends, as well as a semiperfluorinated chain in a lateral position have been synthesized via palladium catalyzed cross coupling reactions as the key steps. The thermotropic liquid crystalline behavior of these compounds was investigated by polarized light microscopy, DSC and X-ray scattering, and the influence of the length of the lateral chain on the mesomorphic properties was studied. The compound with the shortest chain as well as the long chain derivatives form lamellar mesophases composed of segregated layers of the bolaamphiphilic moieties and sublayers comprising the fluid lateral chains. The layers within the lamellar phases of the short chain compound adopt a positional correlation, leading to a 2D lattice (Col(r)/p2mm), whereas the layers of the lamellar phases of the long chain derivatives are noncorrelated (Lam). Compounds with a medium chain length organize into columnar phases, where the nonpolar lateral chains segregate into columns, which are embedded in networks of regular (Col(h)) or stretched (Col(r)/c2mm) hexagonal cylinder shells consisting of the bolaamphiphilic units. In total, an unusual phase sequence was found, where, with respect to the chain length, columnar mesophases occur between two mesophases with layer organization.     

Influence of flexible spacers on liquid-crystalline self-assembly of T-shaped bolaamphiphiles

T-shaped bolaamphiphiles composed of a biphenyl rigid core, a semiperfluorinated lateral chain, two polar 1,2-diol groups in the terminal positions and flexible alkyl spacers connecting the polar groups with the biphenyl core have been synthesized and investigated by polarizing microscopy, DSC and X-ray scattering. The influence of spacer length and position of the spacer on the self-assembly in liquid-crystalline phases was studied. A series of four different columnar phases (Col(hex)/p6mm, Col(rec)/p2gg, Col(squ)/p4gm and Col(squ)/p4mm), representing liquid-crystalline honeycomb structures composed of cylinders having hexagonal, pentagonal, and square cross section, were found on increasing the spacer length. It is also shown that introduction of aliphatic spacers in the backbone of the T-shaped bolaamphiphiles replaces the Col(rec)/c2mm phase made up of rhombic cylinders with the Col(squ)/p4mm phase composed of square cylinders. It also causes the 2d lattice of pentagonal cylinders to increase the symmetry from Col(rec)/p2gg to Col(squ)/p4gm. A temperature-dependent second-order phase transition between these two pentagonal cylinder structures was observed for the first time. Beside these effects on cylinder shape and phase symmetry the flexible spacer units also lead to reduced phase transition temperatures and allow adjustment of cylinder side length to envelop a wider range of side-chain sizes. Electron density maps suggest that this may involve sacrificing some of the hydrogen bonds.     

Highly Ordered Columnar Structures from Hexa-peri-hexabenzocoronenes—Synthesis,X-ray Diffraction,and Solid-State Heteronuclear Multiple-Quantum NMR Investigations

Improved long-range ordering in the columnar mesophase of hexa(para-n-dodecylphenyl)hexabenzocoronene 1 has been achieved by inserting phenyl rings between the extended aromatic core of hexabenzocoronene and the alkyl side chains, which are needed to form liquid crystalline phases. The long-range hexagonal order of the columns is demonstrated by X-ray scattering, while the improved packing of the aromatic cores within the columns and the molecular mobility is probed by a newly developed heteronuclear multiple-quantum MAS NMR technique.     

Alpha-helical-within-discotic columnar structures of a complex between poly(ethylene oxide)-block-poly(l-lysine) and a hexa-peri-hexabenzocoronene

Poly(ethylene oxide)-block-poly(l-lysine) (PEO-PLL) was complexed with an amphiphilic hexa-peri-hexabenzocoronene (HBC). This produced a thermotropic liquid crystalline material (PEO-PLL-HBC), which was investigated by FTIR spectroscopy and differential scanning calorimetry as well as by wide- and small-angle X-ray scattering. It was found that the poly(l-lysine) blocks form an alpha-helical secondary structure. Each helix is surrounded symmetrically by six discotic columns of HBC, which gives an alpha-helical-within-discotic column structural entity. The dense packing of these entities produces hexagonal sublattices (formed by the columns) in the frame of a two-dimensional hexagonal lattice (formed by the helices). An order-order transition from a columnar structure Col1 to Col2 was found at 54 degrees C. The unit cell constants are 5.75 nm (Col1) and 6.60 nm (Col2). The larger unit cell size of Col2 was explained by a higher intracolumnar order of the latter in which the packing distance of the disklike HBC cores is well-defined (0.353 nm). PEO-PLL-HBC combines essential features of liquid crystals with a basic structural element of proteins into a single material.     

Synthesis and Mesophase Behavior of Phenylthiophene Based Amphiphilic Molecules

Novel amphiphilic molecules consisting of a rigid 2‐phenylthiophene core, with a polar flexible tri(oxylethylene) moiety attached to the phenyl ring and one or two alkyl chains attached to the thiophene ring at the other side have been synthesized by using Ni(II) and Pd(0) catalyzed coupling reaction as key steps. The tri(oxylethylene) moieties were terminated with hydroxyl group, sodium carboxylate group and lithium carboxylate group respectively. The thermotropic and solvent induced liquid crystalline behavior of these substances was investigated by polarized optical microscopy, differential scanning calorimetry and X‐ray diffraction. Thereby the influence of the terminal groups attached to the tri(oxylethylene) moities as well as the influence of the length and the number of the alkyl chains on the mesophase behavior were investigated. The single alkyl chain Na‐carboxylate termianted derivatives show smectic A phases, double alkyl chain Na‐carboxylate terminated derivatives show a thermo tropic hexagonal columnar mesophase, while columnar mesophases are found in both single and double alkyl chain Li‐carbonate terminated derivatives. The model for molecular organization in the hexagonal columnar mesophase is established.     

Calamitic bolaamphiphiles with (semi)perfluorinated lateral chains: polyphilic block molecules with new liquid crystalline phase structures

Novel bolaamphiphiles consisting of a rigid biphenyl unit, two terminal polar 1,2-diol units and laterally attached (semi)perfluorinated chains have been synthesized via palladium-catalyzed cross coupling reactions as the key step. The thermotropic liquid crystalline behavior of these compounds was investigated by polarized light optical microscopy, DSC, and X-ray scattering, and the influences of the length, number, structure, and position of the lateral chain on the mesomorphic properties were studied. A wide variety of unique liquid crystalline phases were found upon elongation of the lateral semiperfluorinated chains. For short- and medium-chain length a series of columnar phases were observed, and upon further elongation of the lateral chain a series of novel mesophases with layer structures were found. In the columnar phases, the nonpolar lateral chains segregate into columns, which are embedded in honeycomb-like networks of cylinders consisting of the biphenyl units. Strings of hydrogen-bonding networks of the diol groups provide cohesive forces, which maintain the overall structure. Changing the length of the lateral chains influences the diameter of the columns and thus determines the number of biphenyl units which are required to surround these columns. The number of these units [four (c2mm, p4mm), five (p2gg), six (p6mm), eight (c2mm) or 10 (p2gg)] defines the shape of the cylinders as well as the lattice type of the columnar phase. It is proposed that the columnar phases with a p2gg lattice result from the regular organization of pairs of cylinders which have a pentagonal cross sectional shape. In the mesophases with layer structure the aromatic rodlike cores are arranged parallel to the layer planes, and the onset of orientational and positional ordering of the biphenyl segments leads to a sequence of subtypes for these lamellar phases (Lam(Iso)-Lam(N)-Lam(X)).     

Distinct columnar and lamellar liquid crystalline phases formed by new bolaamphiphiles with linear and branched lateral hydrocarbon chains

A universal building block for the convergent synthesis of a wide variety of different T-shaped ternary amphiphiles was developed and used for the synthesis of a series of new liquid-crystalline materials composed of a rigid biphenyl core with polar glycerol groups at both ends and linear or branched alkyl chains in a lateral position. In addition, compounds with bulky achiral (2,4,6-trimethylphenoxy, adamantane-1-carboxylate, benzoate) or chiral (menthyl or cholesteryl) substituents attached to the end of the lateral alkyl chain were also investigated. In all cases the lateral chains were connected to the aromatic core by an ether linkage. The effect of the ether linking unit on mesophase stability and mesophase type is discussed with respect to conformational effects. The liquid-crystalline phases were investigated by polarizing microscopy, calorimetry, and X-ray diffraction of surface aligned samples. Upon enlarging the lateral chains a series of different polygonal cylinder phases was observed, which were replaced by lamellar phases and a non-cylinder hexagonal columnar phase by further increasing the size of these substituents. Remarkably, only pentagonal, hexagonal, and giant hexagonal cylinder phases could be observed, whereas mesophases composed of cylinders with a smaller number of sides are missing. No distinct chirality effects were observed for the menthyl- and cholesteryl-substituted compounds. However, the rodlike shape of the polycyclic cholesteryl core leads to a unique phase structure combining an organization of the alicyclic cholesteryl cores perpendicular to the layer planes and the aromatic biphenyl cores parallel to the layer planes.     

Synthesis and mesophase behaviour of rigid rod‐like phenylthiophene‐based amphiphilic diol derivatives

Novel amphiphilic block molecules consisting of a rigid 2‐phenylthiophene or 5‐phenylbithienyl core, with a polar glycerol group attached to the phenyl ring and one or two alkyl chains attached to the thiophene ring on the other side, have been synthesised by using Ni(0) and Pd(0) catalyzed coupling reactions as key steps. The thermotropic and solvent‐induced liquid crystalline behaviour of these compounds was investigated by polarising optical microscopy and X‐ray diffraction. The influence of the length, number and position of the alkyl chains, and the length of the rigid core, on their mesophase behaviour was investigated. Compounds with one alkyl chain in the terminal 5‐position on the thiophene ring form only smectic A phases, compounds with two adjacent alkyl chains attached in the 4‐ and 5‐positions of the thiophene ring exhibit thermotropic columnar mesophases, and those with two long alkyl chains attached to the 3‐ and 5‐positions form columnar LC phases only in the presence of water. Another compound containing the longer 5‐phenylbithienyl core unit and two alkyl chains attached in lateral positions to each of the thiophene rings is not mesogenic.     

Axial-bundle phases--new modes of 2D, 3D, and helical columnar self-assembly in liquid crystalline phases of bolaamphiphiles with swallow tail lateral chains

Two series of polyphilic molecules composed of a rigid and linear p-terphenyl core, terminated at both ends with polar glycerol groups capable of hydrogen bonding, and two branched swallow tail-type lateral chains, composed of a fluorinated and a nonfluorinated branch or two fluorinated branches, were synthesized and investigated by differential scanning calorimetry, polarizing microscopy, and X-ray diffraction (XRD) with respect to their self-assembly in thermotropic liquid crystalline (LC) phases. Hexagonal columnar phases were formed by all molecules, at least at the highest temperature. In these phases the columns are composed of a core of aromatic rods and an aliphatic shell. The aromatic rods form bundles which are rotationally averaged and lie parallel to the column long axis. This unique organization is proven by different optical and XRD methods. The aromatic and glycerol groups inside the rod bundles are segregated into alternating segments. Depending on temperature and molecular structure, long-range intercolumnar correlation of this periodicity could take place, leading to a 3D-ordered LC phase with rhombohedral R ?3m symmetry. The bundles are embedded in the matrix of the lateral chains, which is divided into fluoroalkyl- and aliphatic-rich regions. In the 2D columnar phase the fluorinated regions take the form of either straight columns running along the edges of the hexagonal Voronoi cells or, for compounds with a higher degree of fluorination, fuse to a hexagonal honeycomb enclosing the aromatic cores. In the R ?3m phase the fluorine-rich chains are preferentially found along right- and left-handed helices wound around the 3(1) screw axes between the main aromatic columns.     

具有不同柱状结构的苯并菲盘状液晶化合物的合成及自组装

合成了3种含有不同长度烷基链的苯并菲盘状液晶化合物; 通过1H NMR 和 MALDI-TOF MS对其结构进行了表征; 利用差示扫描量热法(DSC)、热台偏光显微镜(POM)和小角X射线散射实验(SAXS)对3种液晶化合物的自组装行为进行了研究. 结果表明, 烷基链的长度对苯并菲盘状液晶化合物自组装结构的影响显著. 柔性链为辛基的苯并菲盘状液晶化合物自组装成六方柱状液晶相; 柔性链为十二烷基的化合物自组装成倾斜柱状液晶相; 而柔性链为十六烷基的化合物则未形成液晶相.     

Interplay between H‐Bonding and Alkyl‐Chain Ordering in Self‐Assembly of Monodendritic L‐Alanine Derivatives

This paper reports on the synthesis and self‐organizing properties of monodendrons consisting of L ‐alanine at the focal point and alkyl chains with different length at the periphery. The structures of thin films and monolayers are studied by temperature‐resolved grazing‐incidence X‐ray diffraction and scanning force microscopy. The interplay between H‐bonding and ordering of the alkyl chains results in a rich temperature‐dependent phase behavior. The monodendrons form H‐bonded stabilized clusters with the number of molecules depending on the length of the aliphatic chains and temperature. The clusters play the role of constitutive units in the subsequent self‐assembly. Short alkyl chains allow the material to form thermodynamically stable crystalline phases. The molecules with longer side groups exhibit additional transitions from the crystalline phase to thermotropic columnar hexagonal or columnar rectangular liquid‐crystalline phases. In monolayers deposited on highly ordered pyrolytic graphite, the materials show ordering similar to thin films. However, for the compound bearing hexadecyl chains the affinity of the alkyl groups to graphite dominates the self‐assembly and thereby allows epitaxial growth of a 2D lattice with flat‐on oriented molecules.     

Mesomorphic and dynamic properties of discotic alkanoyloxybenzene dimers as studied by X-ray and NMR: The effect of spacer length

The preparation and mesomorphic properties of four members of the homologous series of dimers, alkandioic acid bis\[pentakis( n -heptanoyloxy)phenyl] esters \[(C6 H13 COO)5 C6 OC(O)(CH2 )(n-2)/2]2 with n= 6, 8, 12 and 14, are reported. They are henceforth referred to as T n. Between -100 C and the isotropic liquid (I) the four compounds exhibit, with increasing temperature, the phase sequence Cr P I, where Cr is a solid and P is an intermediate phase which is crystalline for T6 and T8, and columnar discotic for T12 and T14. The mesophases of T12 and T14 are completely miscible with that of the corresponding monomer, hexaheptanoyloxybenzene (BHA7) and thus are identified as of type Col rd. This assignment is confirmed by X-ray measurements which also provide the lattice parameters for the two-dimensional columnar array. Deuterium and carbon-13 NMR measurements indicate that the side chains in the P(Cr) phases of T6 and T8 are dynamically disordered, while the benzene core is rigid. In the P(Col) mesophases of T12 and T14, the side chains are also disordered, but in addition the benzene cores undergo high amplitude planar librations. Analysis of the carbon-13 spectra of the carboxyl groups in the latter compounds shows a distribution of librational amplitudes around a mean value of about one rad with a variance of 0.14 rad2. The structure of the mesophases can be visualized as columns consisting of stacked monomeric units. The monomers are linked via spacers to their counterparts in neighbouring columns. The stacking level of the monomeric units in neighbouring columns is not correlated. Some pairs are stacked at the same level, resulting in loose spacers and high librational amplitudes, while other pairs are stacked at different levels with a corresponding tightening of the spacers and reduced librational amplitudes.     

Plank‐Shaped Column‐Forming Mesogens with Substituents on One Side Only

Prolonged glyoxylation of pyrenyl‐1‐glyoxylic acid ethyl ester leads to a mixture of isomers with polar pyrenylene‐1,8‐diglyoxylic acid as the main product, whereas the centrosymmetric 1,6‐isomer is obtained in good yield from the corresponding dibromopyrene. Perkin condensations followed by Pd‐catalyzed cyclizations lead to isomeric dinaphthopyrene‐tetracarboxdiimides that self‐assemble into columnar liquid crystals of hexagonal and rectangular symmetry, of which the rectangular mesophases have unusually elongated unit cells. The cisoid diimides with both alkylimide substituents on the same side of the oblong arene system show a much greater tendency to self‐assemble into fluid stacks of disks than their centrosymmetric isomers. With racemically branched alkyl substituents, uniform vertical surface alignment of the columns in the high‐temperature hexagonal mesophase is resilient to cycling through the lower‐temperature rectangular and crystalline phases.     

Triblock Polyphiles through Click Chemistry: Self‐Assembled Thermotropic Cubic Phases Formed by Micellar and Monolayer Vesicular Aggregates

Three series of triblock polyphiles consisting of a rigid 4‐phenyl‐1,2,3‐triazole or 1,4‐diphenyl‐1,2,3‐triazole core with three lipophilic and flexible alkoxyl chains at one end and a polar glycerol group at the opposite end were synthesized by copper‐catalyzed azide–alkyne click reactions. Their mesophase behavior was studied by polarizing optical microscopy, differential scanning calorimetry, and XRD. Depending on alkyl chain length and core length, a transition from hexagonal columnar to ${{\it Pm}\bar 3n}$ ‐type cubic phases was observed. In the cubic phases, the molecules are organized as spherical objects. Remarkably, compounds with a longer core unit have a higher tendency to form these cubic phases, and their stability is strongly enhanced over those of the compounds with a shorter core, despite longer cores having a smaller cone angle and therefore being expected to disfavor the formation of spherical objects. There is a large difference in the number of molecules involved in the spherical aggregates formed by compounds with long and short cores. Whereas the aggregates in the cubic phases of the compounds with short rod units are small and could be regarded as micellar, the long‐core compounds form much larger aggregates which are regarded as a kind of monolayer vesicular aggregate.     

X-Shaped polyphilics: liquid crystal honeycombs with single-molecule walls

X-Shaped ternary five-block molecules, composed of a rigid p-terphenyl core, two terminal glycerol groups and two flexible n-alkyl or semiperfluorinated chains fixed laterally to opposite sides of the terphenyl moiety, form liquid crystalline phases built up of honeycomb-like arrays of polygonal cylinders, where the rod-like aromatic cores form cylinder walls with a thickness equal to the width of a single molecule.     

Correlated layer structures: a novel type of liquid crystalline phase with 2D-lattice

A novel liquid crystalline quaternary five-block molecule is reported which is composed of four incompatible molecular parts, a rigid biphenyl core, two polar 2,3-dihydroxypropoxy groups in the terminal 4- and 4'-positions, and a branched semiperfluorinated chain in the lateral 3-position, consisting of a perfluorinated and a lipophilic hydrocarbon wing. The self-organization of this compound was studied by polarized light optical microscopy, differential scanning calorimetry, and X-ray diffraction of aligned samples. These investigations confirm a novel liquid crystalline phase with two-dimensional (2D) lattice (columnar mesophase), which results from the positional correlation of smectic layers. The layer structure results from the segregation of the bolaamphiphilic parts from the side chains. Within the aromatic sublayers the biphenyl cores are arranged parallel to the layer planes, and the hydrogen-bonding networks of the terminal diol groups are segregated from the biphenyl cores, forming separate columns. The correlation between adjacent layers is due to the (partial) segregation of the fluorinated and hydrogenated parts of the lateral chains in the nonpolar sublayers.     

Thermotropic liquid crystalline behaviour of piperazinium and homopiperazinium alkylsulphates

A series of 1,4-piperazinium di- n -alkyl sulphates was synthesized and compared with an analogous series of 1,5-homopiperazinium di- n -alkyl sulphates. Their thermotropic liquid crystalline behaviour was studied by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. For the piperazinium salts, two ordered smectic phases were established, in which the lateral packing of the molecules within the layers is rectangular or tetragonal. Both phases are characterized by an alternate periodic packing of the positive and negative ionic groups in the polar sublayer, while the lipophilic sublayers of the alkyl chains are in a disordered conformation. Substitution of the piperazinium by the less symmetrical homopiperazinium group disfavours organization within the smectic layer and as a result smectic A phases were obtained.     

Amphiphilic taper-shaped oligomer exhibiting a monolayer smectic A to columnar phase transition

We prepared two series of liquid-crystalline oligomers composed of phenylpyrimidine based mesogenic cores, alkyl spacers and semiperfluorinated alkyl chains in one series and only alkyl chains in the second series. Their physical properties were investigated using optical microscopy, differential scanning calorimetry and X-ray diffraction measurements. The oligomers possessing a semiperfluorinated alkyl chain show a phase sequence of SmC–SmA–Col when the number of phenylpyrimidine moieties was increased. The compound possessing three phenylpyrimidine cores was found to exhibit monolayer SmA and Col phases. On the other hand, the oligomer composed of an alkyl chain and three phenylpyrimidine cores showed only a nematic phase. We discuss effects of the shape amphiphilicity and the hydrocarbon–fluorocarbon amphiphilicity on phase transition behaviour of the amphiphilic oligomers.     

Discotic liquid crystalline poly(propylene imine) dendrimers based on triphenylene

The design, synthesis, and mesomorphic properties of a new series of homodendrimers consisting of the commercially available poly(propylene imine) (PPI) dendrimers (G = 1-5), PPI-(NH(2))(n)() (n = 4, 8, 16, 32, 64), functionalized with a discotic triphenylene moiety are reported. The liquid crystalline behavior was investigated by means of differential scanning calorimetry (DSC), polarizing-light optical microscopy (POM), and X-ray diffractometry (XRD). All of the homodendrimers showed mesomorphic properties, with the second to fifth generations giving a hexagonal columnar mesophase (Col(h)) and the first generation a rectangular columnar mesophase (Col(r)). The X-ray study reveals that these mesophases show a highly ordered structure with segregation of triphenylenes and dendrimers into separate columns and a regular stacking distance inside the triphenylene columns. GPC analysis showed that the dendrimers had good monodispersity and MALDI-TOF studies of the first three generations gave good evidence that all of the terminal amino groups of the dendrimers were functionalized with a discotic unit.