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)).

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T-shaped polyphilic triblock molecules, consisting of a rodlike p-terphenyl unit, a hydrophilic and flexible laterally attached oligo(oxyethylene) chain terminated by an 1-acylamino-1-deoxy-D-sorbitol unit, and two end-attached lipophilic alkyl chains, have been synthesized by palladium-catalyzed cross-coupling reactions as the key steps. The thermotropic liquid crystalline behavior of these compounds was investigated by polarized light microscopy, differential scanning calorimetry (DSC), and X-ray scattering. We investigated the mode of self-organization as a function of the length and position of the lateral polar chain and the length of the terminal alkyl chains. Depending on the size of the polar and lipophilic segments, a series of unusual liquid crystalline phases was detected. In three of these phases, the space is divided into three distinct periodic subspaces. In addition to a hexagonal channeled layer phase (ChL(hex)) consisting of layers that are penetrated by polar columns, there are also two honeycomb-like network structures formed by square (Col(squ)/p4mm) or pentagonal cylinders (Col(squ)/p4gm). The cylinder walls consist of the terphenyl units fused by columns of alkyl chains, and the interior contains the polar side chains. In addition, a hexagonal columnar phase was observed in which the polar columns are organized in a continuum of terphenyls and alkyl chains with an organization of the terphenyl cores tangentially around the columns with the long axis perpendicular to the columns. For one compound, a reversal of birefringence was observed, which is explained by a reorientation of the terphenyl cores. The addition of protic solvents induces lamellar phases.

Investigation of the driving forces of molecular selforganization is one of the most exciting and most rapidly growing areas of chemical research. In this respect, ordered structures with liquid-crystalline (LC) properties are of special interest, because they are reversibly formed under thermodynamic equilibrium conditions and combine order and mobility on molecular, supramolecular, and macroscopic levels. The mobility enables them to respond to different external stimuli by changing their configuration, which in turn determines their importance in biological systems and technical applications. [1] In conventional LC materials rod-or disklike anisometric rigid units, which provide long-range orientational order, are connected to flexible alkyl chains, which are largely responsible for positional order and mobility. This design principle leads to the well-known nematic, smectic, and columnar LC phases. [2] A characteristic feature of such LC materials is a molecular topology in which rigid cores and flexible chains are connected in such a manner that the parallel organization of the rigid segments and the segregation of the incompatible molecular parts enhance each other.Exciting new mesophase morphologies can be realized if rodlike (calamitic) rigid units are combined with two incompatible subunits in a competitive and nonlinear manner. [3,4] Examples are bolaamphiphilic biphenyl derivatives carrying a long lateral alkyl chain. [4] In such bolaamphiphiles, the strongest attractive forces (hydrogen bonding) act at the two termini of a rigid calamitic core. The lateral alkyl chains represent a third group of units that are incompatible with both the polar terminal diol groups [5] and the rigid biphenyl cores. As a consequence, each of these units segregates into its own subspace, and a series of unusual columnar mesophases results. They are built up by networks of cylinders, formed by ribbons of the biphenyl cores which are held together by ribbons of hydrogen-bonding networks (see Figure 1). The COMMUNICATIONS

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.

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Novel amphiphilic diols with semifluorinated alkyl chains have been synthesized. These are 1-benzoylaminopropane-2,3-diols carrying one, two, or three semiperfluorinated chains at the aromatic core, as well as a 2-benzoylaminopropane-1,3-diol and a 2-benzoylaminoethanol with two semiperfluorinated chains. Their thermotropic liquid crystalline properties were investigated by means of polarizing microscopy, differential scanning calorimetry, and X-ray diffraction. In comparison with the related hydrocarbon compounds, the semifluorinated analogues have significantly more stable mesophases. Because of the larger cross-sectional area of the perfluorinated segments, not only the three-chain compounds but also most two-chain compounds have reverse discontinuous (micellar) cubic mesophases (CubI2). Additionally, phase diagrams of binary systems of a single-chain amphiphile with the two-and three-chain amphiphiles have been investigated. Hexagonal columnar (Colh2) and bicontinuous cubic phases (CubV2) were induced in such systems. Remarkably, the CubV2 phases occur only above a distinct temperature, whereas at lower temperature a direct transition between the lamellar phase and the columnar phase takes place. This leads to a reentrant behavior of the smectic A phases and columnar phases in certain concentration ranges.

Novel lamellar mesophases which are quite distinct from conventional smectic mesophases were obtained with a bolaamphiphilic triblock molecule composed of a rigid biphenyl core, two polar 2,3-dihydroxypropoxy groups in the terminal 4- and 4'-positions, and a semiperfluorinated chain [O(CH2)6C10F21] in the lateral 3-position. The competitive combination of microsegregation and rigidity in this molecule leads to layer structures in which the bolaamphiphilic cores segregate from the lateral chains into distinct sublayers. In these sublayers the biphenyl cores are aligned parallel to the layer planes. Decreasing the temperature leads to a subsequent inset of orientational and positional order of the biphenyl unit, which leads to a transition from an uniaxial SmA phase to a biaxial SmAb phase and finally to a mesophase with an additional periodicity within the aromatic sublayers. Here, microsegregation occurs on two distinct levels: The segregation of the nonpolar chains from the aromatic cores leads to the "bulk" layer structure and segregation of polar and aromatic subunits within the aromatic sublayers gives rise to an additional periodicity within the aromatic sublayers. These phases can be regarded as smectic phases built up by quasi-2D layers with nematic, respectively SmA-like order, separated by isotropic layers of the lateral chains.