Untitled

Abstract

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 ZUSCHRIFTEN

Possible structures for the lamellar–isotropic (Lam‐I) and lamellar–nematic (Lam‐N) liquid crystalline phases

“…R5OCH 2 C*H(CH 3 ) O(CH 2 ) 11 C 8 F 17 ] can exhibit novel lamellar liquid crystalline phases, viz. lamellar isotropic (Lam-I), lamellar-nematic (Lam-N), and lamellar smectic A (Lam-A) phases [2][3][4][5][6][7], which are described below. Compound 1 (figure 1), which we refer to as 'mpp88,' exhibits all three of these lamellar phases (many materials exhibit only some of these phases) and moreover is designed to have low transition temperatures and a broad Lam-N region.…”

Liquid Crystals with Complex Superstructures

“…[4] More recently the formation of bicontinuous networks and spherelike aggregates was found to lead to new cubic and noncubic mesophase structures. [5][6][7] Based on the concept of competitive polyphilicity, elaborated in our laboratories, [8,9] it now seems possible to further increase the complexity of these self-organized fluid systems. This concept was successfully applied first to rodlike bolaamphiphiles with nonpolar lateral chains (see Figure 1), which form honeycomb-like arrays of cylinders and a series of novel layer structures.…”

Two‐ and Three‐Dimensional Liquid‐Crystal Phases from Axial Bundles of Rodlike Polyphiles: Segmented Cylinders, Crossed Columns, and Ribbons between Sheets

“…As typically observed for T-shaped amphiphiles with large lateral substituents, in lamellar (Lam) phases the rodlike units are parallel to the layer plane. [3,10] As shown by the persistence of the (001) reflection through the P6/mmm-Cmmm-Lam sequence (Figure 2 g), this periodicity is retained, confirming that the Lam phase has 2D long-range order (correlated layer phase, Lam Sm /p2mm). [15] At the Cmmm-Lam Sm transition the R F -rich columns are retained but change from undulated to straight.…”

“…Some are of unprecedented complexity, with tiles of several different shapes and "colors". [8,9] However, increasing the sidechain volume leads to lamellar phases (Figure 1 c) [10] and, by introducing branches, to inversion of the honeycombs, with the column core now inhabited by bundles of aromatic rods coaxial with the columns (Figure 1 d). [11,12] Herein we report a new type of bolaamphiphile (1, Scheme 1) having a lateral chain with two incompatible branches, a semiperfluorinated (R F ) and a carbosilane one (R Si ).…”

“…The colors of the fans (Figure 2 c, middle) reveal the orientation of the slow axis as tangential rather than Figure 1. Sequence of LC phases formed by rodlike bolaamphiphiles with incompatible lateral and terminal groups, upon increasing the size of the lateral chain(s): a, b) polygonal cylinder phases (rods normal to column); [3] c) lamellar phases (rods in plane of layer); [10] and d) axial-bundle phases (bundles of rods parallel to columns). [11,12] Molecules displaying these phases are sketched above: gray aromatic core, blue glycerol, green side chain.…”