Fluorophobic Effect Induces the Self-Assembly of Semifluorinated Tapered Monodendrons Containing Crown Ethers into Supramolecular Columnar Dendrimers Which Exhibit a Homeotropic Hexagonal Columnar Liquid Crystalline Phase

The rational design, synthesis, and characterization of the building blocks obtained by the esterification of the first generation of tapered monodendrons 3,4,5-tris(p-dodecan-1-yloxy)benzoic acid (12-AG) and 3,4,5-tris[p-(n-dodecan-1-yloxy)benzyloxy]benzoic acid (12-ABG) containing semifluorinated dodecyl groups [i.e., 12Fn-AG-15C5 (n = 0, 4, 6, 8), 12Fn-AG-B15C5, 12Fn-ABG-15C5, and 12Fn-ABG-B15C5 (n = 0 and 8) where n following the letter F represents the number of outer perfluorinated methylenic units of the dodecyl group] with 4‘-hydroxymethyl(benzo-15-crown-5) (B15C5) and 1-hydroxymethyl(15-crown-5) (15C5) are described. All building blocks self-assemble into supramolecular cylindrical or rod-like dendrimers via ion-mediated complexation processes. These rod-like supermolecules form a thermotropic hexagonal columnar (Φh) liquid crystalline (LC) phase. The fluorination of the dodecyl groups of these tapered building blocks enhances dramatically their self-assembly ability. The building blocks based on n = 6 and 8 self-assemble into supramolecular columns solely via the fluorophobic effect. Direct structural characterization of the supramolecular columns obtained via these two molecular recognition processes by a combination of techniques consisting of differential scanning calorimetry, X-ray diffraction, and thermal optical polarized microscopy, and of the columns obtained solely via the fluorophobic effect allowed the construction of molecular models for the supramolecular columns obtained via these two organizing forces. An increase in the column diameter with increasing n and with the complexation of metal salts (i.e., alkali metal trifluoromethanesulfonates) accounts for a structural model in which the uncomplexed and complexed crown ethers are placed side-by-side in the center of the column with the melted tapered side groups radiating toward its periphery. The perfluorinated segments of the building blocks are microsegregated from the perhydrogenated and aromatic segments of the column. The supramolecular columns obtained from building blocks with n = 8 align homeotropically in the Φh LC phase on untreated glass slides, i.e., form single crystal liquid crystals in which the long axes of their columns are perpendicular to the glass surface. Both the self-assembly of supramolecular columns induced solely by the fluorophobic effect and the homeotropic alignment of these columns in their Φh LC phase open extremely interesting new synthetic and technologic opportunities in the area of self-assembly of well-defined supramolecular architectures obtained from monodendrons and other building blocks

Structure of Liquid Crystalline Aerosol-OT and Its Alkylammonium Salts

Aerosol-OT is a widely used anionic surfactant, and its lyotropic properties have been studied extensively. However, neat AOT is itself liquid crystalline. We carried out an X-ray study of neat AOT sodium salt, as well as of AOT -n-decyl-, n-dodecyl-, n-tetradecyl-, and n-hexadecylammonium salts. We confirm an earlier report that pure AOT forms a hexagonal columnar phase but propose a different packing model. This involves a relatively highly ordered structure with each column cross-section containing three tessellated molecules in the plane normal to the column axis. The structure is trigonal locally but hexagonal over the long-range. This mode of assembly is supported by electron density reconstruction and molecular modeling. At subambient temperatures, the AOT−alkylammonium complexes Cn−AOT, with n = 10−16, also display a hexagonal columnar phase, but this is more disordered, and each column cross-section contains only two ion pairs. Unusually, molar enthalpy and entropy of the columnar-isotropic transition in Cn−AOT salts decrease with increasing n. This is attributed to a disproportionally high conformational disorder of the radial chains in the columnar phase, which is required for efficient space filling

Skeletal Cubic, Lamellar, and Ribbon Phases of Bundled Thermo­tropic Bolapolyphiles

A series of T-shaped polyphilic molecules composed of a rigid linear biphenyl core with a polar glycerol group at each end and one swallow-tail semi­perfluorinated lateral chain were synthesized and their thermo­tropic liquid crystalline (LC) phases were investigated by X-ray diffraction, calorimetry, and microscopy. The compounds have a long alkyl spacer between the aromatic core and the fluorinated C_<i>n</i>F_2<i>n</i>+1 ends, where <i>n</i> = 4, 6, 8, and 10. Upon melting, all compounds start with lamellar LC phases, followed on heating by a rectangular columnar ribbon phase with <i>c</i>2<i>mm</i> symmetry. Unusually, a ribbon is a flat bundle of molecular cores highly aligned <i>parallel</i> to the ribbon axis. On further heating, for <i>n</i> = 8 and 10, this phase is succeeded by a bicontinuous cubic phase with <i>Ia</i>3̅<i>d</i> symmetry. This is a new variant of the “gyroid” phase, with axially oriented rod-like molecular cores forming the skeleton of the two infinite networks and junctions separated by exactly two molecular lengths. In this tricontinuous core–shell structure (aromatic–aliphatic–perfluoro­alkyl), the polar glycerol domains of appreciable size, contained within the skeleton, can be considered as micellar

Comparison of the A-T rich regions and the Bacillus subtilis RNA polymerase binding sites in phage ø29

By using a modification of the BAC spreading method for mounting the DNA for electron microscopy, partial denaturation maps of protein-free ø29 DNA and of ø29 DNA containing protein p3 were obtained. In ø29 P3-DNA1 the protein does not seem to influence the melting of the ends of the molecules. The comparison of the partial denaturation map and the B. subtilis RNA polymerase binding sites indicates that five of the seven early promoters (Al, A2, A3, B2 and C2) are located in A-T rich DNA regions whereas the other two early promoters (Bl and Cl) are located in less A-T rich sites.Peer reviewe

Synthesis and Structural Analysis of Two Constitutional Isomeric Libraries of AB₂-Based Monodendrons and Supramolecular Dendrimers

The synthesis and structural analysis of two constitutional isomeric libraries of self-assembling AB2 monodendrons based on 3,4- and 3,5-disubstituted benzyl ether internal repeat units containing four different first generation monodendrons, i.e., 3,4,5-tris(n-dodecan-1-yloxy)benzyl ether, 3,4-bis(n-dodecan-1-yloxy)benzyl ether, 3,4,5-tris[p-(n-dodecan-1-yloxy)benzyloxy]benzyl ether, and 3,4-bis[p-(n-dodecan-1-yloxy)benzyloxy]benzyl ether, on their periphery are described. Regardless of the repeat unit on their periphery, the first three or four generations of the 3,4-disubstituted series of monodendrons self-assemble into spherical supramolecular dendrimers that self-organize into a Pm3̄n 3-D cubic lattice while the same generations of the 3,5-disubstituted series of monodendrons self-assemble into cylindrical supramolecular dendrimers that self-organize into a p6mm hexagonal columnar 2-D lattice. The internal repeat unit of the monodendrons determines the shape of the supramolecular dendrimers. However, for a particular internal repeat unit, the architecture from its periphery determines the size of the monodendron, the number of monodendrons that self-assemble into a supramolecular dendrimer, the solid angle of the monodendron, and the dependence of the size of the supramolecular dendrimer on generation number. Since ultimately all monodendrons must reach the shape of a single sphere, the diameter of cylindrical and spherical supramolecular dendrimers constructed from these building blocks is limited to less than 100 Å. The library of 3,5-disubstituted monodendrons also provided the first five examples of supramolecular dendrimers that undergo reversible shape changes induced by temperature and functionality at their focal point. In addition, a spherical supramolecular dendrimer based on a 3,5-disubstituted repeat unit that self-assembles in an Im3̄m 3-D cubic lattice was discovered in the same library. The structural information generated by these two AB2 and the previously reported AB3 libraries of quasi-equivalent monodendrons provides building blocks that enable the construction of externally regulated functional supramolecular, macromolecular, and single-molecule-based nanosystems self-organizable in predictable lattices

2D and 3D Ordered Columnar Liquid Crystal Phases by Bundles of Bolaamphiphiles with Swallow-Tail Side Chains

2D and 3D Ordered Columnar Liquid Crystal Phases by Bundles of Bolaamphiphiles with Swallow-Tail Side Chain

Electro-Functional Octupolar π-Conjugated Columnar Liquid Crystals

A series of propeller-shaped π-conjugated molecules based on 2,4,6-tris(thiophene-2-yl)-1,3,5-triazines has been designed and synthesized to obtain ambipolar charge-transporting liquid-crystalline materials. The 3-fold electron-donating aromatic units are attached to the electron-accepting triazine core, which forms electro-functional octupolar π-conjugated structures. These octupolar molecules self-organize into one-dimensional columnar nanostructures and exhibit ambipolar carrier transport behavior, which has been revealed by time-of-flight measurements. In this approach, electron-donor and acceptor electro-active segments are assembled individually in each column to give one-dimensional nanostructured materials with precisely tuned electronic properties. Their desirable electronic structures responsible for both hole and electron conductions have also been examined by cyclic voltammetry and theoretical calculations. The present results provide a new guideline and versatile approach to the design of ambipolar conductive nanostructured liquid-crystalline materials

Electro-Functional Octupolar π-Conjugated Columnar Liquid Crystals

A series of propeller-shaped π-conjugated molecules based on 2,4,6-tris(thiophene-2-yl)-1,3,5-triazines has been designed and synthesized to obtain ambipolar charge-transporting liquid-crystalline materials. The 3-fold electron-donating aromatic units are attached to the electron-accepting triazine core, which forms electro-functional octupolar π-conjugated structures. These octupolar molecules self-organize into one-dimensional columnar nanostructures and exhibit ambipolar carrier transport behavior, which has been revealed by time-of-flight measurements. In this approach, electron-donor and acceptor electro-active segments are assembled individually in each column to give one-dimensional nanostructured materials with precisely tuned electronic properties. Their desirable electronic structures responsible for both hole and electron conductions have also been examined by cyclic voltammetry and theoretical calculations. The present results provide a new guideline and versatile approach to the design of ambipolar conductive nanostructured liquid-crystalline materials

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 R3̅m 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 R3̅m phase the fluorine-rich chains are preferentially found along right- and left-handed helices wound around the 31 screw axes between the main aromatic columns

Synthesis and Structural Analysis of Two Constitutional Isomeric Libraries of AB₂-Based Monodendrons and Supramolecular Dendrimers

The synthesis and structural analysis of two constitutional isomeric libraries of self-assembling AB2 monodendrons based on 3,4- and 3,5-disubstituted benzyl ether internal repeat units containing four different first generation monodendrons, i.e., 3,4,5-tris(n-dodecan-1-yloxy)benzyl ether, 3,4-bis(n-dodecan-1-yloxy)benzyl ether, 3,4,5-tris[p-(n-dodecan-1-yloxy)benzyloxy]benzyl ether, and 3,4-bis[p-(n-dodecan-1-yloxy)benzyloxy]benzyl ether, on their periphery are described. Regardless of the repeat unit on their periphery, the first three or four generations of the 3,4-disubstituted series of monodendrons self-assemble into spherical supramolecular dendrimers that self-organize into a Pm3̄n 3-D cubic lattice while the same generations of the 3,5-disubstituted series of monodendrons self-assemble into cylindrical supramolecular dendrimers that self-organize into a p6mm hexagonal columnar 2-D lattice. The internal repeat unit of the monodendrons determines the shape of the supramolecular dendrimers. However, for a particular internal repeat unit, the architecture from its periphery determines the size of the monodendron, the number of monodendrons that self-assemble into a supramolecular dendrimer, the solid angle of the monodendron, and the dependence of the size of the supramolecular dendrimer on generation number. Since ultimately all monodendrons must reach the shape of a single sphere, the diameter of cylindrical and spherical supramolecular dendrimers constructed from these building blocks is limited to less than 100 Å. The library of 3,5-disubstituted monodendrons also provided the first five examples of supramolecular dendrimers that undergo reversible shape changes induced by temperature and functionality at their focal point. In addition, a spherical supramolecular dendrimer based on a 3,5-disubstituted repeat unit that self-assembles in an Im3̄m 3-D cubic lattice was discovered in the same library. The structural information generated by these two AB2 and the previously reported AB3 libraries of quasi-equivalent monodendrons provides building blocks that enable the construction of externally regulated functional supramolecular, macromolecular, and single-molecule-based nanosystems self-organizable in predictable lattices