Influence of Flexible Spacers on Liquid-Crystalline Self-Assembly of T-Shaped Bolaamphiphiles

Cheng, Xiaohong,Liu, Feng,Zeng, Xiangbing,Ungar, Goran,Kain, Jens,Diele, Siegmar,Prehm, Marko,Tschierske, Carsten American Chemical Society 2011 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.133 No.20

<P>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<SUB>hex</SUB>/<I>p</I>6<I>mm</I>, Col<SUB>rec</SUB>/<I>p</I>2<I>gg</I>, Col<SUB>squ</SUB>/<I>p</I>4<I>gm</I> and Col<SUB>squ</SUB>/<I>p</I>4<I>mm</I>), 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<SUB>rec</SUB>/<I>c</I>2<I>mm</I> phase made up of rhombic cylinders with the Col<SUB>squ</SUB>/<I>p</I>4<I>mm</I> phase composed of square cylinders. It also causes the 2d lattice of pentagonal cylinders to increase the symmetry from Col<SUB>rec</SUB>/<I>p</I>2<I>gg</I> to Col<SUB>squ</SUB>/<I>p</I>4<I>gm</I>. 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.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2011/jacsat.2011.133.issue-20/ja200822z/production/images/medium/ja-2011-00822z_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja200822z'>ACS Electronic Supporting Info</A></P>

Simple Cubic Packing of Gold Nanoparticles through Rational Design of Their Dendrimeric Corona

Kanie, Kiyoshi,Matsubara, Masaki,Zeng, Xiangbing,Liu, Feng,Ungar, Goran,Nakamura, Hiroshi,Muramatsu, Atsushi American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.2

<P>The first simple-cubic liquid crystal was obtained by coating monodisperse Au nanoparticles (NPs) with a thick corona of amino-substituted organic dendrons. This unusual structure was determined by grazing-incidence diffraction and electron density reconstruction and explained by analyzing the radial density profile of the corona. Another novel structure is proposed for the phase preceding the cubic one: a hexagonal superlattice composed of alternating dense and sparse strings of Au NPs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-2/ja2095816/production/images/medium/ja-2011-095816_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja2095816'>ACS Electronic Supporting Info</A></P>

One-Step Synthesis and Self-Assembly of Metal Oxide Nanoparticles into 3D Superlattices

Pucci, Andrea,Willinger, Marc-Georg,Liu, Feng,Zeng, Xiangbing,Rebuttini, Valentina,Clavel, Guylhaine,Bai, Xue,Ungar, Goran,Pinna, Nicola American Chemical Society 2012 ACS NANO Vol.6 No.5

<P>A simple one-pot approach based on the “benzyl alcohol route” is introduced for the fabrication of highly ordered supercrystals composed of highly uniform 3–4 nm zirconia and rare-earth stabilized zirconia nanoparticles. The as-fabricated supercrystals reach sizes larger than 10 μm and present well-defined 3D morphologies such as flower-like, rhombic dodecahedron, and bipyramids. This system is unique in that the supercrystals are formed in one-step directly in the reaction medium where the nanoparticles are synthesized. The uniformity in nanocrystal shape and size is attributed to the <I>in situ</I> formation of benzoate species that directs the nanoparticle growth and assembly. The low colloidal stabilization of the benzoate-capped nanoparticles in benzyl alcohol promotes the formation of supercrystals in solution by π–π interaction between the <I>in situ</I> formed benzoate ligands attached to neighboring particles. By varying the reaction temperature and the nature of the doping the way the nanobulding blocks assemble in the supercrystals could be controlled. Standard FCC superlattice packings were found together with more unusual ones with <I>P</I>6<I>/mmm</I> and <I>R</I>3̅<I>m</I> symmetries.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-5/nn3010735/production/images/medium/nn-2012-010735_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn3010735'>ACS Electronic Supporting Info</A></P>

Self-Assembly of Dendronized Perylene Bisimides into Complex Helical Columns

Percec, Virgil,Peterca, Mihai,Tadjiev, Timur,Zeng, Xiangbing,Ungar, Goran,Leowanawat, Pawaret,Aqad, Emad,Imam, Mohammad R.,Rosen, Brad M.,Akbey, Umit,Graf, Robert,Sekharan, Sivakumar,Sebastiani, Danie American Chemical Society 2011 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.133 No.31

<P>The synthesis of perylene 3,4:9,10-tetracarboxylic acid bisimides (PBIs) dendronized with first-generation dendrons containing 0 to 4 methylenic units (<I>m</I>) between the imide group and the dendron, (3,4,5)12G1-<I>m</I>-PBI, is reported. Structural analysis of their self-organized arrays by DSC, X-ray diffraction, molecular modeling, and solid-state <SUP>1</SUP>H NMR was carried out on oriented samples with heating and cooling rates of 20 to 0.2 °C/min. At high temperature, (3,4,5)12G1-<I>m</I>-PBI self-assemble into 2D-hexagonal columnar phases with intracolumnar order. At low temperature, they form orthorhombic (<I>m</I> = 0, 2, 3, 4) and monoclinic (<I>m</I> = 1) columnar arrays with 3D periodicity. The orthorhombic phase has symmetry close to hexagonal. For <I>m</I> = 0, 2, 3, 4 ,they consist of tetramers as basic units. The tetramers contain a pair of two molecules arranged side by side and another pair in the next stratum of the column, turned upside-down and rotated around the column axis at different angles for different <I>m</I>. In contrast, for <I>m</I> = 1, there is only one molecule in each stratum, with a four-strata 2<SUB>1</SUB> helical repeat. All molecules face up in one column, and down in the second column, of the monoclinic cell. This allows close and extended π-stacking, unlike in the disruptive up–down alteration from the case of <I>m</I> = 0, 2, 3, 4. Most of the 3D structures were observed only by cooling at rates of 1 °C/min or less. This complex helical self-assembly is representative for other classes of dendronized PBIs investigated for organic electronics and solar cells.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2011/jacsat.2011.133.issue-31/ja204366b/production/images/medium/ja-2011-04366b_0026.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja204366b'>ACS Electronic Supporting Info</A></P>

Self-Organization of Bent Rod Molecules into Hexagonally Ordered Vesicular Columns

Kim, Ho-Joong,Liu, Feng,Ryu, Ja-Hyoung,Kang, Seong-Kyun,Zeng, Xiangbing,Ungar, Goran,Lee, Jeong-Kyu,Zin, Wang-Cheol,Lee, Myongsoo American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.33

<P>Bent-shaped rigid-core molecules with flexible chiral dendrons grafted to the outer side of the bend were synthesized and characterized by circular dichroism, differential scanning calorimetry, X-ray scatterings, and transmission electron microscopy in solution and the solid state. The bent aromatic rods based on hepta- and nonaphenylene with nitrile groups at both ends self-assemble into well-ordered hollow tubular structures in aqueous solution, while the bent rod based on heptaphenylene without nitrile groups showed no apparent aggregations in aqueous solution. In the solid state, the rigid-flexible molecules based on heptaphenylene rod without the nitrile group self-assemble into a 2D oblique columnar structure with the columnar cross-section containing two interlocked molecules. Remarkably, the rigid flexible molecules based on hepta-, nona-, and undecaphenylene with nitrile groups self-assemble into a hexagonal columnar structure with weak 3D order. A model of vesicular channel structure is proposed based on small- and wide-angle X-ray diffraction on oriented fibers, density measurement, reconstruction and simulation of electron density maps, and molecular dynamics simulation. In contrast to the hollow tubular structure found in solution, in the solid both the outside and the interior of the columns are filled by the pendant aliphatic coils. Filling of the interior of these vesicular channels is made possible by some bent rod molecules turning their obtuse apex inward. One in 7, 2 in 8, and 4 in 10 molecules are thus inverted in a column slice in compounds with hepta-, nona-, and undecaphenylene cores, respectively. These are new examples of vesicular double-segregated columnar structures recently discovered in some dendrons.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-33/ja3060904/production/images/medium/ja-2012-060904_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja3060904'>ACS Electronic Supporting Info</A></P>

Self‐Assembly at Different Length Scales: Polyphilic Star‐Branched Liquid Crystals and Miktoarm Star Copolymers

Ungar, Goran,Tschierske, Carsten,Abetz, Volker,Holyst, Robert,Bates, Martin A.,Liu, Feng,Prehm, Marko,Kieffer, Robert,Zeng, Xiangbing,Walker, Martin,Glettner, Benjamin,Zywocinski, Andrzej WILEY‐VCH Verlag 2011 Advanced functional materials Vol.21 No.7

<P><B>Abstract</B></P><P>The diversity of phase morphologies observed recently in star‐branched liquid‐crystalline and polymeric compounds containing at least three immiscible segments is reviewed. Bolaamphiphiles and facial amphiphiles with rodlike aromatic cores, two end‐groups, and one (T‐shape) or two (X‐shape) chains attached laterally to the core, form numerous honeycomblike liquid‐crystal phases, as well as a variety of novel lamellar and 3D‐ordered mesophases. Molecular self‐organization is described in bulk phases and in thin films on solid and liquid surfaces, as well as in Langmuir–Blodgett films. The remarkably reversible formation of mono‐ and trilayer films is highlighted. In the bulk, T‐shaped “rod–coil” molecules without appended end‐groups form predominantly lamellar phases if the core is a straight rod, but the bent‐core variety forms hexagonal honeycombs. Furthermore, self‐assembly of “Janus”‐type molecules, is discussed. Also covered is the diversity of morphologies observed in miktoarm star terpolymers, i.e., polymers with three different and incompatible arms of well defined lengths. Similarities and differences are highlighted between the liquid‐crystal morphologies on the 3–15 nm scale and the polymer morphologies on the scale of 10–100 nm. A separate section is dedicated to computer simulations of such systems, particularly those using dissipative particle and molecular dynamics. Of special interest are the recently synthesised X‐shaped tetraphilic molecules, where two different and incompatible side‐chains are attached at opposite sides of the rodlike core. The tendency for their phase separation produces liquid‐crystal honeycombs with cells of different compositions that can be represented as a plane paved with different colored tiles. The independent variation of chain length and “color” creates the potential for developing a considerable range of complex new 2D and 3D soft nanostructures. Analogous X‐shaped rod–coil compounds with unequal side groups are also of considerable interest, forming tubular lyotropic structures capable of confining strings of guest molecules.</P>

Self-Repairing Complex Helical Columns Generated via Kinetically Controlled Self-Assembly of Dendronized Perylene Bisimides

Percec, Virgil,Hudson, Steven D.,Peterca, Mihai,Leowanawat, Pawaret,Aqad, Emad,Graf, Robert,Spiess, Hans W.,Zeng, Xiangbing,Ungar, Goran,Heiney, Paul A. American Chemical Society 2011 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.133 No.45

<P>The dendronized perylene 3,4:9,10-tetracarboxylic acid bisimide (PBI), (3,4,5)12G1-3-PBI, was recently reported to self-assemble in complex helical columns containing tetramers of PBI as basic repeat unit. These tetramers contain a pair of two molecules arranged side-by-side and another pair in the next stratum of the column turned upside-down and rotated around the column axis. Intra- and intertetramer rotation angles and stacking distances are different. At high temperature, (3,4,5)12G1-3-PBI self-assembles via a thermodynamically controlled process in a 2D hexagonal columnar phase while at low temperature in a 3D orthorhombic columnar array via a kinetically controlled process. Here, we report the synthesis and structural analysis, by a combination of differential scanning calorimetry, X-ray and electron diffraction, and solid-state NMR performed at different temperatures, on the supramolecular structures generated by a library of (3,4,5)<I>n</I>G1-3-PBI with <I>n</I> = 14–4. For <I>n</I> = 11–8, the kinetically controlled self-assembly from low temperature changes in a thermodynamically controlled process, while the orthorhombic columnar array for <I>n</I> = 9 and 8 transforms from the thermodynamic product into the kinetic product. The new thermodynamic product at low temperature for <I>n</I> = 9, 8 is a self-repaired helical column with an intra- and intertetramer distance of 3.5 Å forming a 3D monoclinic periodic array via a kinetically controlled self-assembly process. The complex dynamic process leading to this reorganization was elucidated by solid-state NMR and X-ray diffraction. This discovery is important for the field of self-assembly and for the molecular design of supramolecular electronics and solar cell.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2011/jacsat.2011.133.issue-45/ja208501d/production/images/medium/ja-2011-08501d_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja208501d'>ACS Electronic Supporting Info</A></P>

Planar Alignment of Columnar Discotic Liquid Crystals by Isotropic Phase Dewetting on Chemically Patterned Surfaces

Bramble, Jonathan P.,Tate, Daniel J.,Revill, Derek J.,Sheikh, Khizar H.,Henderson, James R.,Liu, Feng,Zeng, Xiangbing,Ungar, Goran,Bushby, Richard J.,Evans, Stephen D. WILEY‐VCH Verlag 2010 Advanced Functional Materials Vol.20 No.6

<P><B>Abstract</B></P>10.1002/adfm.200902140.abs<P>A novel method of creating planar aligned columnar discotic liquid crystals (cDLCs) on surfaces, which also gives control over the azimuthal angle, is presented. Surfaces are chemically patterned with stripes via microcontact printing of organothiol self‐assembled monolayers (SAMs) on gold, or via deep UV patterning of organosilane SAMs on silicon. These are then used to isolate long droplets of cDLCs by dewetting in the isotropic phase. Upon cooling from the isotropic into the hexagonal columnar phase, polarizing microscopy reveals that the cDLC aligns in a planar orientation. Results for three triphenylene derivatives (HAT‐6, HHTT, H7T) and for a phthalocyanine derivative (8H<SUB>2</SUB>Pc) are presented. H7T and HAT‐6 are found to align with the director perpendicular to the stripe direction, but HHTT and 8H<SUB>2</SUB>Pc align parallel to the stripe direction. This relatively simple new method for creating planar aligned columnar phases of DLCs gives control over the azimuthal angle: a condition required for organic field‐effect transistor applications of cDLCs.</P>