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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>
Electro-Functional Octupolar π-Conjugated Columnar Liquid Crystals
Yasuda, Takuma,Shimizu, Tomohiro,Liu, Feng,Ungar, Goran,Kato, Takashi American Chemical Society 2011 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.133 No.34
<P>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.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2011/jacsat.2011.133.issue-34/ja2035255/production/images/medium/ja-2011-035255_0014.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja2035255'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja2035255'>ACS Electronic Supporting Info</A></P>
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>
Body-centered cubic phase in 3-arm star mesogens: a torsional tapping AFM and GISAXS study
Weber, Christa H. M.,Liu, Feng,Zeng, Xiang-bing,Ungar, Goran,Mullin, Nic,Hobbs, Jamie K.,Jahr, Michael,Lehmann, Matthias The Royal Society of Chemistry 2010 SOFT MATTER Vol.6 No.21
<P>The mode of liquid crystal (LC) self-assembly of asymmetric three-arm star oligobenzoate mesogens has been investigated by torsional tapping mode AFM imaging, and by bulk and grazing-incidence X-ray diffraction. It was confirmed that the cubic liquid crystal phase has <I>Im</I>3&cmb.macr;<I>m</I> symmetry and established that it consists of spherical aggregates arranged on a body-centered lattice, rather than having a bicontinuous structure. Molecular simulation suggests that, in spite of their perceived rigidity, the oligobenzoate mesogens are folded, often sharply, within the supramolecular spheres, and that they act effectively as conical objects. The recently introduced torsional tapping AFM technique has allowed high resolution and contrast to be obtained from the soft mobile surface of the samples, showing the (110) plane of highly ordered supramolecular spheres. Notably the fine structure of the observed steps reveals that nearly isolated micelles still preserve their integrity. Finally, the equilibrium habits of the cubic LC droplets were shown by optical microscopy to be polyhedral with crystallographic facets, rather than spherical. This suggests that the air–LC interface is below the roughening transition temperature, which is attributed to the whole micelles rather than the isolated molecules acting as the interacting units.</P> <P>Graphic Abstract</P><P>A combination of torsional tapping atomic force microscopy and X-ray diffraction confirmed a cubic liquid crystal phase in 3-arm star mesogens, displaying faceted gem-like droplets and stable isolated self-assembled micelles at surface steps. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0sm00420k'> </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>