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A Star-shaped Oligo(phenylenevinylene) Liquid Crystal Host with an Anthracene Guest - A Double Nanosegregating Supermesogen
Abstract
Hexasubstituted C3-symmetric benzenes with three elongated shape-persistent oligo(phenylenevinylene) arms and three pyridyl hydrogen bond acceptors have been synthesized. These mesogens assemble in a double helical columnar liquid crystal (LC) structure, owing to the compensation of free spaces between conjugated arms by dimer formation. The void is filled also by up to three anthracene carboxylic acids as guests forming hydrogen bonded supermesogens assembling in columnar LC and soft crystal phases. Thin film fluorescence and solid-state NMR spectroscopy imply a transition from a disordered columnar LC to an unexpected double nanosegregated morphology of a filled soft columnar crystal phase. Here occurs an additional intracolumnar separation of anthracene and oligo(phenylenevinylene) chromophores, besides the general segregation of aliphatic and aromatic building blocks in LC structures. The new type of supermesogens will enable the rational design of host-guest double cables with a wide range of different conjugated building blocks.
... Regarding only the functional building blocks of the liquid crystal, this is called double or triple nanosegregation. Many rather large complex molecular systems further reveal either glassy phases at low temperature or slowly transform to more ordered soft crystals or crystals (Paraschiv et al., 2006;Xiao et al., 2016;Maier et al., 2017). The latter may even improve their performance as quasiparticle transport systems, since in a soft crystal templated by a liquid crystal phase, the overall morphology can be retained but the interaction of functional building blocks are optimized (Ivanov et al., 2006). ...
Liquid crystal design and synthesis are being driven towards always more complexity. The self-assembly of poly- and shape-amphiphiles allow tailoring the soft material structures with double and even triple nanosegregation of functional building blocks. Alignment of the anisotropic liquid crystal is crucial, in order to generate a full control over the material’s function and performance. This procedure often needs an isotropic phase at accessible temperatures without decomposition. The impact of thermodynamic factors, such as cohesive energy density difference and entropy contributions, is discussed in this perspective paper using selected examples. In the process of molecular design such considerations can help to adjust transition temperatures and subsequently, to achieve aligned, complex liquid crystalline matter. This will allow access to new fields of liquid crystal applications.
... Conjugated oligomers and polymers of the arylenevinylene type are in the focus of functional materials for organic electronics [1][2][3][4][5][6]. In addition to the typical units composed of vinylene groups, benzene rings and heterocycles such as thiophene of pyridine, building blocks with heavier atoms [7][8][9] and even transition metals [10] are used to alter the optical and electronic properties. ...
The synthesis and spectroscopic investigation of an acidochromic phenylenevinylene dye with two ferrocene groups is presented.
Sterically crowded, shape-persistent star mesogens with three oligophenylenevinylene arms provide free space in which Blatter radical guests are incorporated by covalent bonds (esters) or supramolecular interactions (hydrogen bonds). The radical...
A chiral urea compound, N,N’-bis(4-(3,4,5-trialkoxyphenylmethyl)phenyl)urea (1a), possessing a long core and six chiral alkyl chains ((S)-citronellyl groups) was designed to construct a double helix supramolecular structure in a liquid crystal phase. As a result, the urea compounds exhibited a hexagonal columnar liquid crystal phase, and the molecules were self-organised into a double helix structure by intermolecular interactions (dipole-dipole interactions, hydrogen bonds, and π-π interactions). Furthermore, the compound’s responsive behaviour to an applied external electric field was investigated, and its phase transition behaviour, column alignment, columnar structures, and electro-responsiveness were compared with those of an achiral urea compound (1b) possessing six n-decyl groups to investigate the effect on introducing the chirality. These results indicated that higher-order structures such as double helices are effective in suppressing thermal motion and delaying polarisation relaxation.
The ability of a star‐shaped tris(triazolyl)triazine derivative to hierarchically build supramolecular chiral columnar organizations through the formation of 1:3 H‐bonded complexes with benzoic acids was studied from a theoretical and experimental point of view. Although the star‐shaped triazine core crystallizes in a non‐ C 3 conformation, the C 3 ‐symmetric conformation is theoretically predicted to be more stable and gives rise to a favourable C 3 supramolecular 1:3 complex upon the interaction with three benzoic acids in their voids. In addition, calculations at different levels (DFT, PM7, and MM3) for the 1:3 host‐guest complex predict the formation of large stable columnar helical aggregates stabilized by the compact packing of the interstitial acids by π‐π and CH···π interactions. The acids restrict the movement of the the star‐shaped triazine cores along the stacking axis causing a template effect in the self‐assembly of the complex. Theoretical predictions correlate with experimental results, since the interaction with achiral or chiral 3,4,5‐(4‐alkoxybenzyloxy)benzoic acids gives rise to supramolecular complexes that organize in bulk in hexagonal columnar mesophases stable at room temperature with intracolumnar order. The existence of supramolecular chirality in the mesophase was determined for complexes formed by acids derived from ( S )‐2‐octanol. Chiral aggregation was also evidenced for complexes formed in dodecane.
Shape‐persistent conjugated mesogens with oligothiophene arms of different lengths have been synthesized. Such mesogens possesses free intrinsic space between their conjugated arms. They form columnar liquid‐crystalline phases, in which the void is filled by dense helical packing in the neat phase similar to an oligo(phenylene vinylene) derivative of equal size. The void can also be compensated by the inclusion of the small acceptor molecule 2,4,7‐trinitrofluorenone. While in solution, the acceptor interacts with the core as the largest π‐surface, it is incorporated between the arms and sandwiched by the star‐shaped neighbours along the columnar assemblies in the solid material. The TNF acceptors are not nanosegregated from the star‐shaped donors, thus the liquid crystal structure converts to a nano‐reservoir for TNF (endo‐receptor). These host‐guest arrangements are confirmed by comprehensive X‐ray scattering experiments and solid‐state NMR spectroscopy. This results in ordered columnar hexagonal phases at high temperatures, which change to helical columnar mesophases or to columnar soft crystals at room temperature.
A new Click procedure have been recently presented, in which a mixture of a female piece (star mesogen with shape-persistent conjugated arms and intrinsic free space) and a male building block (the same star mesogen sterically overcrowded with fullerenes attached via spacers to the arms) self-assemble in highly ordered filled liquid crystal structures. This self-assembly is based on the space-filling of the intrinsic free space and the nanosegregation of the fullerenes in helices. Here we highlight the synthesis of larger phthalocyanine star mesogens and fullerenes attached via long spacers and their mixtures as well as mixtures of the components with the stars of intermediate size and spacer length. While the system with long spacers do not show any alignment and π-stacking, the click procedure reappears successfully for the combination of a large female star and the intermediate male star.
Suzuki cross couplings either between chlorinated N ‐methyliminodiacetic acid (MIDA)‐protected aryl boronates and 1,3,5‐tribromobenzene or between chlorinated aryl bromides and phenyltrisboronic species to star‐shaped 1,3,5‐triphenylbenzenes with different substitution patterns and chloro substituents at the outer phenyl rings were studied. The chlorinated precursors required for the respective reaction were synthesized and characterized. Depending on the used coupling reaction target triphenylbenzenes were isolated in yields between 42% and 88%. Their mesomorphic properties were influenced by the substitution pattern and number of peripheral chlorine atoms. Triphenylbenzene with 3,5‐alkoxy substitution and H in para ‐position self‐assembled into either columnar hexagonal (Col h ) mesophases or a soft crystal. While threefold chloro substitution in meta ‐position of the outer phenyl rings led to stable room temperature Col ho phases, triphenylbenzenes with threefold para ‐chloro or 3,5‐dichloro substitution were non‐mesomorphic. Based on X‐ray diffraction data a helical packing model for the observed phases similar to that of related alkoxy‐substituted triphenylbenzenes was proposed.
A significant impact of resonance-assisted hydrogen-bonding (RAHB) on the liquid crystalline behavior of hydrogen-bonded mesogens is reported and systematically investigated.
In the last 50 years, an important aim of molecular and materials design has been the generation of space for the uptake of guest molecules in macrocycles and cryptands, in dendrimers as monomolecular containers, and recently in porous networks like metal-organic and covalent organic frameworks. Such molecular, oligomeric, and polymeric materials can be applied for sensing, separation, catalysis, drug delivery, and gas storage, among others. The common goal is the recognition of molecules and their uptake into and release from an appropriate space. Typically, completely empty space is unfavorable in crystalline materials. Therefore, the elimination of molecules from the cavities is often accompanied by the collapse of the cavities, that is, by a change in the molecular conformation. In contrast to this solid matter, in which the cavities are rationally designed by covalent or coordinative bonds, liquid crystals (LCs) are fluid materials with high molecular mobility. Thus, the proposal of empty space in LCs is certainly a scientific provocation. However, various recent publications on columnar mesophases claim the existence of pores with low electron density or even completely empty space on the basis of X-ray and solid-state NMR studies. Although the latter may be debated, there are many examples in which LCs take up dopants such as polymerizable monomers in disclination lines, perdeuterated chains in the interstices between columns, or electron acceptors to fill mesogens with incommensurate building blocks, which eventually stabilize the LC phases. It seems that in LC science the generation and usage of free space has been studied only occasionally and were lucky discoveries rather than investigations based on rational design. This Account summarizes the research on the formal generation of void in LCs and highlights that rational design of molecules can lead to unconventional mesophases by efficient filling of the provided space, as was shown with shuttlecock mesogens and discotic mesogens related to the concept of complementary polytopic interactions. The topic was recently further developed by the investigation of shape-persistent star mesogens. Despite the formally empty space between their arms, they all form columnar liquid crystals. Such shape-persistent oligo(phenylenevinylene) molecules fill the void and efficiently nanosegregate by helical packing in columns and deformation of the molecular scaffold at the expense of the torsional energy. This inspired us to fill the intrinsic free space by guest molecules either via supramolecular or covalent bonds or just by physical mixing in order to avoid the increase in torsional energy and to stabilize the structure. This strategy led to complex filled liquid-crystalline matter with high structural control and may in the future be used for the design of organic electronic materials that are easily alignable for device applications.
A series of shape‐persistent star‐shaped oligo(phenylenevinylene) liquid crystals and derivatives with fullerene tethered via spacers of different lengths to one arm have been successfully synthesized. Solution studies by NMR, UV‐Vis and fluorescence spectroscopy reveal the preferential location of the C60 acceptor in the vicinity of the peripheral donor unit, which affects the quenching of the emission of the conjugated stilbenoid scaffold in the donor‐acceptor dyad. The fluorescence is completely absent in the liquid crystal phase owing to the extraordinary hierarchical self‐assembly. The intrinsic free space has to be filled in this family of mesogens either by extremely tight packing of the stars or by the fullerenes as guests. The spacer lengths control the nanosegregation of the C60 units in the cavities of the stars either in independent triple helices or in unprecedented 3D networks, in which fullerenes are positioned at the interface of neighboring columns. Eventually, the clearing temperature of such large complex donor‐acceptor systems can be tuned via an entropy effect defined by the length of the spacer. The accessibility of the isotropic phase without decomposition is an important prerequisite for future alignment studies associated with potential materials application in organic electronics.
We report on our serendipitous finding of the anomalous behavior of a novel liquid crystalline (LC) molecule UH/H, containing a U‐shaped handle. While UH/H itself shows a bicontinuous cubic (Cubbi) phase, UH/H in the presence of pyrene molecules as an external guest forms a hexagonal columnar (Colh) phase without phase separation. Interestingly, even when the pyrene molecules were covalently attached to UH/H (UPy/Py), the molecule exhibited a Colh phase, with a similar columnar geometry to that of UH/H mixed with pyrene molecules (1–4 equiv.). This result means that no matter how the pyrene moieties are incorporated in the LC system, the resultant material exhibited a similar molecular assembly with a columnar geometry. This finding is interesting because UH/H and pyrene molecules do not seem to have specific interactions or shape complementarity to form a columnar assembly, as in the case of UPy/Py. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018. A novel liquid crystalline molecule UH/H, containing a U‐shaped handle, showed a bicontinuous cubic phase by itself; however, in the presence of pyrene molecules as an external guest, it formed a hexagonal columnar phase without phase separation. Interestingly, even when the pyrene molecules were covalently attached to UH/H, the molecule exhibited a hexagonal columnar phase with a similar columnar geometry to that of UH/H mixed with pyrene molecules.
Computational and experimental studies unravel the structural and electronic properties of a novel supramolecular liquid crystal built through a hierarchical assembly process resulting in an H‐bonded melamine rosette decorated with peripheral triphenylenes. The six‐fold symmetry of the mesogen facilitates the formation of a highly organized hexagonal columnar mesophase stable at room temperature. X‐ray diffraction and electron density maps confirm additional intra‐ and intercolumn segregation of functional subunits, and this paves the way for 1D charge transport. Indeed, hole mobilily has been measured and found to be higher than for related mesogens. DFT calculations of HOMO and LUMO levels and parameters such as reorganization energy and transfer integral of the rosette structure have been achieved, and not only validate the columnar organization but also establish the way it translates into a favorable electronic architecture and molecular orbital interactions to promote charge carrier mobility.
Calamitic fluorophores are presented possessing either two phenylethylene or phenylacetylene fragments which are connected via an aromatic entity. The new compounds exhibit smectic C and/or nematic liquid crystalline phases. The chromophores show fluorescence in the blue spectral region. Grafting acrylate functional groups to the termini of naphthalene centred members of the rod-shaped dyes provides new luminescent reactive mesogens. Uniaxial orientation of mixed systems of the acrylate fluorophores with non-emissive reactive benzoate nematogens was achieved by surface-assisted alignment on polyimide orientation layers. The photocrosslinked oriented films display linear polarised photoluminescence upon isotropic excitation.
To probe the influence of electrostatic interactions on the mesomorphic self-assembly and phase behaviour of hybrid liquid crystals a series of crown ether/tyrosine hybrid systems was prepared by Steglich esterification of alkyl N-(tert-butoxycarbonyl)-L-tyrosinates with 4-carboxybenzo-[15]crown-5 and 4-carboxybenzo[18]crown-6. The obtained derivatives allowed further manipulations at the NH functional group and complexation of the crown ether unit with NaI to give neutral or charged hybrid materials. All compounds were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD) measurements. Neither the variation of the N-protecting group, introduction of charge at the N-terminus nor anion exchange (Cl vs. I) resulted in mesomorphism. In contrast, N-Boc-protected and unprotected hybrids formed rectangular columnar (Colr) mesophases with phase widths up to 35 K. NaI complexation switched these neutral thermotropic derivatives into ionic liquid crystals (ILCs) and induced a change of mesophase type from Colr to smectic A (SmA). A comparison of experimentally obtained layer distances and theoretically calculated molecular lengths indicated bilayer SmA formation with interdigitated alkyl chains. Packing models for both mesophase types are proposed and discussed with respect to stabilizing interactions.
The structural impact of hydrogen-donating moieties on the liquid crystalline behavior of hydrogen-bonded assemblies (HBAs) is comprehensively investigated. Therefore, a series of phenol derivatives such as phenol, catechol (CA), resorcinol (RE), hydroquinone (HQ), pyrogallol, hydroxyhydroquinone and phloroglucinol (PHG) was combined with alkoxyazopyridines (Ap-N) yielding 49 new HBAs, which were studied with respect to their mesomorphic properties. The present study revealed significant differences in the liquid crystalline behavior of the structurally diverse assemblies, ranging from the absence of a mesophase to smectic or nematic phases. In contrast to previous studies a compre-hensive crystallographic analysis provides insight into the structure-property relationships of the assemblies and proves a correlation between the supramolecular architecture and the macroscopic properties (= liquid crystallinity). More specifically, comparison of the single crystal data with the 2D X-ray diffraction patterns indicates that linear assemblies tend to form crystalline or smectic phases (for the HQ and RE, respectively), while a bent-shaped assembly yields nematic phases (for CA and PHG). Furthermore, our results suggest that segregation of aliphatic and aromatic segments, as observed in the solid state structures, supports the formation of stable mesophases.
A small series of dendrimers consisting of a star-shaped triphenylbenzene core unit and bulky lateral groups was synthesised and their mesomorphic properties were investigated via differential scanning calorimetry, polarising optical microscopy and small- and wide-angle X-ray scattering (WAXS). The dendrimers showed two enantiotropic hexagonal columnar mesophases. The combination of temperature-dependent and fibre-extruded WAXS revealed a helical arrangement in the low-temperature and a zig-zag orientation in the high-temperature mesophase. Furthermore, at the mesophase-to-mesophase transition, the intracolumnar reorganisation and the intercolumnar lattice extension occurred at different time scales, with the latter process being the slower one.
The synthesis is reported for a main chain polymer in which the repeat units are 2,3,6,7,10,11-hexaphenyltriphenylene moieties linked through flexible dodecyl chains. In compositions with a series of 2,3,6,7,10,11-hexakis(alkoxy)triphenylenes (HATn) this new polymer forms stable hexagonal columnar liquid crystal phases. These are investigated in detail using optical polarised microscopy (OPM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). In these mixtures, suppression of crystallisation and enhancement of the clearing temperatures leads to very wide liquid crystal ranges: much wider than those for the HATn materials on their own. For the longer chain HATn compounds (n = 12-16) a columnar rectangular phase is also observed. The enhancement of the liquid crystal phase range is attributed to stabilising complementary polytopic interactions between the planar aromatic moieties.
Conductivity (dc and ac), ESR-properties and proton relaxation rates of the charge transfer complex Tetrathiafulvalene N,N′-dicyanonaphthoquinonediimine in the temperature range be tween 300 K and 3.8 K are reported. This salt belongs to the unusual group of organic conductors, in which segregated donor and acceptor stacks are associated in a pairwise manner. The physical properties, which are compared with TTF-TCNQ, give evidence of non-stoichiometric charge transfer (ρ ≠ 1). A metal like state can be identified for T> 70 K, as is seen from the weak temper ature dependence of the conductivity (σ
The program HELIX has been devised as a simple aid to understanding the origin and appearance of fibre diffraction patterns from helical structures. Helices are common as preferred conformations in both natural and synthetic macromolecules (e.g. DNA, α-helices, polysaccharides, synthetic polymers), and occur frequently in extended macromolecular aggregates (e.g. actin filaments, myosin filaments, microtubules, amyloid filaments etc.). For this reason, a simple way of visualizing the kinds of diffraction patterns that these structures can give should have educational value and should also be useful as a quick means of testing possible symmetries in structural investigations before embarking on full helical diffraction analysis. Despite its simplicity, there is no other public program that provides these possibilities. The HELIX program, running under Microsoft Windows, is freely available from the CCP13 website (http://www.ccp13.ac.uk).
Stimuli responsive 3D columnar liquid crystals and soft crystals of supramolecular anthracene mesogens were investigated in a study. X-ray scattering, modeling and temperature variable FT-IR studies confirm helical stacked tilted mesogens uncovering unusual lateral hydrogen bonding for the columnar phases transforming by second-order transition from a columnar orthorhombic to a columnar monoclinic phase. The target compounds were synthesized starting from 6-hydroxyanthracene-2-carboxylic acid according to Ihmels and Hibbs.
Hexasubstituierte C3-symmetrische Benzolderivate mit drei Oligophenylenvinylen-Armen und drei Pyridyl- oder Phenyl-Substituenten sind formtreue, im Zentrum sterisch überfrachtete Sternmesogene. Solche Molekülstrukturen weisen große Zwischenräume zwischen ihren Armen auf, die in kondensierten Phasen gefüllt werden müssen. Die reinen Materialien erreichen dies durch ungewöhnliche Dimerbildung und kurzreichweitige helikale Packung in kolumnaren Mesophasen. Für die Pyridylverbindung ist die Mesophase thermodynamisch stabil. Nur dieses Derivat bildet durch Zumischen von unterschiedlichen Carbonsäuren gefüllte, sternförmige Supermesogene. Diese packen nicht mehr als Dimere, sondern als Monomere in kolumnaren Stapeln. Da die Gäste in einer solchen Flüssigkristallphase (LC-Phase) vollständig umschlossen sind, kann man die Wirtmesogene auch als neuartige LC-Endorezeptoren bezeichnen, die zukünftig das Design von kolumnaren funktionalen Strukturen ermöglichen werden.
Hexasubstituted C3 -symmetric benzenes with three oligophenylenevinylene (OPV) arms and three pyridyl or phenyl substituents are shape-persistent star mesogens that are sterically crowded in the center. Such molecular structures possess large void spaces between their arms, which have to be filled in condensed phases. For the neat materials, this is accomplished by an exceptional formation of dimers and short-range helical packing in columnar mesophases. The mesophase is thermodynamically stable for the pyridyl compound. Only this derivative forms filled star-shaped supermesogens in the presence of various carboxylic acids. The latter do not arrange as dimers, but as monomers along the columnar stacks. In this liquid crystal (LC) phase, the guests are completely enclosed by the hosts. Therefore, the host can be regarded as a new LC endoreceptor, which allows the design of columnar functional structures in the future.
© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Sternförmige Oligophenylenvinylen(OPV)-Mesogene sind formtreu und weisen formal zwischen ihren Armen große Freiräume auf. Ein Mesogen mit Armen aus drei Phenylenethenylen-Wiederholungseinheiten packt dicht in einer kolumnar-helikalen Anordnung. Das Anbringen eines Fullerens über einen kurzen Abstandhalter (Spacer) führt zu einer außergewöhnlichen Erhöhung der Mesophasenstabilität. Röntgenstreuung und Modellierung bestätigen die Selbstorganisation zur Tripelhelix, in der Fullerene den Freiraum zwischen den Armen der Sternmesogene perfekt ausfüllen.
Star-shaped oligophenylenevinylene (OPV) mesogens are shape-persistent and possess formally large void space. A mesogen with three styrene repeating units packs densely in a columnar helical arrangement. Attachment of one fullerene through a short spacer results in an exceptional increase of the mesophase stability. X-ray scattering and modeling evidence a triple-helical arrangement in which the fullerene perfectly fills the void space between the arms of the star mesogen.
© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Seit der Entdeckung erster Flüssigkristalle vor 125 Jahren haben sich diese zu einem Wissenschaftsgebiet mit vielseitigen Facetten entwickelt. Dieser Aufsatz beleuchtet aktuelle Entwicklungen auf diesem Gebiet mit dem Schwerpunkt auf dem molekularen Design flüssigkristalliner Materialien und ihrer Selbstorganisation. Im Fokus stehen neue und ungewöhnliche Organisationsformen mit erhöhter Komplexität, wie zelluläre Strukturen, “mehrfarbige” Kompartimentierungen, komplexe periodische und quasiperiodische Anordnungen von sphärischen Aggregaten und Nanopartikeln, sowie resultierende Phänomene wie Ferroelektrizität und Symmetriebruch. Diese werden in Zusammenhang mit anderen geordneten Strukturen in selbstorganisierten Monoschichten, in Multiblock-Copolymeren und periodischen Nanopartikel-Arrays diskutiert. Als Maß der strukturellen Komplexität dienen die Größe der resultierenden periodischen Gitter, der Grad der Kompartimentierung des Raumes und die “logische Tiefe” der Überstrukturen.
Since the discovery of the liquid-crystalline state of matter 125 years ago, this field has developed into a scientific area with many facets. This Review presents recent developments in the molecular design and self-assembly of liquid crystals. The focus is on new exciting soft-matter structures distinct from the usually observed nematic, smectic, and columnar phases. These new structures have enhanced complexity, including multicompartment and cellular structures, periodic and quasiperiodic arrays of spheres, and new emergent properties, such as ferroelctricity and spontaneous achiral symmetry-breaking. Comparisons are made with developments in related fields, such as self-assembled monolayers, multiblock copolymers, and nanoparticle arrays. Measures of structural complexity used herein are the size of the lattice, the number of distinct compartments, the dimensionality, and the logic depth of the resulting supramolecular structures.
Exciplex formation between N,N-dimethylaniline and a series of distyrylbenzene derivatives with varying structures was studied by cyclic voltammetry and fluorescence spectroscopy. The frequency of exciplex emission obeys the Weller equation. Increasing the electron affinity of the acceptor red-shifts emission, with a concomitant decrease in fluorescence efficiency. Increasing the conjugation length of the acceptor decreases its excited state singlet energy more quickly than its electron affinity. As a result, exciplex formation is discouraged with increasing conjugation length.
Part 1 From molecular to supramolecular chemistry: concepts and language of supramolecular chemistry. Part 2 Molecular recognition: recognition, information, complementarity molecular receptors - design principles spherical recognition - cryptates of metal cations tetrahedral recognition by macrotricyclic cryptands recognition of ammonium ions and related substrates binding and recognition of neutral moelcules. Part 3 Anion co-ordination chemistry and the recognition of anionic substrates. Part 4 Coreceptor molecules and multiple recognition: dinuclear and polynuclear metal ion cryptates linear recognition of molecular length by ditopic coreceptors heterotopic coreceptors - cyclophane receptors, amphiphilic receptors, large molecular cage multiple recognition in metalloreceptors supramolecular dynamics. Part 5 Supramolecular reactivity and catalysis: catalysis by reactive macrocyclic cation receptor molecules catalysis by reactive anion receptor molecules catalysis with cyclophane type receptors supramolecular metallo-catalysis cocatalysis - catalysis of synthetic reactions biomolecular and abiotic catalysis. Part 6 Transport processes and carrier design: carrier-mediated transport cation-transport processes - cation carriers anion transport processes - anion carriers coupled transport processes electron-coupled transpoort in a redox gradient proton-coupled transport in a pH gradient light-coupled transport processes transfer via transmembrane channels. Part 7 From supermolecules to polymolecular assemblies: heterogeneous molecular recognition - supramolecular solid materials from endoreceptors to exoreceptors - molecular recognition at surfaces molecular and supramolecular morphogenesis supramolecular heterogeneous catalysis. Part 8 Molecular and supramolecular devices: molecular recognition, information and signals - semiochemistry supramolecular photochemistry - molecular and supramolecular photonic devices light conversion and energy transfer devices photosensitive molecular receptors photoinduced electron transfer in photoactive devices photoinduced reactions in supramolecular species non-linear optical properties of supramolecular species supramolecular effects in photochemical hole burning molecular and supramolecular electronic devices supramolecular electrochemistry electron conducting devices - molecular wires polarized molecular wires - rectifying devices modified and switchable molecular wires molecular magnetic devices molecular and supramolecular ionic devices tubular mesophases. (Part contents).
Two phase diagrams of a six-ring double-swallow-tailed compound are presented where the mixing components involve electron-acceptor compounds. In the mixed phase region, nematic, smectic A and C, cubic and columnar phases are induced. In this way transitions between lamellar, cubic and columnar phases can be realized by variation of the con- centration. The mesophases occurring in these systems have been characterized by X-ray investigations.
The stability of a hydrogen-bonded complex built through inter-molecular hydrogen bonding between carboxylic acid and pyridine fragments has been examined using infrared spectroscopy. Infrared spectra as a function of temperature have been recorded for the 1:1 complex of 4-hexyloxybenzoic acid and trans-4-propoxy-4′-stilbazole from the crystalline state to the isotropic state. A dependence of the stability of the hydrogen bond on molecular orientation is observed clearly in the infrared spectra. The spectra also suggest that the hydrogen bond is an unionized type with a double minimum potential energy.
The use of complementary 2,4,6-triarylamino-1,3,5-triazines and benzoic acids has allowed the preparation of a variety of disklike supramolecules with different substitution patterns around an H-bonded aromatic core. Most of the complexes obtained show columnar mesomorphism promoted by an efficient columnar packing of the aromatic cores surrounded by a minimum of six peripheral tails. The steric requeriments for the appearance of mesomorphic behavior in these supramolecular complexes have been established by X-ray diffraction studies and density calculations based on the parameters of the liquid crystalline organization.
The remarkable phase behavior for binary mixtures of large- core polynuclear aromatic species and small-core discogens cannot be explained simply in terms of net quadrupolar or charge- transfer interactions. The stable π stacking in these mixtures can instead be rationalized by invoking a complimentary polytopic interaction. The picture shows the stacking (in elevation and plan views) between such species.
Several low-aspect-ratio organic molecules [tetrahedral pentaerythritol derivatives, peracylated polyhydroxy compounds and aminoalcohols, a tetraphenylmethane derivative, a tetraphenylstannane, and a tetrahedral zinc bis(1,3-diketonate) all carrying long aliphatic chains] have been synthesized. These compounds were investigated by polarizing optical microscopy and differential scanning calorimetry, and some of them by X-ray diffraction. Most compounds show columnar liquid-crystalline mesophases. Their mesogenic properties are neither caused by a specific anisometric shape of these molecules nor by a strong amphiphilicity as known from conventional liquid crystals. Instead their mesogenity is mainly driven by micro segregation of the incompatible molecular parts (polar central regions and lipophilic alkyl chains) into well-organized different microdomains. It is shown that, in analogy to block copolymers, the mesophase stability rises on enlarging the number of repeat units connected with each other and on increasing the degree of incompatibility between the incompatible segments. During the process of self-organization the average conformation of the molecules is changed in such a way that it allows a most efficient packing of the molecules. Consequently, rigid molecules with a fixed tetrahedral geometry are not mesogenic. The molecules described herein can be regarded as the most simple star-shaped low-aspect-ratio block molecules that form liquid-crystalline phases. They bridge the gap between classical amphiphilic mesogens, several nonconventional dendritic and oligomeric liquid crystals, and mesomorphic block copolymers.
A glowing image: The photoluminescent colors reddish-orange, yellow, and green, are generated from a single liquid-crystalline mixture containing one luminophore (see picture). The colors are easily distinguished by the naked eye and can be reversibly written and erased. Moreover, these luminescent colors can be switched by mechanical and thermal stimuli.
Ring auf Ring: Durch Selbstorganisation formbeständiger Makrocyclen in der flüssigkristallinen Phase unter π-π-Stapelung entstehen leere Nanokanäle mit einem Innendurchmesser von mehr als einem Nanometer und entweder dichten oder durchlässigen Wänden (siehe Bild). Festkörper-NMR-spektroskopischen Studien zufolge befinden sich weder Lösungsmittelmoleküle noch Alkylketten in den Kanälen.
Columnar liquid crystals have recently been developed as dynamically functional anisotropic materials. In this feature article, some recent examples of the materials design and functionalisation of columnar liquid crystals are described. Not only disklike molecules but also molecules with unconventional shapes can form columnar liquid-crystalline assemblies with nanosegregated structures. Moreover use of non-covalent interactions such as hydrogen bonding, ionic and electron donor-acceptor interactions leads to the formation of supramolecular functional columnar materials that are stimuli-responsive. Nanosegregated columnar molecular order can also be used for one-dimensional transportation of electrons, ion and molecules.
This concept article focuses on the simplest branched liquid crystalline (LC) molecules--the three-armed mesogens with arms symmetrically linked to the core. They are basic but fascinating mesogens for the exploration of self-assembling processes into complex, functional, soft materials. Quite a large number of elements of diversity provide the possibility to synthetically program such star-shaped molecules and to control phase formation, if aggregation processes are fully understood. Recently, ABC-cores opened the way to non-symmetric mesogens and, therefore, to the concept of multifunctional materials with defined nanostructures. In the article this outstanding family of mesogens is classified, their peculiar molecular structure and self-assembly are discussed and potential applications are presented, in which this type of mesogen may be beneficial.
The synthesis of dendritic dipeptides (4-3,4-3,5-4)12G2-CH(2)-Boc-L-Tyr-L-Ala-OMe and (4-3, 4-3,5-4)12G2-CH(2)-Boc-D-Tyr-D-Ala-OMe is described. These dendritic dipeptides self-assemble into porous elliptical and circular columns that in turn self-organize into centered rectangular columnar and hexagonal columnar periodic arrays. The transition from porous elliptical to porous circular columns is mediated in a reversible or irreversible way by the thermal history of the sample. A method to determine the dimensions of hollow elliptical and circular columns by the reconstruction of the small-angle powder X-ray diffractograms of the centered rectangular or hexagonal columnar lattices was elaborated. This technique together with wide-angle X-ray experiments performed on aligned fibers provided access to the structural and retrostructural analysis of elliptical supramolecular pores. This procedure is general and can be adapted for the determination of the dimensions of pores of any columnar shape.
In a study of 101 crystal structures of carboxylic acids we have observed a clear trend in the difference between the formally single and formally double C-O bond distances, as observed by X-ray diffraction, with a clear-cut distinction between aromatic acids, where the two distances are similar, and non-aromatic acids, where the two distances distinctly differ by 0.06-0.12 A. A tentative energy classification - within the limits of the many assumptions - and a correlation with the O...O separation over the hydrogen bond indicate that the stability of the carboxylic acid dimer increases as the difference between the two apparent C-O distances becomes smaller, owing to an increasing Coulombic contribution to the dimerization energy. No simple hypothesis is adequate for a complete explanation of the origin, of the details and of the variations of this phenomenon. As often happens in crystal chemistry problems, one is presumably confronted with a balance of several subtle intra- and intermolecular factors.
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