Low Molecular Mass Gelators of Organic Liquids and the Properties of Their Gels

Dendron-mediated self-assembly, disassembly, and self-organization of complex systems have been investigated. The most ideal building blocks would need to display shape persistence in solution and in the solid state, since only this feature provides access to the use of complementary methods of structural analysis. Most supramolecular dendrimers are chiral even when they are constructed from nonchiral building blocks and are equipped with mechanisms that amplify chirality. This poses additional challenges associated with the understanding of the structural origin of chirality in different supramolecular structures through combinations of structural analysis methods. While many supramolecular structures assembled from dendrimers and dendrons resemble some of the related morphologies generated from block-copolymers, they are much more complex and are not determined by the volume ratio between the dissimilar parts of the molecule.

Dendron-Mediated Self-Assembly, Disassembly, and Self-Organization of Complex Systems

Most associate liquid crystals with their everyday use in laptop computers, mobile phones, digital cameras, and other electronic devices. However, in contrast to their rodlike (calamitic) counterparts, first described in 1907 by Vorlander, disklike (discotic, columnar) liquid crystals, which were discovered in 1977 by Chandrasekhar et al., offer further applications as a result of their orientation in the columnar mesophase, making them ideal candidates for molecular wires in various optical and electronic devices such as photocopiers, laser printers, photovoltaic cells, light-emitting diodes, field-effect transistors, and holographic data storage. Beginning with an overview of the various mesophases and characterization methods, this Review will focus on the major classes of columnar mesogens rather than presenting a library of columnar liquid crystals. Emphasis will be given to efficient synthetic procedures, and relevant mesomorphic and physical properties. Finally, some applications and perspectives in materials science and molecular electronics will be discussed.

Discotic Liquid Crystals: From Tailor-Made Synthesis to Plastic Electronics

Supramolecular chemistry, defined as “chemistry outside a molecule”, is at the heart of the development of chemistry of complex systems, molecular devices, ensembles, and nanochemistry.1 This is the chemistry where molecules are able to self-organize, self-assemble, and self-control into systems and the components are often analogues to biological molecules. Metalloporphyrins and metallophthalocyanines are remarkable precursors in supramolecular chemistry, and the rapid development of this chemistry led to assemblies possessing various architectures and properties (photo-, electro-, and catalytic properties and others). Metalloporphyrins are one of the cornerstones on which the existence of life is based, and major biochemical, enzymatic, and photochemical functions depend on the special properties of a tetrapyrrolic macrocycle. However, metalloporphyrins are the only molecules as key elements that require assembly with other elements to form the supramolecular structure, that is, the working device. In natural systems, polypeptides define a given structural organization and hold all the moieties together. Such complex natural devices are not accessible by direct chemical synthesis so far, but their modeling, using simplified designs, has been actively exploited during the last decades. The rapid development of this new area of chemistry has promoted the understanding of the concepts of design and strategies of self-assembly of structures based on intermolecular interactions to result in natural and synthetic supramolecular complexes of metalloporphyrins. Synthetic metalloporphyrin complexes are often used as analogues of natural systems found in photosynthesis, oxygen carriers, and catalysts.2,3 Such research also led to the discovery of new applications of these systems, for example in photodynamic therapy, information storage devices or photoelectrical devices that transform energy in both directions (photocells and lightemitting diodes).4-6 An application of increasing importance is the use of metalloporphyrins as receptors, exploiting their ability to selectively form complexes which can sharply change the spectral properties.7,8 Using molecules that combine different receptor units such as porphyrins and † A.N. Frumkin Institute of Physical Chemistry and Electrochemistry. ‡ Université de Bourgogne. Irina Beletskaya was born in 1933 in Leningrad (USSR). She received her Diploma in 1955, her Ph.D. in 1958, and her Doctor of Chemistry degree in 1963, all at M.V. Lomonosov Moscow State University. The subject for the latter was “Electrophilic Substitution at Saturated Carbon”. She became a Full Professor in 1970. She is currently a head of the Laboratory of Organoelement Compounds at M.V. Lomonosov Moscow State University and a full member (Academician) of Russian Academy of Sciences. She was a recipient of the Lomonosov Prize (1979), the Mendeleev Prize (1982), and the Nesmeyanov Prize (1991). Irina Beletskaya is a chief editor of the Russian Journal of Organic Chemistry. She is the author of more than 1000 articles and a number of monographs. Her current scientific interests are focused on organoelement compounds, transition metal catalysis, and organocatalysis. Chem. Rev. 2009, 109, 1659–1713 1659

Supramolecular chemistry of metalloporphyrins.

Discotic Liquid Crystals.

Novel hybrid triphenylene-carbosiloxane liquid crystalline monomers and star-shaped oligomers have been synthesized and their thermal behavior and liquid-crystalline properties analyzed and characterized. All compounds exhibit a columnar hexagonal phase and show, particularly the oligomers, a small tendency to crystallize. The substitution pattern on the central triphenylene moiety has very different effects on the crystal to columnar phase and columnar to isotropic liquid-phase transitions. A novel sterically induced superlattice has been found, and a model for the microscopic structure is proposed. One compound could be mechanically aligned, leading to well-oriented columnar liquid crystals.

Mesomorphism of Hybrid Siloxane-Triphenylene Star-Shaped Oligomers

New class of bridged diiron(III) complexes with a single hydroxo bridge. The preparation and structure of (.mu.-hydroxo)bis((octaethylporphinato)iron(III)) perchlorate

The magnetic properties of several mixed-valent diruthenium long-chain carboxylates of general formula Ru2(RCO2)4X (X = Cl, DOS, or RCO2, DOS = dodecyl sulfate, and RCO2 = linear aliphatic carboxylate or dialkoxy- or trialkoxybenzoate) were studied in the temperature range 6−400 K. All of the compounds exhibit a strong zero-field splitting (D = ca. 75 cm-1), independent of the nature of the axial anion X or of the equatorial substituent R. In the X = RCO2 series an intermolecular antiferromagnetic (AF) interaction zJ = ca. −2 cm-1 was found, whereas in the case of an X = DOS analogue, this interaction is very weak (−0.2 cm-1). The X = Cl series shows three distinct types of interdimer magnetic exchange:  very weak, moderate (|zJ| ≈ 2 cm-1), or strong (|zJ| > 10 cm-1). One representative complex in this series, Ru2(C4H9CO2)4Cl, has been structurally characterized by X-ray crystallography. Crystal data:  tetragonal system, space group I42d, a = 14.137(3) A, c = 26.246(5) A, and Z = 8. Examination of the st...

Mixed-Valent Diruthenium Long-Chain Carboxylates. 2. Magnetic Properties.

Pyrazine-mediated antiferromagnetic intermolecular exchange in mixed-valent diruthenium tetracarboxylates

A Novel Dimanganese(III) Complex with a Single Hydroxo Bridge. Syntheses, Structures, and Magnetic Susceptibilities of (.mu.-Hydroxo)bis((octaethylporphinato)manganese(III)) Perchlorate and a Monomeric Precursor, Aquo(octaethylporphinato)manganese(III) Perchlorate

Fabio D. Cukiernik

Papers

Mesomorphism of Hybrid Siloxane-Triphenylene Star-Shaped Oligomers

New class of bridged diiron(III) complexes with a single hydroxo bridge. The preparation and structure of (.mu.-hydroxo)bis((octaethylporphinato)iron(III)) perchlorate

Mixed-Valent Diruthenium Long-Chain Carboxylates. 2. Magnetic Properties.

Pyrazine-mediated antiferromagnetic intermolecular exchange in mixed-valent diruthenium tetracarboxylates

A Novel Dimanganese(III) Complex with a Single Hydroxo Bridge. Syntheses, Structures, and Magnetic Susceptibilities of (.mu.-Hydroxo)bis((octaethylporphinato)manganese(III)) Perchlorate and a Monomeric Precursor, Aquo(octaethylporphinato)manganese(III) Perchlorate