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

Artificial Molecular Rotors

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Chiroptical Molecular Switches

Stereoselective Addition to N-Activated Pyridines James A. Bull,‡ James J. Mousseau, Guillaume Pelletier,† and Andre ́ B. Charette*,† †Department of Chemistry, Universite ́ de Montreál, P.O. Box 6128, Station Downtown, Montreál, Queb́ec, Canada H3C 3J7 ‡Department of Chemistry, Imperial College London, South Kensington, London SW7 2AZ, U.K. Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA

Synthesis of Pyridine and Dihydropyridine Derivatives by Regio- and Stereoselective Addition to N-Activated Pyridines

The hierarchical self-assembly of disc-shaped molecules leads to the formation of discotic liquid crystals. These materials are of fundamental importance not only as models for the study of energy and charge migration in self-organized systems but also as functional materials for device applications such as, one-dimensional conductors, photoconductors, light emitting diodes, photovoltaic solar cells, field-effect transistors and gas sensors. The negative birefringence films formed by polymerized nematic discotic liquid crystals have been commercialized as compensation foils to enlarge the viewing angle of commonly used twisted nematic liquid crystal displays. To date the number of discotic liquid crystals derived from more than 50 different cores comes to about 3000. This critical review describes, after an in-depth introduction, recent advances in basic design principles and synthetic approaches towards the preparation of most frequently encountered discotic liquid crystals.

Self-organization of disc-like molecules: chemical aspects

Mono-, bis-, tris-, and tetra-kis(1-azulenylethynyl)benzene and mono- and bis(1-azulenylethynyl)thiophene derivatives 5-10 have been prepared by Pd-catalyzed alkynylation of ethynyl arenes with 1-iodoazulene derivative or the 1-ethynylazulene derivative with tetraiodobenzene and iodothiophenes under Sonogashira-Hagihara conditions Compounds 5-10 reacted with tetracyanoethylene in a [2+2] cycloaddition reaction to afford the corresponding 1,1,4,4,-tetracyano-2-(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-3-butadienyl chromophores 12-16 in excellent yields, except for the reaction of the tetrakis(1-azulenylethynyl)benzene derivative 1,1,4,4,-Tetracyano-2,3-bis(1-azulenyl)butadiene (17) was also prepared by the similar reaction of bis(1-azulenyl)acetylene (11) with tetracyanoethylene (TCNE) The redox behavior of novel azulene derivatives 12-17 was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed multistep electrochemical reduction properties Moreover, a significant color change was observed by visible spectroscopy under electrochemical reduction conditions

Synthesis, properties, and redox behavior of mono-, bis-, and tris[1,1,4,4,-tetracyano-2-(1-azulenyl)-3-butadienyl] chromophores binding with benzene and thiophene cores.

Creation of Stabilized Electrochromic Materials by Taking Advantage of Azulene Skeletons

The Diels-Alder reaction of di-2-azulenylacetylene with tetraphenylcyclopentadienone afforded 7,8,9,10-tetraphenyldiazuleno[2,1-a:1,2-c]naphthalene in one pot via autoxidation of the presumed 1,2-di-2-azulenylbenzene derivative. In contrast, a similar reaction of bis(1-methoxycarbonyl-2-azulenyl)acetylene with tetraphenylcyclopentadienone gave the 1,2-di-2-azulenylbenzene derivative. The following cyclodehydrogenation reaction of the benzene derivative with iron(III) chloride afforded diazuleno[2,1-a:1,2-c]naphthalene 6,11-bismethoxycarbonyl derivative. The redox behavior of these novel diazuleno[2,1-a:1,2-c]naphthalenes was examined by cyclic voltammetry (CV). These compounds exhibited two-step oxidation waves at +0.22 to +0.71 V upon CV, which revealed the formation of a radical cation and dication stabilized by the fused two azulene rings under the electrochemical oxidation conditions. Since the 1,2-di-2-azulenylbenzene derivative was oxidized at higher oxidation potentials (+0.83 and +1.86 V), the fusion of the two azulene rings to naphthalene increased electron-donating properties because of the formation of a closed-shell dicationic structure. Formation of the radical cation was characterized by UV-vis spectroscopy under the electrochemical oxidation conditions, although no evidence was obtained for the presumed dication under the conditions of the UV-vis spectroscopy measurement.

Synthesis and two-electron redox behavior of diazuleno[2,1-a:1,2-c]naphthalenes.

This paper describes the cyclotrimerization reaction of di(2-azulenyl)acetylenes (2a,b) catalyzed by Co2(CO)8 to produce hexa(2-azulenyl)benzene derivatives (1a,b). The cyclooligomerization of 2a and 2b utilizing CpCo(CO)2 as a catalyst produced (η5-cyclopentadienyl)[tetra(2-azulenyl)cyclobutadiene]cobalt complexes (3a,b). The redox behavior of hexakis(6-octyl-2-azulenyl)benzene (1b), bis(6-octyl-2-azulenyl)acetylene (2b), and the cobalt complexes 3a and 3b along with 6-octyl-2-phenylazulene (19) was examined by cyclic voltammetry (CV). The reduction of compound 1b exhibited multiple-electron transfers in one step upon CV with a reduction potential similar to that of compound 19. However, the CVs of compounds 2b, 3a, and 3b were characterized by stepwise waves because of the reduction of each azulene ring. The mesomorphic behaviors of 1b, 2b, and 19 were also studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD) techniques. A new series of azu...

Noboru Morita

Papers

Synthesis, properties, and redox behavior of mono-, bis-, and tris[1,1,4,4,-tetracyano-2-(1-azulenyl)-3-butadienyl] chromophores binding with benzene and thiophene cores.

Creation of Stabilized Electrochromic Materials by Taking Advantage of Azulene Skeletons

Synthesis and two-electron redox behavior of diazuleno[2,1-a:1,2-c]naphthalenes.

Synthesis and properties of hexakis(6-octyl-2-azulenyl)benzene as a multielectron redox system with liquid crystalline behavior.

Recent Advances in the Developmentof Methods for the Preparation of Functionalized Azulenes for ElectrochromicApplications