Phasmids and Polycatenar Mesogens

Nguyen, H. T.; Destrade, C.; Malthécte, Jacques

doi:10.1002/adma.19970090503

Cited by 278 publications

(153 citation statements)

References 49 publications

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“…Although the most studied columnar phases are formed by disc-shaped molecules, it is now recognized that such phases can also be formed by dendrimers, [3,4] main-or side-chain polymers with [5,6] or without [7±9] mesogenic moieties, phasmids, [10,11] and board-shaped molecules. [12] For most applications, the organization of the columnar phase at different spatial scales, as well as its temperature and time stabilities are of primary importance.…”

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Templating Crystal Growth at the Nanometer‐Scale with a Monotropic Columnar Mesophase

et al. 2005

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Since their discovery, columnar mesophases have become increasingly important in fundamental research and in practical applications [1,2] due to their peculiar supramolecular architectures that allow one-dimensional charge transport. Although the most studied columnar phases are formed by disc-shaped molecules, it is now recognized that such phases can also be formed by dendrimers, [3,4] main-or side-chain polymers with [5,6] or without [7±9] mesogenic moieties, phasmids, [10,11] and board-shaped molecules. [12] For most applications, the organization of the columnar phase at different spatial scales, as well as its temperature and time stabilities are of primary importance. Indeed, at the local scale the mutual mesogen orientation and intracolumnar ordering directly affects charge migration [13,14] and could possibly be tailored to maximize electron orbital overlap. The electronic and optical properties of the liquid-crystalline (LC) phases also strongly depend on the large-scale structure. In particular, the organization at the mesoscopic scale, ranging from several nanometers to some hundreds of nanometers, must be tailored to control features such as the size and orientation of the LC monodomains. This spatial scale is, however, not easily assessable by conventional techniques [15] as it falls in the gap between the resolution of conventional optical observations and X-ray diffraction. As far as temperature and time stability of the phases are concerned, it is worth noting that the phase diagrams of systems forming LC columnar mesophases are generally complex. This is often not only due to a rich polymorphism of these systems, but also to the heating/cooling irreversibility of phases, i.e., the appearance of monotropic phases. The latter are typically observed on cooling when the phase that is energetically more stable is bypassed because of the slow (re)crystallization kinetics. It is important to note that crystallization of the mesophases was previously studied in some detail for highly ordered smectic phases (G and H) formed by calamitic molecules. [16] Compared to the monotropic nematic and smectic phases formed by polymers, [17,18] the columnar LC monotropic phases have been less extensively studied. [19±22] Two of the first LC molecules displaying monotropic columnar phases were observed by Giroud-Godquin et al. [23] (in metallomesogens) and by Billard et al. [24] (in rufigallol hexa-n-octanoate). In the first case, the room temperature (RT) crystal was formed on cooling via a rectangular columnar phase, which was absent during subsequent heating. [19] In the second case, the columnar monotropic phase was converted into another stable, columnar mesophase before reaching the RT crystalline phase. [20] Another interesting type of monotropic phase formed by HOBT-C8 molecules was studied by Cheng and co-workers, [21,22] who found an intermediate monotropic crystalline phase between a mesophase and a stable crystal. Some other examples of columnar monotropic phases were reported for non-conventional star-...

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Templating Crystal Growth at the Nanometer‐Scale with a Monotropic Columnar Mesophase

et al. 2005

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“…Studies showed that the compounds should have at least three benzene rings to exhibit mesophases. 8 Despite the fact that 1H-imidazole amphiphiles prepared in this work contain only two benzene rings, they form columnar liquid crystals in a concentrated solution and aggregate into bundles at the surface of silicon.…”

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confidence: 85%

Lyotropic columnar liquid crystals based on polycatenar 1H-imidazole amphiphiles and their assembly into bundles at the surface of silicon

2006

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Polycatenar 1H-imidazole amphiphiles, consisting of a 1H-imidazole head connected through a benzene ring to a trialkyloxyphenyl tail, were synthesized and their self-assembling properties investigated. The 1 H NMR and fluorescence spectroscopy studies showed that in nonpolar solvents, the amphiphiles formed reverse micelles in which the hydrophilic imidazole heads aggregated inside the micelles through intermolecular hydrogen bonding and the nonpolar alkyl chains were located at the periphery of the micelles. In concentrated solutions, they formed lyotropic liquid crystals having columnar hexagonal structures. The molecules were arranged in a disk via hydrogen bonding between successive imidazole moieties. When dilute solutions of the amphiphiles in n-hexane (0.1 wt%) were spin-coated on to a plasma-cleaned Si wafer, a band-like structure with a width of 60-100 nm was imaged by AFM. Microscopic fiber bundles with a diameter as large as 13 mm were observed by SEM when the lyotropic liquid crystals in 30 wt% hexane solution were dried on the glass.

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“…A columnar slice contains 14 molecules of 31 and 10 molecules of the larger dendrimers 32 and 33. The postulated model of the molecular organization is derived from that of the lamellar organization, although the increasing ratio value destabilizes the layering by breaking the layers into ribbons as previously observed for lamellar-to-columnar phase transitions exhibited by polycatenar liquid crystals [33], fifth-generation carbosilane dendrimers [34], and statistical liquid-crystalline codendrimers [35]. Each columnar core is made up of mesogenic groups interacting through the cyanobiphenyl groups and is surrounded by the poly(benzyl ether) dendrons including the C 60 units.…”

Section: Codendrimersmentioning

confidence: 99%