13C NMR study of molecular ordering in a discotic columnar mesophase

Rutar, V.; Blinc, R.; Vilfan, M.; Zann, A.; Dubois, Jean

doi:10.1051/jphys:01982004305076100

Cited by 42 publications

(21 citation statements)

References 10 publications

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“…This order parameter is found to be high (= 0.9) and remains almost constant over a wide temperature range [21]. 13C and 1 H NMR studies were also published and lead to similar conclusions [24,25]. Such a dynamic behaviour has not yet been proved in our ionic systems.…”

Section: M2supporting

confidence: 52%

Mesomorphic properties of short chains substituted heteroaromatic salts

et al. 1990

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The synthesis of triaryl-2,4,6 pyrylium tetrafluoroborates substituted by six short (ethyloxy : C2, propyloxy : C3) alcoxy chains has been performed. Classical characterization methods (DSC and optical microscopy) show that these two new compounds present the same columnar phase Dh as that displayed by the other members of the homologous series (C4 to C12). However, these two new compounds are subject to chemical decomposition when heated for a few hours in the mesophase domain of stability but close to Tc. The existence of such a mesophase implies that neighbouring columns be discorrelated. Disordered alcoxy chains are usually assumed to play this role which is however questionable in the case of chains as short as n = 2 or 3. In this case, the BF- 4 anions should play a role in the mesophase formation. In order to obtain information about the behaviour of these anions, we have first performed a comprehensive X ray diffraction study of the whole homologous series. From the intensities of the 2D lattice reflections for all members of the series, we derived a simple model of the molecular organization of this mesophase in which the BF-4 anions are spatially disordered but still located close to the aromatic cores of the cations. We also performed a 19F NMR study of compounds C4, C 5, C8 and C12, which shows that the BF- 4 anions undergo several types of motion in the mesophase. At high temperatures, the spherical reorientation motion of the BF- 4 anions is completed. The onset of this motion may be mainly responsible for discorrelating neighbouring columns and therefore for inducing the Dh phase displayed at high temperatures by compounds C2 and C3

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Section: M2supporting

confidence: 52%

Mesomorphic properties of short chains substituted heteroaromatic salts

et al. 1990

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“…[5][6][7][8][9][10] These discotic molecules tend to form an isotropic liquid phase at high temperature, and stack on top of each other in columns at lower temperatures. The columns also self-assemble into a highly orientationally ordered hexagonal lattice, 11,12 that nevertheless does not exhibit translational order along the column axis because of the liquid-like mobility of the exible branched chains that ll in the intercolumnar space. This liquid crystalline structural stacking is accompanied by a strong overlap of the aromatic p electronic orbitals, that propagates along the columns and gives rise to long-range transport of charge-carriers.…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics of pyrene based discotic liquid crystals confined in nanopores probed by incoherent quasielastic neutron scattering

et al. 2014

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International audienceSemiconducting nanowires made of discotic columnar liquid crystals can be obtained by impregnation into solid nanoporous templates, and provide new opportunities to tailor devices for organic electronics with promising charge carriers transport properties. These properties are tightly related to the self-assembly and molecular dynamics of the discotic columns inside the nanowires. We recently studied and rationalized the formation of different nanostructures in the columnar phase of pyrene derivative discotics nanoconfined in anodic alumina and porous silicon templates ([Cerclier et al., J. Phys. Chem. C, 2012, 116, 18990–18998, Kityk et al., Soft Matter, 2014, 10, 4522–4534]). We now present the molecular dynamics of nano-confined pyrene derivative mesogenic phases as studied by incoherent quasielastic neutron scattering over a broad range of correlation times. The combination of backscattering and time-of-flight techniques has allowed to describe the nature of the molecular motions at play on the pico to nanosecond time scale. The dynamics of the columnar phase is dominated by fluctuations of the lateral chains, while the onset of larger amplitude motions like whole-body reorientations and slow center-of-mass translational diffusion occurs at high temperature in the isotropic phase. Interestingly, nano-confinement does not qualitatively alter the nature of the molecular dynamics, but essentially blocks the long range translational motions and induces broader distributions of correlation times of the fastest local relaxations

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“…That is, the solid polymorphism accompanied by a large amount of transition entropy is important to the appearance of the columnar mesophase. This successive‐conformational‐melting mechanism, derived from the transition entropies, was subsequently confirmed by 2 H and 13 C NMR30–32 and IR spectroscopies33–35 for BH( n ), and also for other discotic mesogens 36–44…”

Section: Successive Conformational Melting In Alkyl Chains: Mechanismmentioning

confidence: 54%

“…This successive-conformational-melting mechanism, derived from the transition entropies, was subsequently confirmed by 2 H and 13 C NMR [30][31][32] and IR spectroscopies [33][34][35] for BH(n), and also for other discotic mesogens. [36][37][38][39][40][41][42][43][44]…”

Section: Successive Conformational Melting In Alkyl Chains: Mechanismmentioning

confidence: 99%

Alkyl chains acting as entropy reservoir in liquid crystalline materials

Sorai

Saito

2003

The Chemical Record

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The roles played by the conformational disordering of alkyl chains in determining the aggregation states of matter are reviewed for liquid crystalline materials from a thermodynamic perspective. Entropy, which is one of the most macroscopic concepts but which has a clear microscopic meaning, provides crucial microscopic information for complex systems for which a microscopic description is hard to establish. Starting from structural implication by absolute (third-law) entropy for crystalline solids, the existence of successive phase transitions caused by the successive conformational melting of alkyl chains in discotic mesogens is explained. An experimental basis is given for the "quasi-binary picture" of thermotropic liquid crystals, i.e., the highly disordered alkyl chains behave like a second component (solvent). A novel entropy transfer between the "components" of a molecule and the resulting "alkyl chains as entropy reservoir" mechanism are explained for cubic mesogens.

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13C NMR study of molecular ordering in a discotic columnar mesophase

Cited by 42 publications

References 10 publications

Mesomorphic properties of short chains substituted heteroaromatic salts

Mesomorphic properties of short chains substituted heteroaromatic salts

Molecular dynamics of pyrene based discotic liquid crystals confined in nanopores probed by incoherent quasielastic neutron scattering

Alkyl chains acting as entropy reservoir in liquid crystalline materials

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