Orientational ordering and dynamics in the columnar phase of a discotic liquid crystal studied by deuteron NMR spectroscopy
摘要:
We report on a deuteron NMR study of quadrupolar splittings and spin-lattice relaxation times T1Q and T1Z as a function of temperature and at two different Larmor frequencies in the columnar phase of hexakis(n-hexyloxy)triphenylene (HAT6). The additive potential method is used to model the quadrupolar splittings, from which the potential of mean torque is parameterized, and the order parameter tensor for an “average” conformer is determined. The small-step rotational diffusion model is used to find the rotational diffusion constants D∥ and D⊥ for the spinning and tumbling motions of the molecular core. It is found that D⊥ is slightly larger than D∥ in contrast with the findings in calamitic liquid crystals. The decoupled model of Dong for correlated internal rotations in the end chains is used for the first time in a discotic liquid crystal. Both jump constants for one- and three-bond motions are nearly independent of temperature, while the jump constant for two-bond motion is thermally activated. The rotational speeds D∥ and D⊥ are some two orders of magnitude slower than a typical charge hopping frequency between the aromatic cores of adjacent molecules in the columns. Thus, to a migrating charge, the “lattice” appears static with disorder being due to the instantaneous displacement of the cores with respect to each other.
Soluble Congeners of Prior Insoluble Shape‐Persistent Imine Cages
作者:Mattes Holsten、Sarah Feierabend、Sven M. Elbert、Frank Rominger、Thomas Oeser、Michael Mastalerz
DOI:10.1002/chem.202100666
日期:2021.6.25
One of the most applied reaction types to synthesize shape-persistent organic cage compounds is the iminecondensationreaction and it is assumed that the formed cages are thermodynamically controlled products due to the reversibility of the iminecondensation. However, most of the synthesized imine cages reported are formed as precipitate from the reaction mixture and therefore rather may be kinetically
Light Responsiveness and Assembly of Arylazopyrazole-Based Surfactants in Neat and Mixed CTAB Micelles
作者:Gunjan Tyagi、Jake L. Greenfield、Beatrice E. Jones、William N. Sharratt、Kasim Khan、Dale Seddon、Lorna A. Malone、Nathan Cowieson、Rachel C. Evans、Matthew J. Fuchter、João T. Cabral
DOI:10.1021/jacsau.2c00453
日期:2022.12.26
photosurfactant (PS), based on cetyltrimethylammoniumbromide (CTAB), and its mixedmicelle formation with CTAB in aqueous solution was investigated by small angle neutron and X-ray scattering (SANS/SAXS) and UV–vis absorption spectroscopy. Upon UV light exposure, PS photoisomerizes from E-PS (trans) to Z-PS (cis), which transforms oblate ellipsoidal micelles into smaller, spherical micelles with larger shell thickness
[EN] SUBSTITUTED XANTHINE DERIVATIVES<br/>[FR] DÉRIVÉS DE XANTHINE SUBSTITUÉE
申请人:CONCERT PHARMACEUTICALS INC
公开号:WO2013155465A8
公开(公告)日:2014-11-13
Neutron Reflection Study of a Double-Chained Sugar Surfactant
作者:D. J. Cooke、J. R. Lu、E. M. Lee、R. K. Thomas、A. R. Pitt、E. A. Simister、J. Penfold
DOI:10.1021/jp960149q
日期:1996.1.1
Neutron reflection and surface tension have been used to investigate the structural features exhibited at the air-liquid interface by an adsorbed layer of the sugar-based nonionic surfactant 7,7-bis[(1,2,3,4,5-pentahydroxyhexanamido)methyl]-n-tridecane. It consists of two glucamide headgroups and two C6H13 alkyl chains, i.e., (C6H13)(2)C(CH2NHCO(CHOH)(4)CH2OH)2, abbreviated to di(C-6-Glu). Isotopic substitution was used to distinguish the chains of the surfactant from the headgroup and solvent distributions. The critical micelle concentration (CMC) was found to be (1.9 +/- 0.1) x 10(-3) M using surface tension measurements, and the latter also indicated that the surface properties were not affected by isotopic substitution. The specular reflection of neutrons has been used to determine the surface concentrations of skeletally deuterated di(C-6-Glu) over the concentration range CMC/400 to 2CMC. The neutron measurements showed the area per molecule A at the CMC to be 66 +/- 3 Angstrom 2, as compared with 60 +/- 10 Angstrom(2) from surface tension measurements. The layer structure has been determined using three different isotopic contrasts at concentrations of CMC and CMC/400. The fit of a two-layer model shows that the total monolayer thickness decreases from 17.5 +/- 1.5 Angstrom at the CMC to 14.5 +/- 1.5 Angstrom at CMC/400, respectively. The kinematic approximation was used to fit the neutron data and an X-ray reflection profile. The most remarkable feature of the structure obtained is the apparent smoothness of the layer. The calculated roughness of the layer at the CMC is 9.7 Angstrom(2) which corresponds exactly to the value expected for capillary waves using the model of a pure liquid. At the CMC the molecule as a whole appears to be tilted about 35-40 degrees away from the surface normal, but at CMC/400 the hydrocarbon chains are approximately normal to the surface while the gluconamide groups are strongly tilted.
Orientational ordering and dynamics in the columnar phase of a discotic liquid crystal studied by deuteron NMR spectroscopy
作者:X. Shen、Ronald Y. Dong、N. Boden、R. J. Bushby、P. S. Martin、A. Wood
DOI:10.1063/1.475833
日期:1998.3.8
We report on a deuteron NMR study of quadrupolar splittings and spin-lattice relaxation times T1Q and T1Z as a function of temperature and at two different Larmor frequencies in the columnar phase of hexakis(n-hexyloxy)triphenylene (HAT6). The additive potential method is used to model the quadrupolar splittings, from which the potential of mean torque is parameterized, and the order parameter tensor for an “average” conformer is determined. The small-step rotational diffusion model is used to find the rotational diffusion constants D∥ and D⊥ for the spinning and tumbling motions of the molecular core. It is found that D⊥ is slightly larger than D∥ in contrast with the findings in calamitic liquid crystals. The decoupled model of Dong for correlated internal rotations in the end chains is used for the first time in a discotic liquid crystal. Both jump constants for one- and three-bond motions are nearly independent of temperature, while the jump constant for two-bond motion is thermally activated. The rotational speeds D∥ and D⊥ are some two orders of magnitude slower than a typical charge hopping frequency between the aromatic cores of adjacent molecules in the columns. Thus, to a migrating charge, the “lattice” appears static with disorder being due to the instantaneous displacement of the cores with respect to each other.