Abstract:Discotic charge transfer twins, a novel class of discotic liquid-crystalline compounds were studied. These compounds consist of triphenylene units (as donors) which are chemically linked via flexible spacers of various lengths to trinitrofluorenone units (acting as acceptor). They display a liquid-crystalline phase over a wide temperature range extending up to 24G26O"C. Based on X-ray analysis a structural model is proposed for the liquid-crystalline phase: the molecules are arranged in columns in such a way t… Show more
“…We note that an increase in r 14 ‘ from 0.55 to 0.60 nm, maintaining all other distances identical, leads to an increase in the estimated interplanar separation from 0.30 to 0.34 nm and a decrease in the interplanar angle from 20° to 10°. Taking account of these reasonable margins of error, the structure obtained here for the intramolecular complex in AN is comparable with the structures of TNF-doped discotic phases, where an average intermolecular distance of 0.34 nm is estimated. 9 Approximate structure of intramolecular complex in AN estimated from interproton distance data derived from the analysis of NOE experiments…”
Section: Resultssupporting
confidence: 78%
“…Evidence for the existence of the complex in this case is provided by the appearance of a well-defined band in the absorption spectra of the benzene/trinitrobenzene mixture, absent in the spectra of the individual components . More recent examples of charge-transfer complexes involving nitro-substituted aromatics are the induced mesophases obtained by doping electron-rich discoid materials with TNF. , The possibility of intramolecular charge-transfer complexes involving TNF-containing flexible molecules has also been demonstrated. ,, All these systems studied comprise strong donor as well as powerful acceptor groups. In the case of AN , the dinitrobenzoyl group is undoubtedly a good electron acceptor.…”
Proton nuclear magnetic resonance spectroscopy has been used to investigate intramolecular interactions between different aromatic groups in a series of diesters. The materials investigated comprise two aromatic groups linked by a 2-methyl-1,3-propanedioxy spacer. This spacer permits U-shaped conformations which place the two terminal aromatic groups close together, parallel in a face-to-face arrangement. For the symmetrical diesters, 1,3-bis(9-anthracenecarbonyloxy)-2-methylpropane (A2) and 1,3-bis[(3,5-dinitrobenzoyl)-oxy]-2-methylpropane (N2), neither the chemical shifts of the aromatic group protons nor the vicinal coupling constants measured in the spacer provide any evidence for a high fraction of U-shaped conformers. In both cases, the conformational distribution of the spacer is similar to that found for 1,3-diacetoxy-2-methylpropane (M2), indicating that the planar aromatic groups in A2 and N2 experience no significant mutual attractive interactions. In contrast, substantial upfield shifts are observed in the resonance frequencies of all aromatic protons in the anthacenyl and 3,5-dinitrophenyl groups of the unsymmetrical diester, 1-(9-anthracenecarbonyloxy)-3-[(3,5-dinitrobenzoyl)oxy]-2-methylpropane (AN), relative to those for the aromatic protons of the respective monoesters and symmetrical diesters. Analysis of the temperature dependence of the vicinal coupling constants indicates highly populated gauche states of the two central C-C bonds of the spacer chain, consistent with a total fraction of U-shaped conformers of about 80% at ambient temperature. Transient nuclear Overhauser effect experiments yield values of between 0.4 and 0.6 nm for average distances between protons on the dinitrophenyl ring and those on the anthracenyl ring, implying a distance of approximately 0.3 nm between the planes of the two aromatic groups. The stabilization of the U-shaped conformers in AN is rationalized in terms of quadrupole interactions between the two aromatic groups. The quadrupole moments associated with the two aromatic groups in AN have opposite sign, resulting in a significant attractive interaction when the groups are oriented face-to-face. For the symmetrical diesters, A2 and N2, the interacting aromatic groups have identical quadrupole moments and the interaction is repulsive in the face-to-face arrangement.
“…We note that an increase in r 14 ‘ from 0.55 to 0.60 nm, maintaining all other distances identical, leads to an increase in the estimated interplanar separation from 0.30 to 0.34 nm and a decrease in the interplanar angle from 20° to 10°. Taking account of these reasonable margins of error, the structure obtained here for the intramolecular complex in AN is comparable with the structures of TNF-doped discotic phases, where an average intermolecular distance of 0.34 nm is estimated. 9 Approximate structure of intramolecular complex in AN estimated from interproton distance data derived from the analysis of NOE experiments…”
Section: Resultssupporting
confidence: 78%
“…Evidence for the existence of the complex in this case is provided by the appearance of a well-defined band in the absorption spectra of the benzene/trinitrobenzene mixture, absent in the spectra of the individual components . More recent examples of charge-transfer complexes involving nitro-substituted aromatics are the induced mesophases obtained by doping electron-rich discoid materials with TNF. , The possibility of intramolecular charge-transfer complexes involving TNF-containing flexible molecules has also been demonstrated. ,, All these systems studied comprise strong donor as well as powerful acceptor groups. In the case of AN , the dinitrobenzoyl group is undoubtedly a good electron acceptor.…”
Proton nuclear magnetic resonance spectroscopy has been used to investigate intramolecular interactions between different aromatic groups in a series of diesters. The materials investigated comprise two aromatic groups linked by a 2-methyl-1,3-propanedioxy spacer. This spacer permits U-shaped conformations which place the two terminal aromatic groups close together, parallel in a face-to-face arrangement. For the symmetrical diesters, 1,3-bis(9-anthracenecarbonyloxy)-2-methylpropane (A2) and 1,3-bis[(3,5-dinitrobenzoyl)-oxy]-2-methylpropane (N2), neither the chemical shifts of the aromatic group protons nor the vicinal coupling constants measured in the spacer provide any evidence for a high fraction of U-shaped conformers. In both cases, the conformational distribution of the spacer is similar to that found for 1,3-diacetoxy-2-methylpropane (M2), indicating that the planar aromatic groups in A2 and N2 experience no significant mutual attractive interactions. In contrast, substantial upfield shifts are observed in the resonance frequencies of all aromatic protons in the anthacenyl and 3,5-dinitrophenyl groups of the unsymmetrical diester, 1-(9-anthracenecarbonyloxy)-3-[(3,5-dinitrobenzoyl)oxy]-2-methylpropane (AN), relative to those for the aromatic protons of the respective monoesters and symmetrical diesters. Analysis of the temperature dependence of the vicinal coupling constants indicates highly populated gauche states of the two central C-C bonds of the spacer chain, consistent with a total fraction of U-shaped conformers of about 80% at ambient temperature. Transient nuclear Overhauser effect experiments yield values of between 0.4 and 0.6 nm for average distances between protons on the dinitrophenyl ring and those on the anthracenyl ring, implying a distance of approximately 0.3 nm between the planes of the two aromatic groups. The stabilization of the U-shaped conformers in AN is rationalized in terms of quadrupole interactions between the two aromatic groups. The quadrupole moments associated with the two aromatic groups in AN have opposite sign, resulting in a significant attractive interaction when the groups are oriented face-to-face. For the symmetrical diesters, A2 and N2, the interacting aromatic groups have identical quadrupole moments and the interaction is repulsive in the face-to-face arrangement.
“…The compounds studied here are composed of chemically connected donor (triphenylene) and acceptor (trinitrofluorenone (TNF)) fragments. These twin and triple discotic molecules form homogeneous columnar mesophases in the bulk state as have been demonstrated earlier . For these compounds, the pressure−area behavior of the monolayers at the air−water interface is studied and LB films with a limited number of the molecular layers are fabricated.…”
Section: Introductionmentioning
confidence: 71%
“…The synthesis, thermal behavior, and structure in the bulk mesophase of the donor−acceptor twin molecules 1 and 2 are described elsewhere …”
X-ray and atomic force microscopy observations reveal features of
the surface morphology of Langmuir−Blodgett (LB) films from discotic donor−acceptor molecules with strong
core-to-core interactions caused
by a charge-transfer (CT) complexation. The compounds are designed
to be twin and triple molecules
composed of chemically connected donor (triphenylene) and
acceptor (trinitrofluorenone) fragments which
display liquid crystalline structure in the bulk state. The LB
films from these compounds possess edge-on
orientation of molecules within monolayers with a smooth surface on a
submicron scale but with substantial
macroscopic imperfections. These imperfections are represented by
the micron size fractures and ruptures
apparently caused by local deformations and tensions during transfer of
the discotic monolayers from the
air−water interface to a solid substrate. It is suggested that
this is due to the excessive rigidity of the
monolayers caused by the stiffness of the columns with positional
intracolumnar ordering enhanced by
the strong intracolumnar CT interactions.
“…triphenylene is an electron-rich molecule and it can form charge-transfer (C-T) complex with electron acceptor, such as trinitrofluorenone (TNF), and stabilize the columnar assembly. Although nitrogen-containing heteroaromatic rings such as pyridine [26][27][28], pyrazine [29,30], pyrimidine [31] and pyridazine [11] and others such as 2,4,7-trinitrofluorenone (TNF) [32][33][34][35] and so on [12,36] have been employed as electron acceptors, the heterocycle 1,2,3-triazole as an electron acceptor in the discotic dimer system has not been reported. As the triphenylene moiety is electron-rich and triazole moiety electron-poor, the C-T complex formed or not in the columnar assembly should be further verified.…”
Click chemistry between alkynes and azides high efficiently produces triazoles and would be a convenient tool for synthesis of discotic liquid crystal dimers, oligomers and polymers. In this report, triphenylenes containing terminal alkynes and azides were prepared, and the cycloaddition reaction (click chemistry) between them catalyzed by CuI-Et 3 N in toluene produced discotic liquid crystal dimers in high yield and good selectivity. The dimers and intermediates have been fully characterized by 1 H NMR and high resolution MS. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) results show the dimers possess columnar mesophase in wide temperature range from very low temperature. The triazole moiety in the dimer can act as electron and hydrogen bond acceptor, and ionic forming part, rich chemical and physical properties can be expected from these new structure discotic dimers.
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