Fine tuning of the properties of organically modified heteropolymetalates

Perez, Felix; Bayle, J. P.; Lafontaine, E.; Judeinstein, Patrick

doi:10.1590/s0103-50531997000100015

Cited by 4 publications

(9 citation statements)

References 11 publications

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“…Thus, we have shown The e ect of a lateral substituent in depressing the recently that in a four-ring mesogenic core, it was mesophase stability is larger for more ordered phases like possible to introduce two lateral alkoxy chains on the smectics than for less ordered phases like nematics [ 2]. same side of an inner ring without depleting the liquid For a rigid substituent, the change in the nematic range crystal properties [ 14]. The orientational orderings of is related to its van der Waals radius [3].…”

Section: Introductionmentioning

confidence: 87%

The effect of a lateral aromatic branch on the orientational ordering of laterally alkoxy substituted nematics

Perez¹,

Judeinstein²,

Bayle³

et al. 1997

Liquid Crystals

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Two new mesogenic series have been synthesized. They have the same main core which contains four aromatic rings, with two lateral substituents on the same side of one of the inner rings. One of the substituents is a 4-chlorobenzyloxy group and the second is an alkoxy chain. The positions of the lateral substituents are di erent in the two series. Despite the large aromatic branch, an enantiotropic nematic phase is obtained for most of the compounds. The orientational ordering behaviour of these new compounds has been investigated by C-13 NMR, and two isomeric compounds containing a lateral dodecyloxy chain were chosen for the study. The order parameters of the chain were obtained by a 2D C-13 NMR technique with variable angle spinning. The temperature dependence of the order parameters was determined using the C-13 chemical shifts with slow spinning of the sample parallel to the magnetic ® eld. The ® rst methylene fragment in each lateral substituent of each compound has a positive C± H bond order parameter, implying that this fragment adopts a cisconformation in the nematic phase. The two lateral substituents are folded back along the mesogenic core in opposite directions. The lateral chain is found to be roughly aligned along the molecular long axis imposed by the core, whereas the para-axis of the phenyl ring in the lateral aromatic branch makes a considerable angle with the molecular long axis. It was also found that the di erent patterns of substitution do not a ect the position of the molecular long axis to any large extent.

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Section: Introductionmentioning

confidence: 87%

The effect of a lateral aromatic branch on the orientational ordering of laterally alkoxy substituted nematics

Perez¹,

Judeinstein²,

Bayle³

et al. 1997

Liquid Crystals

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“…These lateral substituents can be Liquid crystals containing the oxyethylene (OE) unit alkoxy chains, substituted benzyloxy fragments or even in polyoxyethylen e (POE) chains or crown ether motifs lateral alkane rings [8][9][10]. The choice of a lateral ring are new materials which possess the unique feature of is of interest as this can increase the thermodynami c dissolving ionic salts and still presenting a mesophase stability of the mesophase.…”

Section: Introductionmentioning

confidence: 99%

“…They combine two interesting properties: the anisoequivalent cores a lateral ring leads to a higher clearing tropy of the liquid crystal phase and also the potential temperature than do two lateral alkoxy chains containing for ionic conductivity as POE chains have [5][6][7][8]. Therethe same number of carbons as the ring [8][9][10]. fore, adding POE chains to a nematogenic structure can…”

Section: Introductionmentioning

confidence: 99%

Ordering of a lateral crown ether and terminal short POE chains in some symmetrical nematogens by 13 C NMR

Sinha¹,

Ramanathan²,

Leblanc³

et al. 2002

Liquid Crystals

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A lateral crown ether fragment can be introduced on symmetrical mesogens containing only three aromatic rings. The replacement of the terminal alkoxy chains by chains containing oxyethylene units decreases the melting and clearing temperatures allowing one to obtain nematic compounds near room temperature. These compounds dissolve LiBF 4 salt only to a small extent, but the nematic arrangement, is thereby destroyed. The carbon chemical shift anisotropy and the local C-H bond order parameters were obtained for the nematic phase for the crown ether fragment and the terminal chains. This study indicates that the crown ether average conformation changes insigni cantly on decreasing the temperature. The lateral crown ether protrudes markedly from the core with the consequence that the molecular shape is far from rod-like in geometry.

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“…As a consequence, in a homologous series, the conventional mesogens, alkyl or alkoxy chains are used melting temperatures can be adjusted by changing the as terminal fragments [1]. The chain conformation in number of carbons within the terminal and/or lateral the solid phase of these compounds is usually trans and chains without aOE ecting too much the nematic range the crystal cohesion which contributes to the value of [5][6][7]. the melting temperature is mainly due to core-core Nematogens containing the oxyethylene unit have two interactions.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, it would be necessary phase. The liquid crystal range presents an odd-even eOE ect as BEN2POE2 possesses a shorter range than the to increase the thermodynami c stability of the mesophase by replacing the two lateral chains by a lateral ring [6], two other compounds within the series. Increasing the chain length does not perturb the relative packing in as we will discuss in the next paragraph, or by increasing the length of the rod [1].…”

Section: Introductionmentioning

confidence: 99%

Nematogens containing oxyethylene units at a lateral or terminal position and their mixtures with salts

et al. 2001

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Short terminal polyoxyethylene chains may be introduced into mesogens containing lateral substituents such as two hexyloxy chains or a crown-ether fragment. These compounds have a large nematic range near room temperature and can dissolve large amounts of the salt LiBF 4 without destroying the nematic arrangment. In the nematic phase, the ions are ordered and the quadrupolar splitting associated with these ions can allow this ordering to be monitored. Increasing the salt concentration does not seem to change the ordering of the individual ions. The 13C thermal evolution of the eld-induced chemical shift in the oxyethylene (OE) units with or without salt does not show any real diOE erence, indicating that the interaction between the ions and the mesogen is small. This means that there is very little change in conformation in the OE unit when adding salt to the mesogen.

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Fine tuning of the properties of organically modified heteropolymetalates

Cited by 4 publications

References 11 publications

The effect of a lateral aromatic branch on the orientational ordering of laterally alkoxy substituted nematics

The effect of a lateral aromatic branch on the orientational ordering of laterally alkoxy substituted nematics

Ordering of a lateral crown ether and terminal short POE chains in some symmetrical nematogens by 13 C NMR

Nematogens containing oxyethylene units at a lateral or terminal position and their mixtures with salts

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