Effects of Polymerization on Chromophore Stacking in Bilayer Membranes

Abstract

Two novel polymerizable double-chained ammonium amphiphiles carrying mesogenic cyanobiphenylyloxy units have been synthesized containing methacrylate in the headgroup or diacetylene groups in the hydrophobic tails. These compounds form bilayer vesicles upon dispersion in water. Polymerization increases the vesicle stability toward solubilization by a nonionic surfactant. The stacking of the cyanobiphenylyloxy units in the bilayer is directly monitored by the extent of the blue shift of the absorption maximum. Upon polymerization a decrease in blue shift is observed, reflecting a decrease in the ordering of the amphiphile molecules. This effect is stronger when polymerization occurs in the hydrophobic tails than in the headgroup region.

UV/Vis Spectroscopic Monitoring of Polyelectrolyte Adsorption onto Monolayers of Azobenzene Amphiphiles

“…This leads to a change in the excitation energy for the electronic transition and thereby to a band shift in the UV/vis spectra. This phenomenon has been used to investigate the type of organization of azobenzene moieties and other chromophores in self-assembled systems, monolayers, and LB films. ,,− According to the molecular exciton theory, the angle between the transition dipoles and the line connecting them (θ) is one of the parameters defining the direction and size of the band shift (see Figure ). Since the amphiphiles are anchored to the water surface, θ is directly correlated with the tilt of the amphiphiles.…”

Ionic Liquid Crystals: Versatile Materials

“…No nematic phase was observed, despite the fact that precursor [405][Br] shows a monotropic nematic mesophase. 430 A related salt with three cyanobiphenyl groups, [406][Br], was found to form a nematic phase as well. 442 Its cation was successfully combined with molybdenum clusters 391-(397-n) (all [Mo 6 X i 8 X a 6 ] 2− anions; see also the related [C n mim] 2 [Mo 6 Cl 14 ] salts (38-n) that were reported by Mudring and co-workers 622 ) to induce nematic mesomorphism.…”

“…This is not only due to the “straightening” of these chains by metal ion complexation; the stacking into columns also originates from the sequential electrostatic interactions between the ionic moieties in the direction of the columnar axes. Nevertheless, several examples of low molar mass thermotropic ILCs displaying a nematic phase, or a (not commonly observed) columnar nematic phase, can be found in the literature. ,,,,,− [Remark: The quaternary ammonium halide salts based on tris­( n -octadecyl)­amine that were originally claimed to show a nematic phase were later reported to show a SmA phase. , ] Veber and co-workers proposed that the formation of the N C phase by some tricatenar dithiolium salts can be rationalized by the fact that the columns in the lower-temperature Col hex and Col rec phases are stabilized by ionic interactions, so that the 2D hexagonal lattice can “melt” without complete destruction of the columns. , Several neutral nematogenic calamitic LCs with a crown ether moiety and/or short oligo­(ethylene oxide) chains were found to dissolve large amounts of LiBF 4 , NaOTf, or sodium picrate (with complexation of the alkali metal cations by the crown ether moiety if present) and still exhibit a nematic phase. − On the other hand, mesomorphism was lost upon addition of small amounts of LiBF 4 to some derivatives with a lower shape anisotropy . Yoshio et al mentioned a short-range nematic phase for an equimolar mixture of an IL ([C 2 mim]­[BF 4 ]) with a neutral, hydroxyl-terminated LC .…”

“…Apart from lyotropic mesomorphism in chloroform, these compounds show a monotropic thermotropic mesophase, which is very unstable in the case of 390-(405) 4 . No nematic phase was observed, despite the fact that precursor [ 405 ]­[Br] shows a monotropic nematic mesophase . A related salt with three cyanobiphenyl groups, [ 406 ]­[Br], was found to form a nematic phase as well .…”

Adsorption of linear and star-shaped poly(acrylic acid) to model surfaces formed by amphiphiles at the air/water interface

“…This phenomenon has been used to investigate the type of organization of azobenzene moieties and other chromophores in self assembled systems, monolayers and LB films. [13,[37][38][39][40][41][42][43][44] According to the molecular exciton theory [36] the angle between the transition dipoles and the line connecting them (h) is one of the parameters defining the direction and size of the band shift (see Fig. 5).…”