Aggregation behavior of double-chained ammonium amphiphiles containing (cyanobiphenylyl)oxy units

Abstract

A series of amphotropic bis[w-[4(4'-cyanobiphenylyl)oxy] alkyl] dimethylammonium bromides with alkyl spacers of 6-12 methylene units were synthesized. All these new compounds show monotropic liquidcrystalline behavior. UV absorption maxima of vesicles of these compounds are strongly blue shifted relative to the monomer absorption. Upon increasing the temperature the "monomern absorption reappears. Differential scanning calorimetry measurements clearly show a phase transition. This phase behavior is associated with a transition from a "stacked" gel phase to a more mobile liquid-crystalline phase of the vesicle bilayers. Upon spreading these molecules at the water-air interface of a Langmuir-Blodgett trough, an unusually high lift-off area of about 200-250 A2/molecule is observed in the surface pressure-area isotherms. This is associated with a situation in which the molecules are completely stretched on the surface. When the available area is reduced to about 40 AZ/molecule, a situation is obtained in which the tails in a close-packed crystallike arrangement.

Monomer Transfer and Solubilization of Bilayer Vesicles from Double-Chained Ammonium Amphiphiles Carrying Aromatic Units

“…Recently, we have synthesized and investigated ammonium amphiphiles which carry aromatic units. − The aromatic units are all donor-π-acceptor systems and are well-known mesogens. We are especially interested in the aggregation behavior of these compounds in water and at the water−air interface and in their thermotropic liquid crystalline behavior.…”

Electroswitchable red-NIR luminescence of ionic clustomesogen containing nematic liquid crystalline devices

“…Cs 2 Mo 6 Cl 14 , 51 Cs 2 Mo 6 Br 14 , 54 Cs 2 Mo 6 I 14 , 54 bis(w-[4-(4 0 -cyanobiphenylyl)oxy]decyl)dimethylammonium bromide (KATb-Br) 56 and tris(w-[4-(4 0 -cyanobiphenylyl)oxy]decyl)methylammonium bromide (KAT-Br) 55 were obtained by the reported procedure with confirmed analytical data. Starting materials were purchased from Acros, Alfa Aesar and Aldrich, and used without further purification unless otherwise stated.…”

“…Kat + (Scheme 1) was obtained as its bromide salt form according to the reported procedure. 56 In all cases, a stoichiometric amount of Kat-Br was used to exchange the alkali counter cations associated with the cluster unit. Different solvents were used to realize the metathesis reaction with respect to cluster precursor solubility (see the method part for further details).…”

The influence of phenyl and phenoxy modification in the hydrophobic tails of di-n-alkyl phosphate amphiphiles on aggregate morphology

“…The ammonium amphiphiles containing cyanobiphenyl units have a higher main phase transition temperature (T m ) than their aliphatic chain analogue dioctadecylammonium bromide (T m = 45 • C) 13, 14 and UV-VIS spectra of vesicular solutions showed the presence of H-aggregates. 15 Also azobenzene-containing phosphate amphiphiles have been studied. These amphiphiles form bilayer sheets instead of vesicles when dispersed in water and exhibit a blue shift in the UV-VIS spectrum, indicating H-aggregation.…”

“…16 A phosphate amphiphile containing a cyanobiphenyl moiety did not form vesicles. 15 The photophysical behaviour 17 and the phase behaviour 18 of phospholipid derivatives containing aromatic moieties have been studied.…”