Odd−Even Effects in Azobenzene−Urea Amphiphile Assemblies

Abstract

Azobenzene (Az) derivatives with a urea headgroup, n-{4-[(4-hexylphenyl)azo]phenoxy}alkylurea (6Azn-urea, n = 3, 4, 5, 6, and 7), were synthesized. The characteristics of mono- and multilayers of a series of 6Azn-urea compounds were investigated by means of surface pressure−area isotherm and compressibility measurements, UV−visible and infrared absorption spectroscopy, and X-ray diffraction measurements. Various types of odd−even effects were observed in the spreading behavior and rheological properties in the Langmuir monolayer on the water surface, in the transfer behavior from the water surface to a solid substrate, in the packing state in terms of molecular tilt and Az aggregation in the deposited mono- and multilayers, and in the nature of hydrogen bonding in the multilayers. The carbon parity nature in the 6Azn-urea monolayer should result from the firm fixation at the terminal urea headgroup via intermolecular bifurcated hydrogen bonding, which resembles the situation of self-assembled monolayers attached covalently onto a solid substrate.

Dynamic Photoresponsive Functions in Organized Layer Systems Comprised of Azobenzene-containing Polymers

“…Here, urea-containing Az derivatives are adopted ( Figure 6). [60][61][62][63][64] Urea is chosen as the hydrophilic head because the monolayer of alkylureas shows interesting characteristic properties attributed to the formation of so-called bifurcated (double) hydrogen bond among the urea units on water. [65][66][67][68] When urea is connected with Az unit, further interesting behavior appears as follows.…”

“…3) Obvious and multifarious carbon parity (even-odd) effects are observed with respect to carbon number of the spacer connecting the Az moiety and urea in both monolayers and multilayer systems. 63,64 The crucial role of the bifurcated hydrogen bonding for the appearance of above features is clearly indicated by the chemical modification of urea moiety. 62 Figures 7 displays the area changes of the monolayers of 6Az10-urea, 6Az10-UM, 6Az10-UM2, and 6Az10COOH upon irradiation with UV and visible light at 20 C and 2 mN m À1 .…”

“…63,64 In the -A isotherms of 6Azn-urea (n ¼ 3{7) in the trans form, the limiting area per molecule, which is estimated by extrapolating the steepest slope to zero pressure, indicate systematic alternations with n (figure in the left). For the compounds of odd carbon numbered spacer (n ¼ 3, 5 and 7), the limiting area ranges 0.29-0.30 nm 2 .…”

“…The alternations in the molecular tilt are also consistent with other data of X-Ray analysis and infrared spectroscopy obtained for multilayers. 64 …”

Synthesis and Investigation of Photoisomerization of Some New Azobenzene Carboxylic Acids

“…The reaction mixture was boiled under reflux for 30 min, then 2-tetrahydropyranyl-6-bromohexanate [7] (3-5 mmol) was added and the mixture was boiled for 5-7 h with stirring. The inorganic precipitate was filtered off, washed with acetone and the combined solution was evaporated.…”