Amphiphile azobenzene linked

For obtaining the information on fabrication of noncentrosymmetric LB films with highly efficient second-order optical nonlinearity, six azobenzene-linked amphiphiles were synthesized as a model compound, and their molecular hyperpolarizabilities (3, monolayer-formation at the air-water interface, and molecular orientation and second-order susceptibilities of the azobenzene-linked amphiphiles LB films were evaluated. The molecular structures of the azobenzene-linked amphiphiles are shown in Fig.2. 

Fig.2. Molecular structures of azobenzene-linked amphiphiles used in this study.

Molecular hyperpolarizabilities p of the azobenzene-linked amphiphiles were estimated using the following equation derived from the two-level model [3] ... 

Fig.3. Surface pressure-area isotherms of azobenzene-linked amphiphiles 1 ...

Table 2 Oder parameter S and effective second-order susceptibilities xS of the alternating LB films of azobenzene-linked amphiphiles and arachidic acid. 

Azobenzene-linked amphiphile C180AZOSN employed for our experiments (Fig.4.) is an intramolecular charge-transfer compound with donor (alkoxy) and... 

Fig.7. Quadratic Stark effect spectrum of a poly(methylmetacrylate) film doped with an azobenzene-linked amphiphile C180AZ0C00H (solid line). Dotted line, broken line, and dash and dotted line show an absorption spectrum of the film, its first derivative, and second derivative, respectively.

Figure 7 shows the quadratic Stark spectrum of a poly(methyl metacrylate) film doped with a azobenzene-linked amphiphile, 4-octadecyloxy-4 -nitroazobenzene. Using eq. (5) and the most characteristic spectral point on the AT/T curves, where dD/dX = 0 and d2D/dXa = 0, the value of Ap was evaluated to be 5.4 debye. Further, the p value of the azobenzene-linked amphiphile was calculated to be 24 x 10 30 esu at a fundamental wavelength of 1064 nm. The p values of azobenzene-linked amphiphiles employed in this study were evaluated by the procedure mentioned here. The values are listed in Table 2 in the section 1.1.1. 

Two azobenzene-linked amphiphiles were dissolved in chloroform and mixture solution with various molar ratio were prepared. The mixed monolayers of C180AZON02 and C180AZOCOOH were spread on a 10 4 M aq. BaCl2 solution... 

In this study, we demonstrated that high orientational order of a polar azobenzene-linked amphiphile was introduced to monolayers by means of the molecular mixing with a homologous amphiphile. Further, enhancement of SHG was observed in the mixed monolayer owing to the improvement of orientation of polar molecules. The mixing technique is expected to develop the construction of noncentrosymmetric LB films with highly efficient optical nonlinearity. 

In nature, polypeptides with amphiphilic structures are known to form transmembrane channels formed by an assembly of several helices, so as to present their polar faces inward and their apolar faces outward. In view of such behavior, the photochromic amphiphilic polypeptide was incorporated into a cationic bilayer membrane composed of dipalmitoyl phosphatidyl choline.11201 Fluorescence and microscopic measurements provided evidence that the polypeptide was able to form bundles of helical molecules analogous to their natural counterparts, which acted as transmembrane channels for K+ ions. Irradiation, and the consequent transacts isomerization of the azobenzene link, caused a bending of the molecular structure and a destabilization of the transmembrane bundles. Therefore, formation of ion permeable channels would be favored or inhibited depending on whether the azo moiety... 

Okuyama, K., Watanabe, H., Shimomura, M., Hirabayashi, K., Kunitake, T., Kajiyama, T., Yasuoka, N. (1986). Molecular and crystal structure of an azobenzene-linked amphiphile, C33H5 N303Br, Bull. Chem. Soc. Jpn., 59 3351. 

Fig. 18 Schematic illustration of the preparation and photoresponsive behavior of the polypeptide XXIII, consisting oftwo amphiphilic helical rods linked by an azobenzene unit, a) Selective saponification of COOCH3 side...

The compound XXIII, consisting of two amphiphilic helical rods linked by an azobenzene moiety, was found to form micelles and ordered aggregates in aqueous solution in the dark, when the azo moiety is in the trans configuration. Photoisomerization of the azo linkage into the cis configuration, and the consequent bending in the structure of the molecules, induced disaggregation and disruption of the micelles.1118,1191... 

With azobenzene-containing amphiphilic BCPs, the photoreaction concerned is the reversible trans-cis photoisomerization of the chromophore upon UV and visible light illumination, respectively. From both the design and synthetic considerations, it is better to link azobenzene moieties onto the hydrophobic polymer. In this case, as schematically illustrated in Fig. 6.1, the hydrophobic block, bearing pendant azobenzene moieties in the more stable trans isomer can form the hydrophobic core of the core-shell micelle or the membrane of the vesicle... 

In another field of current activity, the aggregation behavior of amphiphile molecules is modified and controlled by photoswitching of azobenzenes that are covalently linked as a component of some part or all the amphiphilic molecules. Japanese workers collected a large amount of data on photosensitive artificial membranes based on azobenzene derivatives. ... 

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