Monolayer azobenzene polymers

Monolayers representing two-dimensional arrays of membrane-mimetic assemblies, consisting of azobenzene (poly-L-lysine) with 43 % loading of the photoisomerizable units, were prepared.1441 The compressed trans-azobenzene polymer mono-layer exhibited a surface pressure of 7 mN m 1, whereas photoisomerization of the monolayer to the cis-azobenzene state by UV light decreased the surface pressure to... 

Azobenzene chromophores have been incorporated not only in side chain polymers, but also in other polymer structures. There are several examples of incorporation of azobenzene into the polymer backbone or in the backbone and in the side chain. In these works, the main interest was to realize photoinduced changes of the polymer coil in solution. Some of the main-chain azobenzene polymers were investigated in monolayers at the... 

Liquid crystalline azobenzene polymers can undergo photoisomerization on irradiation at 360 or 450 nm on gold films. This permits changing the refractive index of the film depending upon the wavelength used136. A study has examined the photopolymerization of p-styrene sulphonate counteranions associated with monolayers of disulphide amphiphiles as self-assembled monolayers on gold137. 

Photomechanicd Effects in Azobenzene Polymer Monolayers 15.4.1.1 Macrosize Effect... 

Figure 23. (a) Schematic representation of an anionic surfactant azobenzene derivative monolayer film at the air-water interface. (i>) Schematic representation of the stable monolayer film formed from the polyion complex of anionic surfactant azobenzene derivatives with a cationic polymer. Note the difference in free volume around the reactant chromophores in the two monolayers. 

The peak shift due to aggregation is observed not only in LBK films containing azobenzene chromophores, but also for other chromophores with extended Ji-systems, such as viologen polymers. For monolayers of the poly(p-phenylene sulfonate) 9/ dioctadecyldimethylammonium bromide (DODA) complex, the peak shift due to aggregation results in a piezo-chromic effect—that is, upon compression of the monolayer, a significant shift of the poly(p-phenylene sulfate) A band is observed (see Figure 6.9). This photochromic effect has been shown to be based on the improved 7t-Jt interaction upon compression of the monolayer. ... 

Another class of polymers equipped with azobenzene moieties comprises a-helical polypeptides, in particular pQly(L-glutamate)s and poIy(L-lysine)s. In solution, these azobenzene-modified polypeptides can undergo photoinduced helix-coil transitions. Polypeptides partially (30 to 50%) substituted with azobenzene moieties are surface active and form stable monolayers. Because of the partial substitution, there is sufficient free volume, and the azobenzene moieties can be isomerized in the monolayer. The photoisomerization changes the area per molecule, and the monolayer shows a photomechanical effect. LBK films of a photosensitive poly(L-lysine) with 31 mol... 

Fukuda K., and Nakahara, H. Electronic Sp tra of Oriented Chromophore Sy ems by Incorporation of Azobenzene in the Polymer Main Chain and in Monolayer Forming Amphiphiles. J. Colloid Interface Sci. 98, 555 (1984). 

Seki, T, and Ichimura, K. Formation and Langmuir-Blodgett Deposition of Monolayers of Polyvinylalcohol Having Azobenzene Side Chains. Polym. Commun. 30, 108 (1989). 

Blair, H. S., and McArdle, C. B. Photoresponsive Polymers 2. The Monolayer Behaviour of Photochromic Polymers Containing Aromatic Azobenzene Residues. Polymer 25. 1347 (1984). 

Seki, T., Tanaka, K., and Ichimura, K. Photopolymerization of diacetylene Ijngmuir-Blodgett films on an azobenzene-containing monolayer. Polym. /., 30, 646 (1998). 

Seki, T., and Tamaki, T. Photomechanical effect in monolayers of azobenzene side ch.iin polymers. Chem. Lett., 1739 (1993). 

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