Monolayer azobenzene

Nakahara H and Fukuda K 1983 Orientation of chromophores in monolayers and multilayers of azobenzene derivatives with long alkyl chains J. Colloid Interface Sol. 93 530-9... 

Nakahara H, Fukuda K, Shimomura M and Kunitake T 1988 Moleoular arrangements and photoisomerization of amphiphilio azobenzene derivatives in monolayers and multilayers Mppo/ Kagaku Ka/sh/1001-10... 

Liu Z, Loo B FI, Baba R and Fu]ishima A 1990 Exoellent reversible photoohromio behaviour of 4-ootyl-4 -(5-oarboxyl-pentamethyleneoxy)-azobenzene in organized monolayer assemblies Chem. Lett. 1023-6... 

Zhu T., Yu H.Z., Wang J., Wang Y.Q., Cai S.M., Liu Z.F., Two-dimensional surface enhanced Raman mapping of differently prepared gold substrates with an azobenzene self-assembled monolayer, Chem. Phys. Lett. 1997 265 334-340. 

Pace G, Ferri V, Grave C, Elbing M, Zhamikov M, Major M, Rarnpi MA, Samori P (2007) Cooperative light-induced molecular movements of highly ordered azobenzene self-assembled monolayers. Proc Natl Acad Sci USA 104 9937-9942... 

Organic compounds which show reversible color change by a photochemical reaction are potentially applicable to optical switching and/or memory materials. Azobenzenes and its derivatives are one of the most suitable candidates of photochemical switching molecular devices because of their well characterized photochromic behavior attributed to trans-cis photoisomerization reaction. Many works on photochromism of azobenzenes in monolayers LB films, and bilayer membranes, have been reported. Photochemical isomerization reaction of the azobenzene chromophore is well known to trigger phase transitions of liquid crystals [29-31]. Recently we have found the isothermal phase transition from the state VI to the state I of the cast film of CgAzoCioN+ Br induced by photoirradiation [32]. 

Previously, we recorded UV absorption spectra of the same molecules in spread monolayers on the water surface and in 11-monolayer LB films on solid substrates as shown in Figure 11 [11]. In the case of C8AzoC5, the absorption band due to the it-it transition of the azobenzene moiety in the spread monolayer is largely shifted to... 

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. 

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. 

Weener et al. prepared photo-responsive monolayers from azobenzene modified polypropylene imine) dendrimers which also hold promise in the area of optical data storage [74], A fifth generation polypropylene imine) dendrimer was functionalized with equal amounts of palmitoyl and azobenzene containing alkyl chains, resulting in the formation of an amphiphilic copolymer with a random shell structure (Figure 16.5). 

An interesting example of a system whose components become mechanically bound upon surface immobilization is rotaxane trans-21 (Fig. 13.24), consisting of a ferrocene-functionalized /3-cyclodextrin (fi-CD) macrocycle threaded on a molecule containing a photoisomerizable azobenzene unity and a long alkyl chain.33 A monolayer of trans-21 was self-assembled on a gold electrode. Therefore, the ring... 

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. 

If one makes use of the rather limited information available and given above one may infer that a tilt of between 20° and 30° is normal for straight chain azobenzene derivatives when deposited as LB films, even when a homeotropic phase exists. Such a structure can only be produced in a rather loosely packed film. At the moment it is an open question whether monolayers of these materials exist in the hexatic phase as is the case for fatty acids or whether the structure more nearly corresponds to the smectic-A phase. In the case of the birefringent phase described by Jones et al. [151] it was shown that, once this phase was established, further layers deposited by the LB technique go down in an epitaxial manner. 

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... 

Menzel1811 more recently described the properties and behavior of monolayers prepared from azobenzene-containing poly(L-glutamate)s possessing the structures XIX and XX (n= 2) shown in Scheme 11. These monolayers showed photomechanical effects opposite to those described above for azo-modified poly(L-lysine)s. In fact, they expanded when exposed to UV light (trans—>tis isomerization), and shrank when exposed to visible light (ds— trans isomerization). The expansion was found to be smaller than expected from comparison of the monolayer isotherms obtained from irradiated and nonirradiated solutions. This was attributed to the trans-cis photoconversion of the azo units, which occurs with lower yields in monolayers... 

Higuchi et al.1821 have prepared an interesting photoresponsive polypeptide consisting of two a-helical chains of poly(L-glutamate) of Mw= 11,000, linked by an azobenzene moiety (Scheme 12, XXI). Monolayers of the polypeptide were formed at... 

The investigation was then extended to a monolayer formed from dipalmitoyl phosphatidyl choline and the same amphiphilic photochromic polypeptide XXIII.11211 When the monolayer was kept in the dark, the polypeptide molecules arranged themselves perpendicularly to the membrane (the water/air interface) and formed a bundle of helices which could be observed by atomic force microscopy as a transmembranous particle of about 4 nm in diameter. Irradiation with UV light and the consequent trans—>tis isomerization of the azobenzene moiety caused a bending of the molecular main chain, which in turn produced a destabilization and dena-turation of the bundle of helices in the monolayer. After removal of the light, the polypeptide molecules reverted to their original bundle structure. 1211... 

Figure 5.23 Schematic illustration of the organization of the molecular train monolayer assembly on a gold electrode and its photoinduced translocation. Reprinted from /. Electroanal. Cheat., 497, I. Willner, V. Pardo-Yissar, E. Katz and K. T. Ranjit, A photoactive "molecular train" for optoelectronic applications light-simulated translocation of a /3-cyclodextrin receptor within a stoppered azobenzene-alkyl chain supramolecular monolayer assembly on an Au-electrode, 172-177, Copyright (2001), with permission of Elsevier Science...

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