Photoresponsive assemblies

Organized molecular assemblies containing redox chromophores show specific and useful photoresponses which cannot be achieved in randomly dispersed systems. Ideal examples of such highly functional molecular assemblies can be found in nature as photosynthesis and vision. Recently the very precise and elegant molecular arrangements of the reaction center of photosynthetic bacteria was revealed by the X-ray crystallography [1]. The first step, the photoinduced electron transfer from photoreaction center chlorophyll dimer (a special pair) to pheophytin (a chlorophyll monomer without... 

Kikuchi K, Sumaru K, Edahiro JI et al (2009) Stepwise assembly of micropattemed cocultures using photoresponsive culture surfaces and its application to hepatic tissue arrays. Biotechnol Bioeng 103(3) 552—561... 

Yagai S, Kitamura A (2008) Recent advances in photoresponsive supramolecular self-assemblies. Chem Soc Rev 37 1520-1529... 

Su W, Han K, Luo Y et al. (2007) Pormation and photoresponsive properties of giant microvesicles assembled from azobenzene-containing amphiphilic diblock copolymers. Mac-romol Chem Phys 208 955-963... 

LBK films are highly ordered and densely packed supramolecular assemblies. The packing of the chromophores in LBK films influences their photo-reaction. Therefore, LBK films have to be tailored by the choice of the amphiphilic molecules and the transfer conditions to provide a matrix for the chromophores that has sufficient flexibility and free volume for the photoreaction to occur. On the other hand, the LBK film s structure can be tailored in such a way that the photoreaction of the chromophore enhances the structure or the properties of the entire film. In this way, photoactive films can be designed to show a much more sophisticated photoresponse than that of a chromophore in an inert matrix. 

On the other hand, this procedure for the self-assembled monolayer formation has a drawback. A monolayer adsorbed on a silica plate surface is subjected to the detachment of CRA-CM molecules more or less in polar solvents such as water and alcohols,since the adsorption stems from the hydrogen bond formation. This problem was overcome by the pretreatment of a silica plate surface with an aminoalkylation silylating reagent to introduce amino residues on the surface. A photoresponsive monolayer of... 

This section dealt with the novel functionality of a photoresponsive monolayer to carry out the displacement of liquids simply by photoirradiation as a result of the photocontrol of surface energy. Self-assembled monolayers of CRA-CM are designed and fabricated to ensure sufficient /Z photoisomerizability even in densely packed monomolecular layers, which are quite stable toward solvent treatments. The following critical condition should be met in order to realize the surface-mediated photomanipulation of liquid motion 0 ec < adv In this context, contact-angle hysteresis plays an essential role in this kind of dynamic behavior of liquid displacement. 

The morphological changes discussed in Section 15.4.1.2 were obtained for monolayers at assembled states in 2D. In such an assembled state, secondary effects such as generation of 3D collapse are accompanied on the solid surface. This should be ascribed to the limited allowance of lateral diffusion compared to the rate of the photoisomerization process. For observation of intrinsic photoresponse of the monolayer, separation of the polymer chain is highly desired, ideally on a single-chain level. 

The photoinduced deformation phenomenon of materials is called a photomechanical effect, and it has been so far reported for photoresponsive polymer films and gels [35-43]. When azobenzene is isomerized from the trans form to the cis form, the length of the molecule is shortened from 0.90 to 0.55 nm. The size change of the molecule on photoirradiation is expected to alter the shape of the polymers which contain the azobenzene molecules. However, it is not the case in polymer systems. The transformation in polymer films does not change the polymer shape because of the large free volumes of the polymer bulk. Suitable organization or assembly of the molecules is required for the photoinduced deformation of materials. 

This chapter describes the non-LBL approaches of tandem assembly and interfacial stabilization for the formation of closed shell structures, with an emphasis on ensembles in which NPs constitute the shell. Tandem assembly is a versatile and environmentally friendly route to the formation of useful NP-shelled capsules. In contrast to sacrificial core templating and LBL assembly methods, tandem assembly has the important differentiating feature that it avoids the incineration or solvent dissolution step to generate the hollow interior of the capsule. Enhancements in optical, mechanical, catalytic, and release properties of such materials hold great promise for their application in photoresponsive delivery systems, catalysis, and encapsulation. Interfacial stabilization routes are found to yield NP-shelled structures in the form of emulsions and foams that have enhanced stability over those from conventional, surfactant-based approaches. Unusual interactions of the NP with fluid interfaces have made possible new structures, such as water-in-air foams, colloidosomes, and anisotropic particles. 

Wu L, Tuo X, Cheng H, Chen Z, Wang X. 2001a. Synthesis, photoresponsive behavior, and self assembly of poly(acrylic acid) based azo polyelectrolytes. Macromolecules 34(23) 8005 8013. 

Callari F, Petraia S, Sortino S. 2006. Efighly photoresponsive monolayer protected gold clusters by self assembly of a cyclodextrin azobenzene derived supramolecular complex. Chem Commun 1009 1011. 

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