Photochemical control

Photoresponsive systems incorporating an azobenzene moiety. The capped crown ether (196), shown as the (E) isomer, was synthesized initially by a high-dilution condensation between diaza-18-crown-6 and 3,3 -bis(chlorocarbonyl)azobenzene (Shinkai et al., 1980). Extraction patterns for the alkali metals differed between the (E) and (Z) isomers giving a clear example of photochemical control of the complexation behaviour. Subsequently, the analogue (197) was synthesized in which 2,2 -azopyridine was used for the cap (Shinkai Manabe, 1984). Photo-... 

Figure 19 Photochemical control of cation transport across membranes...

Monks P.S., Zanis P Schuepbach E., and Penkett S.A. (1999) On photochemical control of ozone at Jungfraujoch (3,580 m asl) in spring based on peroxy radical measurements using FREETEX 96 and model results, Geoph. Res. Abstracts 1(3), 658. 

Thus, the CESD with anionic terminal substituent are able of anionic capping complex formation during the irradiation and thus to achieve photochemical control over binding of metal cations. 

The physical and chemical properties of photoisomerizable molecular films or photoisomerizable polymers are controlled by light. Photochemical control of the formation of liquid crystal phases, or sol-gel transitions,137 381 of polymers containing photoisomerizable components demonstrates signal regulation of the structure and properties of microscopic and macroscopic phases. Physicochemical properties of photoisomerizable membrane-mimetic assemblies such as liposomes,1241 mono-... 

Scheme 11 Photochemical control of electrical contact between a ferrocene-tethered glucose oxidase and the electrode using a thiolated nitrospiropyran as a command interface.

Photochemical Control of LC Alignment by Linearly Polarized Light... 

Fig. 9 Reversible cell adhesion by photochemical control of azobenzene SAMs on gold. Interconversion of Z and E configurations (top). Cell adhesive peptide, RGD, is displayed when SAMs adopt the E configuration at 450-490 nm, and cells adhere and grow (bottom left and right). At 340-380 nm, azobenzene converts to the Z conformation, masking RGD, and cell adhesion is prevented (center bottom). Reproduced from [148] with permission. Copyright Wiley, 2009...

Cooke G, Electrochemical and photochemical control of host-guest complexation at surfaces, Angew. Chem. Int. Ed., 2003, 42, 4860-4870. 

Sauvage has demonstrated both electrochemical and photochemical control over ring motions in a catenate, 18 [57,58]. The observed behavior of the catenate is essentially similar to the analogous rotaxane, the only difference being that the 4-coordinate to 5-coordinate (dpp -> terpy) shuttling process is slower in the catenate and the reverse step is faster. Again, the issue of directionality is not addressed in this system. 

Photochemically Controlled cis-trans Isomerization Molecular Switches... 

We could consider a photochromic organic compound as a reversible dye under photochemical control. Photochromism can be defined as a reversible transformation of chemical species, induced in one or both directions by electromagnetic radiation, between two states having observable light absorptions in different regions. 

Studies on photochromic compounds in connection with chirality have been continuously done from the several viewpoints such as photochemical control of chirality-related liquid crystalline (LC) properties, photochemical control of biological activities by attaching a photochromic compound to biological macromolecules, and use for the optical memory media, as well as the purely scientific interests. 

Photochemical control of properties of SmC LC phase was achieved by doping azobenzene A-4 possessing a chiral carbon atom to a ferroelectric LC A-5 [61]. When the SmC LC is in the surface stabilized state, the bulk dipole moment can be flipped by an external electric field. As the hysteresis curve for the Z form is narrower than that of E form, irradiation of UV light to cause E-... 

The photochemical control of phase change of antiferroelectric LCs wi achieved either by using azobenzenes possessing chiral side chains as d< (A-6) in an antiferroelectric LC or by using azobenzene-containing chiral roelectric LCs (A-7, A-8) [63,64]. 

Case Study II — Photochemical control of ozone in the remote marine boundary layer (MBL) - An elegant piece of experimental evidence for the photochemical destruction of ozone comes from studies in the remote MBL over the southern ocean at Cape Grim, Tasmania (41 In the MBL, the photochemical processes are coupled to physical processes that affect the observed ozone concentrations, namely deposition to the available surfaces and entrainment from the free troposphere. The sum of these processes can be represented in the form of an ozone continuity equation (a simplified version of Equation 2.6), viz... 

Because tropospheric OH is photochemically controlled, a complete understanding of OH requires an understanding of the processes which control the distributions of the species which influence the OH photochemical equilibrium. Of these species the most important are O3, H2O, CH4, CO, and NOx. The levels of atmospheric EhO are largely controlled by the processes of evaporation and condensation and are not discussed here brief discussions of the atmospheric cycles of the other species are presented below. 

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