Photoresponsive azobenzenes

Two kinds of photoresponsive azobenzene polyurethane functionalized multiwalled carbon nanotube (AzoPU-MWNT) composites were synthesized by in-situ polycondensation (50). Core-shell structures with MWNTs as hard core and polymer layer as soft shell were formed and the average thickness of the grafted polymers was about 7-10 nm. The AzoPU-MWNT composites showed reversible photoisomerism behavior. 

Photoisomerization of an azobenzene function located in a complex molecule is often accompanied by conformational changes. This approach has again been employed in the construction of photoresponsive crown ethers, a topic which has been the subject of a recent review. Cylindrical ionophores in which two diaza-crown ethers are linked by two photoresponsive azobenzene groups change their ability to bind polymethylene-diammonium salts on irradi-... 

Other modifications include a formamide residue (191), a ring fragmentation product of thymine, which exists as either a cis or a trans conformer. Both isomers are rotated out of the helix, and the bases on either side of (191) occupy the space vacated by it. A pyrene abasic site base pair in DNA duplexes adopts the usual B-form duplex, with the pyrene residue within the duplex stacking on adjacent nucleobases. The abasic site folds back over the opposite strand to shelter the hydrophobic base from exposure to water.The photoresponsive azobenzene analogues (133, R- and 5-forms) have been incorporated into DNA for NMR analysis. Both isomers intercalate between neighbouring base pairs, and the 5-isomer exhibits more disturbance in its duplex structure which is refiected in lower Tms compared to the R-isomer. ... 

Junge, D. M., and McGrath, D. V. (1999). Photoresponsive azobenzene-containing den-drimers with multiple discrete states. /. Am. Chem. Soc. 121,4912 -4913. 

Fig. 9 Synthetic route to the photoresponsive azobenzene containing molecular glasses with two, three, and four azobenzene moieties...

As an example of the first technique, let us consider the case of a polyamide containing photoresponsive azobenzene groups on its main chain (14). The distance between the two para-positions is 9.0 A in trans-azobenzene, and only 5.5 A in the cis-isomer. The cis-trans photoisomerization of these groups is reflected directly by a molecular expansion of the... 

Junge DM, McGrrath DV. 1999. Photoresponsive azobenzene containing dendiimers with multiple discrete states. J Am Chem Soc 121(20) 4912 4913. 

Liu N, et al. 2004. Photoregulation of mass transport through a photoresponsive azobenzene modified nanoporous membrane. Nano Lett 4(4) 551 554. 

Most of the work on photoresponsive azobenzene-containing materials is based on polymer matrices. Numerous chemistries have been utilized to graft azobenzene ligands to various polymer chains. The azobenzene chromophores transfer light energy into conformational changes upon photoirradiation, which can be used to control chemical and physical properties of the materials, such as viscosity, conductivity, pH, solubility, wettability, permeability, transport properties, mechanical properties, and structural properties. 

Liu NG, Dunphy DR, Rodriguez MA, Singer S, Brinker CJ. 2003b. Synthesis and crystallographic structures of a novel photoresponsive azobenzene containing organo silane. Chem Commun 10 1144 1145. 

In a complex based on two a-CDs derivatized at the secondary rim with a molecular chain bearing two recognition sites, a photoresponsive azobenzene unit elose to the rim and a non-photoresponsive hepta-methylene (Cy) moiety connected by an oligoethylene glycol linker, a... 

A photoinert mesogenic group A photoresponsive azobenzene moiety... 

Shinmori et al. have synthesized a diboronic acid saccharide receptor bearing a photoresponsive azobenzene group, 51 that was used as a light-gated saccharide sensor [119]. When the azobenzene unit is switched by photoirradiation, from the more stable trans-conformation to the thermodynamically unfavorable cis-isomer, it shows high D-glucose and D-allose selectivity. The formation of cyclic 1 1 complexes between saccharide and the dye in its cis-geometry explains the selectivity order. 

Abstract Smart polymers based on photoresponsive azobenzene moieties have been extensively explored as potential materials for high capacity optical storage. This chapter reviews different strategies to incorporate azobenzenes into polymeric structures as well as their photoresponse properties. The potential of this type of materials as volume holographic media is summarized with special emphasis on block copolymers and blends. Although side-chain azopolymers has been the most investigated, new macromolecular architectures have been recently proposed and will be briefly presented. 

Shinmori has synthesised a diboronic acid-saccharide receptor bearing a photoresponsive azobenzene group 161, which was used as a light-gated saccharide sensor. When the azobenzene unit is switched by photoirradiation... 

Figure 4.10 Reversible wettability transition of photoresponsive azobenzene monolayer by ultraviolet and visible light irradiation, (a) The shapes of water drops on photoresponsive monolayer with patterned substrate of 40 mm pillar spacing and flat silicon wafer upon UV and Vis irradiation, (b) Reversible wettability transition of photoresponsive monolayer by UV and Vis irradiation.

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