Azobenzenes photocontrol

We now report the photochromic reaction of an azobenzene in the nanoporous silica film. Since the photochromic behavior is environmentally sensitive, photochromism of organic substances in solid matrices has been investigated to understand as well as to modify the photochromic behavior.[21] Photochromism of azobenzene and its derivatives due to cis-trans isomerization (Scheme I) has widely been investigated. Photocontrol of chemical and physical functions of various supramolecular systems has vigorously been studied by using photochemical configurational change of azobenzene derivatives.[22,23]... 

Fukushima, M., Osa, T., and Ueno, A. (1990) Photocontrol of Molecular Association Attained by Azobenzene-modified Cyclodextrin, Chem. Commun. 15-17. 

It is known from literature that several reversible photochemical reactions, such as geometric isomerism of azobenzene [7], electrocyclic reaction of dihydroindolizines, fulgides and diarylethylenes with heterocyclic groups [8-10], dimerization of anthracene [11], and photochromic reaction of spirocompounds [12] have been also employed to provide photocontrol over metal-ion binding ability of crown ethers. 

The E-Z isomerization of an azobenzene unit was employed in an approach towards photocontrol of the chiral recognition event in a membrane.1581 To this end, (4-(phenyl-azo)phenyl carbamate residues were attached to carbamate-protected glucose units of cellulose and amylose. The photomodulation of the chiral recognition was explained by a change in the ordering of the polymer, leading to a change in solubility. 

As mentioned above, the sol-to-gel phase transitions can be induced reversibly by trans-cis photoisomerization of the azobenzene groups. UV irradiation (330 < X < 380 nm) transforms a part of the trans isomers to the cis. As a consequence of the structural change, the gel state is switched to the sol. Visible irradiation (at X > 460 nm) isomerizes the cis isomers to their trans form and allows the gel to be re-established. The reversible photocontrol of the sol-to-gel phase transition can be monitored by CD spectroscopy. 

Figure 5.28 shows a system used for the photocontrol of electron conductivity within a monolayer. A monolayer of an amphiphile containing azobenzene (the photo controlled part) and tetracyanoquinone (TCNQ, which conducts electrons) was spread on water, resulting in two-dimensional photocontrolled and electrically conductive layers. Isomerizing the azobenzene part between its trans and cis isomer by alternate photoirradiation induced periodic changes in the electrical conductivity of the TCNQ part. The electrical conductivity is limited to a two-dimensional plane here, which embues a different... 

Ueno, A., Takahashi, K., Anzai, J., and Osa, T. Photocontrol of Polypeptide Helix Sense by cis-trans Isomerism of Side Chain Azobenzene Moieties. J. Am. Chem. Soc. 103, 6410 (1981). 

DYNAMIC PHOTOCONTROLS OF MOLECULAR ORGANIZATION AND MOTION OF MATERIALS BY TWO-DIMENSIONALLY ARRANGED AZOBENZENE ASSEMBLIES... 

FIG. 15.1 Photocontrol of various soft materials by azobenzene-containing monolayers. 

Photocontrol of the transport property was also studied for poly(L-glutamic acid) membrane with azobenzene-4-sulfonic acid residues [61]. 

The liquid crystalline characteristics of cinnamate esters have been examined and novel azo bearing systems have been made based on 4-[N-ethyl-N-(2-methacryloyloxyethyl)]amino-4 -(2-cinnamoyloxyethylcarbonyl)-2 -(nitroazoben-zene). Poly[4-(2-methacryloylethoxy)azobenzene] has been found to be valuable for the photocontrol of liquid crystalline alignment as have polymers with benzylidene phthalimidine side chains. Poly(methyl methacrylates) with o-cinnamate side chains undergo polarisation isomerisation resulting in photoalign-... 

The photoinduced flop of the polarization of ferroelectric liquid crystals showing a quick response was achieved by dissolving azobenzene moieties in the liquid crystals.114,11 Photocontrol of the switching behavior of ferroelectric liquid-crystalline polymers (33, Figure 14) was induced by admixing azobenzene derivatives.116... 

K. Ichimura, H. Akiyama, N. Ishizuki, and Y. Kawanishi, Command surfaces. 6. Azimuthal orientation of liquid crystals photocontrolled by an azobenzene pendent polymer, Macromol. Chem., Rapid Commun. 14, 813-917 (1993). 

H. Akiyama, M. Momose, K. Ichimura, and S. Yamamura, Surface-selective modification of poly (vinyl alcohol) films with azobenzenes for in-plane alignment photocontrol of nematic liquid crystals, Macromolecules 28, 288-293 (1995). 

The interesting dual behaviour of porphyrin derivatives is demonstrated by intramolecular electron transfer between an electron-rich tris(4-methylphenyl)porphyrin zinc complex (ZnTPP) and an electron-deficient tris(4-methylphenyl)octafluoroporphyrin (TPOFP) (Teflon porphyrin) free base connected via an azobenzene moiety (438 Scheme 6.209).1250 Upon photolysis at >440 nm, E —> Z photoisomerization (Section 6.4.1) occurs. (Z)-438 can revert to ( )-438 only thermally, because the excited state of the Z-isomer is efficiently quenched by intramolecular electron transfer from ZnTPP to TPOFP, whereas no such interaction is possible in the -isomer because the chromophores are too remote. This approach has been suggested for photocontrolled molecular electronics. 

Asanuma H, Liang X, Yoshida T, Komiyama M. 2001. Photocontrol of DNA duplex formation by using azobenzene bearing oligonucleotides. ChemBioChem 2(1) 39 44. 

Higuchi M, Minoura N, Kinoshita T. 1994. Photocontrol of micellar structure of an azobenzene containing amphiphilic sequential polypeptide. Chem Lett (2) 227 230. 

---