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Azobenzenes Subject

The second subject is concerned with cis and (runs isomers. The tratu isomer has the higher Xma. value (except for azobenzene) and the larger mai. This will be apparent from the data in Table XIII. [Pg.1148]

Mechanistically these isomerizations have been investigated very little, in contrast to those of azo compounds such as azobenzene and its derivatives. This subject is not... [Pg.147]

We have demonstrated that a chiral vesicle composed of di-palmitoyl-L- a-phosphatidylcholine(l-DPPC) doped with the azobenzene containing amphiphiles shown in Scheme 2 is a subject to photochemically triggered phase transition and exhibits a non-linear photoresponse in terms of ICD appearing at the absorption band of azobenzene. [Pg.216]

Larson et al. (1992) studied the photosensitizing ability of 2, 3, 4, 5 -tetraacetylriboflavin to various organic compounds. An aqueous solution containing aniline was subjected to a medium-pressure mercury arc lamp (X >290 nm). The investigators reported that 2, 3, 4, 5 -tetraacetylribofiavin was superior to another photosensitizer, namely riboflavin, in degrading aniline. Direct photolysis of aniline without any photosensitizer present resulted in a half-life of 23 h. In the presence of riboflavin and 2, 3, 4, 5 -tetraacetylribofiavin, the half-lives were 1 min and 45 sec, respectively. Photoproducts identified in both reactions were azobenzene, phenazine, and azoxybenzene. [Pg.106]

Since it was observed that absorption ceased after 3.3 atoms of hydrogen were taken up per mole of nitrobenzene, Equation 14 is shown as producing 4 moles of cyanocobaltate(II) per mole of substrate via reaction of the latter with CoH. Since further absorption of hydrogen occurred only upon introduction of alkali, it is implied that an intermediate complex, X, is formed which is not subject to further reaction with CoH but may be decomposed by alkali. The stoichiometry of this equation requires formulation of complex X as [Co(CN)5(C6H5NH)]—3. However, since absorption ceased after two atoms of hydrogen had been absorbed per atom of cobalt present, it is implied that a binuclear complex is formed, perhaps involving phenylhydroxylamine, azobenzene, or some other reduction intermediate. [Pg.217]

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-... [Pg.390]

The photoisomerization mechanism in aminoazobenzene- and pseudo-stilbene-type compounds has attracted far less attention than the mechanism for azobenzenes. In pseudo-stilbenes, the (n,7t ) state is buried under the intense it —> Jt band and cannot be populated selectively. No state-specific quantum yields are available because the yields are independent of the exciting wavelength.There is only a very narrow experimental basis for a discussion of these two mechanisms. However, this may change when pseudo-stilbenes are subjected to ultrashort-time experiments. [Pg.37]

The first pair of polymers (Figure 13.1) studied in our laboratory were the polyacrylate (pDRlA) and the polymethacrylate (pDRlM) derived from Disperse Red 1. Their glass transition temperatures were 91° and 129°C, respectively. Disperse Red 1 and the polymers derived from it have a maximum absorbance at about 480 nm. The actual maximum wavelength depends on the conditions, such as in film or in solution, and on the possibility of association of the chromophores. This absorbance is associated with the 7t - 7t transition of the trans azobenzene isomer. A thin film of one of the polymers can be subjected to laser irradiation (either 488 or 514 nm are close enough to the... [Pg.402]

It has been Icnown for years that a decrease in the phase transition temperature of azobenzene containing LC is induced by trans -cis photoisomerization (23). Smectic LC of 4-alkyl-4 -cyano-biphenyl is subjected to phase transition by photoisomerization of azobenzene leading to a reversible change in the threshold voltage for electrohydrodynamic instability (24). None of them described the concept of image amplification. [Pg.439]

Figure 11.5. Changes in orientation of azobenzene mesogens for two films of azo-SCLCP-grafted SBS, under 500% strain, subjected to repeated cycles of unpolarized UV irradiation for orientation loss and unpolarized visible irradiation for orientation recovery. Source Bai and Zhao, 2001. Reprinted with permission. Figure 11.5. Changes in orientation of azobenzene mesogens for two films of azo-SCLCP-grafted SBS, under 500% strain, subjected to repeated cycles of unpolarized UV irradiation for orientation loss and unpolarized visible irradiation for orientation recovery. Source Bai and Zhao, 2001. Reprinted with permission.
ITO-coated cell (8- to 10- tm gap) is subjected to holographically induced photopolymerization, grating can be formed with alternating regions of polymer and LC droplets. Figure 11.29 is a schematic illustration of the optical switching mechanism based on the reversible photoisomerization of azobenzene dopant mixed with the LC host (in droplets) as well as the supporting experimental data. [Pg.402]

Fig. 21 Selected regions of the experimental infrared spectra of azobenzene isolated in argon matrices at 15 K (a) shortly after deposition of the equilibrium vapor existing over AB crystals at room temperature (b) after trapping of the AB vapors subjected prior to deposition to broadband visible-UV irradiation bya Hg(Xe) lamp, (c) Spectra of (solid line) and Z (dashed line) azobenzene forms simulated on the basis of the PW91/cc-pVTZ calculations. Reproduced from Ref. 71 with permission from the PCCP Owner Societies. Fig. 21 Selected regions of the experimental infrared spectra of azobenzene isolated in argon matrices at 15 K (a) shortly after deposition of the equilibrium vapor existing over AB crystals at room temperature (b) after trapping of the AB vapors subjected prior to deposition to broadband visible-UV irradiation bya Hg(Xe) lamp, (c) Spectra of (solid line) and Z (dashed line) azobenzene forms simulated on the basis of the PW91/cc-pVTZ calculations. Reproduced from Ref. 71 with permission from the PCCP Owner Societies.
Photoisomerization of azobenzenes has been widely developed as photochromic compounds. Lots of papers sriU appeared in this subject from basic chemisty to applications. Some examples were described. Harada et al., reported the effect of cyclodextrin derivatives bearing photo-isomerized stilbene moiety. Single molecule conductance of E- and Z-4, 4 -(ethane-l,2-diyl)dibenzoic acids (E-l and Z-1) was determined using scanning tunnelling microscopy (STM). The dynamics of photoisomerization of E- and Z-urocanic acids (E- and Z-2) driven by Hg-free... [Pg.106]

Numerous azobenzenes and imines have been used to prepare cyclopalladated ctmiplexes, and the liquid crystal properties of some of die products have been investigated. 1 Cyclometallated derivatives have also been prepared from 2-phenylpyiidines, > 2,6-diphenylpyridine, 6-phenyl bipy. O and 6-(2-thienyl) bipy.509 Other substrates subjected to cyclopalladation include amidines, thio- and selenoamides, ll> l N-phenylsulftmyl glycine, hydroxyquinoline derivatives, the drugs diazepam and prazepam, and PBu 3. Doubly cyclopalladated complexes have been prepared from 1,3-diacetylbenzene dioxime and also from N,N-dialkyl benzene-l,3-dicarbaldimines. The 2D NMR spectra of cyclopalladated 8-methylquinoline and benzo-(h)-quinoline show that a CH bond occupies a fifth coordination position above the square plane.520... [Pg.263]


See other pages where Azobenzenes Subject is mentioned: [Pg.49]    [Pg.13]    [Pg.258]    [Pg.123]    [Pg.176]    [Pg.50]    [Pg.269]    [Pg.500]    [Pg.24]    [Pg.28]    [Pg.348]    [Pg.154]    [Pg.209]    [Pg.1]    [Pg.2]    [Pg.48]    [Pg.216]    [Pg.223]    [Pg.226]    [Pg.370]    [Pg.380]    [Pg.394]    [Pg.528]    [Pg.113]    [Pg.123]    [Pg.126]    [Pg.344]    [Pg.263]    [Pg.228]    [Pg.98]    [Pg.281]   


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Azobenzene

Azobenzenes

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