Azobenzene photochemistry

A bulk azo sample or solution under illumination will achieve a photosta-tionary state, with a steady-state trans-cis composition based on the competing 

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To add to the confusion, various groups reported that gas-phase photolysis of phenyl azide produced the absorption and emission spectra of triplet phenylni-trene. " These observations were reconciled by the work of Leyva et al. who discovered that the photochemistry of phenyl azide in the presence of diethylamine was very sensitive to temperature. Above 200 K, azepine 30 is formed, but <160 K, azobenzene, the product of triplet nitrene dimerization, is produced. The ketenimine can react with itself or with phenyl azide to produce a polymer, which can be converted into an electrically conducting material. Gritsan and Pritchina pointed out that at high-dilution ketenimine 30 can interconvert with singlet phenylnitrene which eventually relaxes to the lower energy triplet that subsequently dimerizes to form azobenzene. 

Rotational Raman spectra of N2 and O2 Resonance fluorescence spectrum of Br2 Vibrational-rotational spectra of CD3H and CH3D Spectrophotometric study of stabihty of metal ion-EDTA complexes Kinetics of the H2 + I2 = 2HI reaction in the gas phase Weak-acid catalysis of BH4 decomposition Photochemistry of the cis-trans azobenzene interconversion Isotope effect on reaction-rate corrstants... 

In the experimental realm, picosecond and femtosecond experiments contribute to the understanding of isomerization. A review of the ultrafast dynamics of photochromic systems appeared in 2000. A study of the photochemistry of E-azobenzene on excitation of the S2 state [ (71,71 )] was... 

Hamai, S., and Hirayama, F. (1984). S2 —> Sg fluorescence of azobenzene. Book of Abstracts, Annual Symposium cm Photochemistry (Japan), 315-316. 

Polarized light absorption orients both isomers of photisomerizahle chromo-phores, and quantified photo-orientation both reveals the symmetrical nature of the isomers photochemical transitions and shows how chromophores move upon isomerization. Photo-orientation theory has matured by merging optics and photochemistry, and it now provides analytical means for powerful characterization of photo-orientation by photoisomerization. In azobenzenes, it was found that the photochemical quantum yields and the rate of the cis—>trans thermal isomerization strongly influence photo-... 

Song, X., Geiger, C., Vaday, S., Perlstein, J., and Whitten, D. G., Supramolecular Aggregates of Photoreactive Aromatics. Structure, Photophysics and Photochemistry of Stilbene and Azobenzene Phospholipids. J. Photochem. PhotobioL A Chem. 102, 39 (1996). 

I. Mita, K. Hone, and K. Hirao, Photochemistry in polymer solids. 9. Photoisomerization of azobenzene in a polycarbonate film, Macromolecules 22, 558-563 (1989). 

Cattaneo, P., Persico, M., An Ab Initio Study of the Photochemistry of Azobenzene, Phys. Chem. Chem. Phys. 1999, 1, 4739 4743. 

New photoresponsive polymers and peptides have been developed by incorporation of an azobenzene chromophore. The photochemistry of azobenzene-containing polymers has been reviewed,and the ion-conducting polymer composite film of poly(vinyl chloride)/the azobenzene liquid crystal (4)/lithium perchlorate is a promising material for use in photoinduced image storage.Photoisomerization has also been demonstrated... 

A very large increase in kjsc is observed with para-meth-oxy and -dimethylamino substituents (Table 5.7). This result is consistent with the solution phase photochemistry of para-methoxy and para-dimethylaminophenyl azides, which largely yield azobenzenes on photolysis. 

One feature of the data in Table 1.1 is that and <1)z, e do not add up to unity. This is an indication that more than one potential surface is involved in the isomerization mechanism (see Section 1.6). The most unusual fact disclosed in Table 1.1, however, is that the quantum yields are wavelength dependent. (])e +z about twice as large for low-energy excitation of the (n,n ) state as it is for high-energy excitation of the (Jt,rt ) state. Obviously, for azobenzenes Kasha s rule—that fluorescence and photochemistry take... 

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