Trans-azobenzenes

Azobenzene [103-33-3] M 182.2, m 68", pK 2.48. Ordinary azobenzene is nearly all in the transform. It is partly converted into the cw-form on exposure to light [for isolation see Hartley J Chem Soc 633 1938, and for spectra of cis- and /ran5-azobenzenes, see Winkel and Siebert Chem Ber 74B 6707947]. trans-Azobenzene is obtained by chromatography on alumina using 1 4 benzene/heptane or pet ether, and crystd from EtOH (after refluxing for several hours) or hexane. All operations should be carried out in diffuse red light or in the dark. 

Fujiwara, M., Chidiwa, T., Tokunaga, R. and Tanimoto, Y. (1998) Crystal growth of trans-azobenzene in a magnetic field of 80kOe. J. Phys. Chem. B, 108, 3417-3419. 

The amphipathic compounds shown in Scheme 2 can form a disc-like micelle(7). The shape of a molecular aggregate depends on the shape of the constituent molecules(8). For instance, conical molecules with large polar head groups prefer to form spherical micelles while cylindrical molecules tend to give flat aggregates. Trans-azobenzene is a rod-like molecule whereas the cis-form is bent. 

A. W. Adamson, A. Vogler, H. Kunkely, R. Wachter. Photocalorimetry. Enthalpies of Photolysis of trans-Azobenzene, Ferrioxalate and Cobaltioxalate Ions, Chromium Hexacarbonyl, and Dirhenium Decacarbonyl. J. Am. Chem. Soc. 1978, 100, 1298-1300. 

F. W. Schulze, H. J. Petrick, H. K. Cammenga, H. Z. Klinge. Thermodynamic Properties of the Structural Analogues Benzo[c]cinnoline, trans-Azobenzene and cis-Azobenzene. Z. Phys. Chem. 1977, 107, 1-19. 

The 1,2,3-diazasilacyclopentane (229) is formed in a photochemical reaction between trans azobenzene and hexamethylsilacyclopropane (Equation (18)) <840M579>. 1,3,4-Diazasilacyclopentane (230) is formed in a formally analogous manner (Scheme 24) in high yields <930M529>. The much... 

TRPES has been recently reviewed and details of the experimental method and its interpretation can be found elsewhere [5], Trans-azobenzene was introduced via a helium supersonic molecular beam into the interaction region of a magnetic bottle photoelectron spectrometer. The molecules were photoexcited by a tunable femtosecond laser pulse (pump pulse) with a wavelength of 280-350nm. After a variable time delay, the excited molecules were ionized by a second femtosecond laser pulse (probe pulse) with a wavelength of 200 or 207nm. The emitted photoelectrons were collected as a function of pump-probe time delay and electron kinetic energy. 

The incorporation of a cationic azobenzene derivative, p-( a> -dimethyl-ethanolammonioethoxyj-azobenzene bromide, into nanoporous silica films and the photochemical reactions of the adsorbed dye were investigated. The nanoporous silica films were prepared from tetramethoxysilane and octadecyltrimethyl-ammonium chloride by the rapid solvent evaporation method which we have reported previously. The adsorption of the cationic azo dye was conducted by casting an ethanol solution of the dye onto the nanoporous silica films. Upon UV light irradiation, trans-azobenzene isomerized photochemically to the c/s-form and photochemically formed c/ s-form turned back to the frans-form upon visible light irradiation. The nanoporous silica films were proved to be an excellent reaction media to immobilize organic photocromic species. 

Here, it is worthwhile to note the difference in the response times of the dissolution and phase separation processes. This is important from the view point of energy conversion efficiency. At 19.5 °C, which is very close to Tc of the polymer solution with all trans azobenzene chromophores, the isomerization of a small number of chromophores, in other words, a small number of photons, was enough to raise Tc above 19.5 °C. Therefore, the transmittance increase took place immediately by irradiation for a very short time. The polymer chain was efficiently expanded by a small number of photons. 

In this rotaxane, a-CD exists at the trans-azobenzene part but it moves to the methylene part when the trans-azobenzene unit is converted into cts-azoben-zene. This light-driven locational change was regarded as a molecular shuttle system. 

Scheme S Semisynthetic method for the cleavage of phospholipase A2 and the reconstitution of azobenzene-modified phospholipase A2. Acm = acetamide, Amd = s-amidinated, DCC = dicyclohexylcarboxiimide, HOSu = N-hydroxysuccinimide, TFA = trifluoroacetic acid, Xaa = trans-azobenzene phenylalanine.

Monolayers representing two-dimensional arrays of membrane-mimetic assemblies, consisting of azobenzene (poly-L-lysine) with 43 % loading of the photoisomerizable units, were prepared.1441 The compressed trans-azobenzene polymer mono-layer exhibited a surface pressure of 7 mN m 1, whereas photoisomerization of the monolayer to the cis-azobenzene state by UV light decreased the surface pressure to... 

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