Photoreorientation, azobenzenes

FIG. 6.25 Schematic representation of azobenzene photoreorientation by repeated photoisomerization upon irradiation with polarized tight. 

In polyurethane 33, the azobenzene moieties are separated from each other along the polymer backbone by isophorone units and have the free volume necessary for isomerization and molecular reorientation. This polymer s azobenzene moieties can be photoisomerized readily in mixed LBK films, as demonstrated by measuring the optically induced birefringence that originates from the photoreorientation of the chromophore upon polarized irradiation see Section 6.5.2). 

Photoreorientation of azobenzene chromophores by irradiation with polarized light is a very important photoinduced structural change. For azobenzene moieties, there is a widely accepted mechanism for the photo-reorientation The azobenzene moieties that are parallel with their long axis (and therefore with their transition dipole) to the electric field vector... 

The role of the supramolecular order of LBK films on the photoreorientation of azobenzene moieties upon polarized irradiation was investigated in detail. It was found that the photo(re)orientation proceeds reaclily in disordered, spin-coated films of azobenzene polymer 34 or azobenzene-containing polypeptide 38, whereas the photoreorientation is hindered in highly ordered LBK films of these polymers. In the case of polyacrylaerylat 34 and polypeptides 38 with shorter spacers (n = 2), the photoreorientation proceeds readily after the structure of the LBK film has been randomized by UV irradi-... 

Thus, potential application of the ISA complexes for optical data storage has also been demonstrated. Photoreorientation of the induced optical structures in the complexes has been successfully achieved. Well-defined optical patterns were obtained when a second irradiation was applied through a standard photomask (Fig. 2.12c,d). Induction of optical phase gratings in films of the azobenzene-containing ISA complexes was also observed. A diffraction efficiency (DE) of approximately 7% was obtained on 100-nm thick films (calculated value of An that corresponds to this efficiency is 0.54) of the EO-FCigD complex after irradiation with two circularly polarized interfering beams of an Ar laser. 

Schdnhoff, M., Mertesdorf, M., Losche, M. Mechanism of photoreorientation of azobenzene dyes in molecular films. J. Phys. Chem. 100(18), 7558-7565 (1996)... 

Warner M, Terentjev EM (2003) Liquid crystal elastomers. Oxford University Press, Oxford Wolarz E, Eischer TH, Stumpe J (2005) Photoreorientation in liquid crystalline side-group polysiloxane with azobenzene derivative admixture. Mol Cryst Liq Cryst 437 1245-1253 Wu H, Zhang L, Xu Y, Ma Z, Shen Z, Fan X, Zhou Q (2012) Amphiphilic mesogen-jacketed liquid... 

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