Azobenzene absorption spectroscopy

A series of aggregation structures of bilayer forming azobenzene amphiphiles, CnAzoCmN+Br, both in single crystals and cast films was determined by the X-ray diffraction method and uv-visible absorption spectroscopy. From the relationship between chemical structures and their two-dimensional supramolecular structure, factors determining the molecular orientation in bilayer structure were discussed. Some unique properties based on two-dimensional molecular ordering were also discussed. 

The mixed liposomal solutions were prepared by the ethanol-injection method(13) in order to obtain completely transparent solutions. It is interesting to note that miscibility of the photochromic amphiphiles with DPPC depend on the position of bulky azobenzene. If azobenzene is incorporated close to the end of long alkyl chain, a stable mixed bilayer state cannot be formed. On the other hand, when the azobenzene moiety is located near the head group or at the center of the hydrocarbon tail, the azobenzene amphiphiles are successfully incorporated into the bilayer membrane. No individual micelle formation nor phase separation in the bilayer was observed at 25 °C by absorption spectroscopy. However, the microstructure of the mixed liposomes depends on the type of azobenzene amphiphiles. 

Lednev, I. K., Ye, T.-Q., Hesteii R., and Moore, J. N. (1996). Femtosecond rime-resolved UV-visible absorption spectroscopy of trans-azobenzene in solution. /. Phys. Chem. 100, 13338-13341. 

Uznanski, P., Kryzsewski, M., and Thulstrup, E. W. Polarized Absorption Spectroscopy of Azobenzene and frans-Stilbene in Stretched Polyethylene Films. Spectrochini- Acta Part A 46, 23 (1990). 

When the potential was scanned to 0 mV, a pair of waves due to the redox of the azobenzene moiety appeared, in addition to that of ferrocene in the first potential scan (sohd line in Fig. 13c). The wave due to the redox of azobenzene, however, disappeared, and the redox potential and the peak separation of the redox wave due to ferrocene became more negative and smaller, respectively, in the second scan (dotted line in Fig. 13c). The redox potential and the peak separation returned to the original values after UV irradiation. These changes in the electrochemical characteristics of the latter electrode were reversible. On the basis of the structural analysis results by in situ Fourier-transform infrared reflection absorption spectroscopy (FT-IRRAS), we concluded that the electrochemical properties, that is, the redox potential and the charge transfer rate, of the ferrocene group in the SAM-modified gold electrode can be reversibly controlled... 

The stability of the induced I phase at the irradiated site of polymer azobenzene LC strongly depends on temperature. At temperatures above the induced I phase disappeared and the N phase was restored after some time, which depended on temperature. At high temperatures such as 140°C, the I phase disappeared in seconds. At temperatures just above Tg the induced I phase remained fairly stable for some time, but disappeared after a prolonged time. On the other hand, at temperature below Tg the induced I phase remained unchanged even after 1 year and 6 months. The cis-trans back-isomerization took place thermally even at room temperature, and the trans-ioun was restored almost completely in 1 day. Polarized absorption spectroscopy showed that even though the trans-iorm was restored in 1 day at room temperature, orientation of the /ra 5-azobenzene mesogens was different from that of the initial state. Before photoirradiation, the azobenzenes were aligned in one direction to form uniaxial monodomain, but after photoirradiation the cw-form was produced, and N—I phase transition was induced. However, after the trans-ioim was restored thermally, the orientation... 

The hetero-dimerization behavior of dye-modified -cyclodextrins with native CDs was investigated by means of absorption and induced circular dichroism spectroscopy in aqueous solution [43], Three types of azo dye-modified /i-CDs show different association behavior, depending on the positional difference and the electronic character of substituent connected to the CD unit in the dye moiety. p-Methyl Red-modified fi-CD (1), which has a 4-(dimethylamino)azobenzene moiety connected to the CD unit at the 4 position by an amido linkage, forms an intramolecular self-complex, inserting the dye moiety in its / -CD cavity (Figure 13). 1 also associates with native a-CD by inserting the dye residue into the a-CD cavity. The association constants for such hetero-dimerization are 198 M"1 at pH 1.00 and 305 M 1 at pH 6.59, which are larger than the association constants of 1 for / -CD (43 M 1 at pH 1.00). 

A photochromic polymer containing azobenzene units has also been prepared by modification of a naturally occurring microbial poly(E-L-lysine) (Scheme 5, Structure IX), and investigated by means of absorption and circular dichroism spectroscopy.1431 The structure of this polymer, however, does not correspond to those of polypeptides, which are poly(amide)s of a-amino acids, and therefore the results cannot be discussed in terms of the typical polypeptide structures (a-helix, P-structure, random coil) and their standard CD spectra. 

Triplet state data for azobenzene-type azo compounds are very limited. Direct absorption of a 0.51 mol solution in C7H15J in 5 cm cells has not been detectable. Neither has phosphorescence been detected. The energy of triplet states has been located only by chemical spectroscopy, i.e., the quenching of other molecules triplet states by azobenzene. Ronayette et found two relevant triplet states at about 196 and 180 kj moH... 

Figure 14b). a-CyD resides at the azobenzene part when it takes the trans-form, while photoisomerization to the dMorm pushes it to one of the methylene chains. CD absorption is always active in 25, but the location of a-CyD dramatically influences the ICD spectral shape. Hence, the shuttle movement of 25 can also be observed by CD spectroscopy. ... 

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