Photochromic azobenzenes

T. Ikeda, T. Miyamoto, S. Kurihara, and S. Tazuke, Effect of structure of photoresponsive molecules on photochemical phase transition of liquid crystals. IV. Photochemical phase transition behavior of photochromic azobenzene guest/polymer liquid crystal host mixtures, Mol. Cryst. Liq. Cryst. 188, 223-233 (1990). 

Y. Kawanishi, T. Tamaki, T. Seki, M. Sakuragi, Y. Suzuki, and K. Ichimura, Multifarious liquid crystalline textures formed on a photochromic azobenzene polymer film, Langmuir 7,1314-1315 (1991). 

Structure and Segmental Mobility of Polyester Urethanes Using Photochromic Azobenzene Probes... 

This chapter discusses photochromic azobenzene polymers and photochromic molecules capable of undergoing photodimerization as materials for potential use in optical data storage applications. A brief introduction to photochromism, including recent examples of some photochromic systems, other than azobenzenes, based on variety of applications is presented at the outset. Thereafter, we shall focus on azobenzene photoaddressable polymers (PAPs) and [4 + 4]-photocycloaddition as materials for ultrahigh capacity optical data storage. 

We shall now embark on the main focus of this chapter photochromic azobenzene polymers and photochromic materials capable of undergoing photodimerization for potential use in optical data storage applications. Herein, the photochromic polymers described are those in which the photochromic molecule is covalently linked, either as part of the main chain or as a side-chain, to the polymeric system. 

A PAP may be either amorphous or liquid crystalline and usually comprises suitably functionalized photochromic azobenzene and mesogenic moieties as side groups. The latter play an important cooperative or synergistic role with the photo-chromic group enhancing the overall birefringence (photoinduced anisotropy). 

The effect of a combination of photochromic azobenzene with mesogenic units within the same polymer on cooperative motion and anisotropic enhancement is exemplified by the CPI and K1 polymer systems of Zilker et al. [53] shown in Fig. 6.16. In the CPI-50 polymer, a clear distinction between chromophore and cooperative mesogen (CPI-50 polymer) existed. There was no apparent distinction between chromophore and mesogen in the Kl-40 polymer because mesogen also contained a photoactive azo linkage. The boundary between fast-chromophore and slow-mesogen reorientation is blurred and an effective enhancement of reorientation occurs. 

K. Huang, H. Qiu, and M. Wan, Synthesis of highly conducting polyaniline with photochromic azobenzene side groups, Macromolecules, 35, 8653-8655 (2002). 

Rau H, Roettger D. 1994. Photochromic azobenzenes which are stable in the trans and cis forms. Mol Cryst Liq Cryst Sci Technol, A 246 143 146. 

Willner I, Rubin S, Zor T. 1991b. Photoregulation of alpha chymotrypsin by its immobi lization in a photochromic azobenzene copolymer. J Am Chem Soc 113(10) 4013 4014. 

Ruslim C, Ichimura K. 2000. Conformational effect on macroscopic chirality modification of cholesteric mesophases by photochromic azobenzene dopants. J Phys Chem B 104(28) 6529 6535. 

Wang, G. Zhang, M. Yang, Q. Liu, R Cheng, Z. Guo, R. Yang, H. Photoinduced phase transitions in chiral hinaphthyl-diol-doped smectic liquid crystals by a photochromic azobenzene. Chem. Lett. 2010, 39, 1144—1145. 

The majority of the published papers, reviews, and several books are related to the photochromic azobenzene-containing LC polymers. Under polarized UV-light exposure. 

Liao, L-X., Stellacci, F., and McGrath, D.V. (2004) Photoswitchable flexible and shape-persistent dendrimers comparison of the interplay between a photochromic azobenzene core and dendrimer structure. J. Am. Chem. Soc., 126, 2181-2185. 

Hafiz, HR. and Nakanishi, F. (2003) Photoresponsive liquid crystal display driven by new photochromic azobenzene-based Langmuir-Blodgett films. Nanotechnology, 14, 649-654. 

Loos PF et al (2008) Theoretical investigation of the geometries and UV-vis spectra of poly (L-glutamic acid) featuring a photochromic azobenzene side chain. J Chem Theory Comput 4 637-645... 

Thus, a number of photoresponsive dendrimers with photochromic azobenzene units in the exterior, interior, periphery, or whole of the structure have been designed and prepared with different intentions. 

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