Polymers with azobenzene groups

Azobenzene is the most frequently used chromophore. It undergoes isomerization from the trans- to the c/5-form under ultraviolet (UV) irradiation (300 > > 400 nm) the c -form can return thermally or photochemically to the trans-foxm. Table 1 summarizes several examples of photoresponsive polymers with azobenzene groups. 

Butcher and Cotter (1990), Boyd (2003) and Sutherland (2003) provide overviews of non-linear optics. Prasad and Williams (1991) have discussed the non-linear optics of molecules and polymers. Detailed accounts on this topic can be found in Bosshard et al. (1995), Kajzar and Swalen (1996) and Kuzyk and Dirk (1998). More specialised reviews are those of Yesodha et al. (2004), on non-linear polymers with azobenzene pendent groups, and Sioncke et al. (2003), who describe the second order non-linear optical properties of chiral molecules and polymers. 

Polyamides with azobenzene groups in the backbone are among the earliest in which trans-cis isomerizable chromophores were used to regulate the polymer conformation [13, 14]. The intrinsic viscosity [q] of polyamide (6) in polar AJV-dimethyl-acetamide was found to decrease from 1.22 to 0.5 dl/g upon ultraviolet irradiation... 

It is known that a free surface is required for SRG formation. An azobenzene-containing polymer surface covered with a 25 nm-thick non-photoactive layer seems to be sufficient to fully suppress SRG formation [96], Here, we demonstrate that polymers with azobenzene moieties as side-groups and terminal perfluoroalkyl chains can efficiently suppress SRG formation in a similar manner. 

Yaroschuk O, et al. 2001. Light induced structures in liquid crystalline side chain polymers with azobenzene functional groups. J Chem Phys 114(12) 5330 5337. 

Irie et al. [217] synthesized a number of polyamides with azobenzene groups in the backbone. All the polymers exhibit photo-viscosity effects. In solutimis in VA/ -dimethylacetamide, a 60% reduction in specific viscosity can be achieved by UV hght irradiation (410 > A > 350 nm). The initial viscosity is regained by storage in the dark at room temperature for 30 h. 

Yaroschuk, O., Setgan, T., Lindau, J., Lee, S.N., Kelly, J., Chien, L.C. Light induced structures in liquid crystalline side-chain polymers with azobenzene functional groups. J. CJiem. Phys. 114(12), 5330-5337 (2001)... 

Concerning the polymers, Irie and collaborators prepared a number of polyamides with azobenzene groups in the backbone (e.g., 21). The viscosity of the polyamides in a polar solvent decreased upon irradiation and returned to the initial value in the dark. 

This paper summarizes the theoretical analysis of some new molecules with methylsulfonyl group as the electron acceptor group, describes the syntheses of new stilbene and azobenzene systems, and presents the measurements of their optical spectra, ground-state dipole-moments, and molecular hyperpolarizability coefficients, p. We compare theoretical and experimental results and comment on the potential usefulness of these chromophores as components for NLO materials. The incorporation of sulfonyl-containing chromophores into polymers, and the NLO properties of the resulting materials, will be discussed in our forthcoming paper (9). 

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