Azobenzene doped polymers

Wang, Y., Zhao, J., Si, J., Ye, P., Fu, X., Qiu, L., and Shen, Y. (1995). Dynamic studies of degenerate four-wave-mixing in an azobenzene-doped polymer film with an optical pump. /. Chem. Phys. 103, 5357-5361. 

Srikhirin, X, Laschitsch, A., Neher, D., and johannsmann, D. Light-induced softening of azobenzene dye-doped polymer films probed with quartz crystal resonators. Appl. Phys. Lett. 2000, 77, pp. 963-965. 

One disadvantage of azobenzene molecules is the slow and unavoidable thermal relaxation from the cis to trans isomer, which gives rise to the problem of lacking longterm stability or slow restoration rate. White et al. found that polymer stabilization could dramatically fasten the thermal relaxation of azobenzene-doped CLCs [35]. The polymer-stabilized CLC relaxed to the initial stage from the isotropic state in 2 h compared to 72 h required for the relaxation of CLC without polymer stabilization. 

One of the drawbacks of doping polymer matrices with azobenzenes that exhibit photoinduced motions is that at higher concentration levels, phase separation... 

Fleischmann EK, Zentel R (2013) Liquid-crystalline ordering as a concept in materials science from semiconductors to stimuli-responsive devices. Angew Chem Int Ed 52 8810-8827 Garcia-Amoros J, Velasco D (2014) Understanding the fast thermal isomerisation of azophenols in glassy and liquid-crystalline polymers. Phys Chem Chem Phys 16 3108-3114 Garcia-Amoros J, Szymezyk A, Velasco D (2009) Nematic-to-isotropic photo-induced phase transition in azobenzene-doped low-molar liquid crystals. Phys Chem Chem Phys 11 4244-4250... 

The azochromophore must be covalently attached to the polymer chain (either as a side chain or in the main chain). Attempts to produce SRGs with guest-host systems led to very small surface modulations about 15 nm or less)." Though photoisomerization can be induced in these systems, efficient SRG formation is not possible, probably because the polymer chains are not induced to move unless covalently attached. However, SRG formation of a doped system in which the polymer also contained an azobenzene unit has also been studied (see Section 14.4.4). The much less efficient inscription... 

C. Barret, A. Natansohn, and P. Rochon, Cis-trans thermal isomerization rates of bound and doped azobenzenes in a series of polymers, Chem. Mater. 7, 899-903 (1995). 

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