Chemomechanical Systems Based on Steric Photo-Isomerization

4 Chemomechanical Systems Based on Steric Photo-Isomerization 

Aromatic polyimides containing an azobenzene in the chain backbone (4,4-di-aminoazobenzenepyromellitamide) showed reversible photo and thermal contraction. The effect was associated with trans cis isomerization However, the length changes was not large (0.23 % contraction after 300 min irradiation with UV at 200 °C) and had a half-life of contraction of about 40 min. 

Attempts of photo-dilatation and contraction of polyamide and polyimide containing stilbene in the aromatic chain backbone were made in water. It was found that poly-imide-poly(iininoisophthaloylimino-l, 3-phenylenevinylene-1,4-phenylene), if stretched under constant tension, relaxed on irradiating with UV light, and recovered to initial stress when the irradiation was stopped This type of polyimide is stable in the dark in the trans conformation which is more stretched, and transforms to the cis form which is the more coiled conformation under irradiation. Therefore, the relaxation by photoirradiation should be associated with an increase in polarity of the polymer film. 

Shinohara and Sakurai synthesized polymers containing photochromic pendant groups such as azobenzene or spiropyrane and observed the photo-induced change in 

Azobenzene derivatives can be used as photoantennas because of their large geometrical changes and good reproducibility, and several groups have attempted the photocontrol of chemical and physical functions of membranes emulsions polymers and cyclodextrins 

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