Polyimides azobenzene groups

In recent years, optical dichroism and birefringence based on photo-induced trans-cis-trans isomerization of azobenzene groups has been observed with preoriented liquid-crystalline polymers [31-35] at temperatures above the glass transition temperature, and also with various amorphous polymers at temperatures well below the glass transition temperature. In the case of a polyimide (see Chart 5.7), a quasi-permanent orientation can be induced [36-38]. Here, the azobenzene groups are rather rigidly attached to the backbone and photoisomerization occurs at room temperature, i.e. 325 °C below the glass transition temperature, Tg = 350°C. This behavior is in accordance with the fact that the isomerization quantum yields of azobenzene compounds are very similar in solution and in polymer matrices 0 trans cis) 0,1 and 0(cis trans) 0.5. 

Chart 5.7 Chemical structure of a polyimide bearing pendant azobenzene groups. 

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