PHOTORESPONSIVE BEHAVIOR OF AZOBENZENE-BASED (METH)ACRYLIC (CO)POLYMERS IN THIN-FILMS

The reversible photoisomerization and the thermal isomerization of azo benzene-based (Az.b.) groups covalently bound to (meth)acrylic (co)pol ymers were investigated in thin films. For the amorphous polymers it w as found that a broad range of the thermal cis --> trans isomerization rates could be obtained by varying the substituent, spacer, and copol ymer composition. The liquid crystalline (LC) polymers showed an inter esting behavior of the orientation of the stable trans state when expo sed to visible light, during which the orientation of the Az.b. groups changed from more or less random to more perpendicular (photoselectio n process). This change of orientation of the Az.b. groups may be suit able for optical data storage. In principle, the orientation change is permanent, but it can be easily erased by heating the LC polymer abov e its isotropization temperature, on which the original random orienta tion is largely restored.