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

The reversible photoisomerization and the thermal isomerization of azobenzene-based (Az.b.) groups covalently bound to (meth)acrylic (co)polymers were investigated in thin films. For the amorphous polymers it was found that a broad range of the thermal cis --> trans isomerization rates could be obtained by varying the substituent, spacer, and copolymer composition. The liquid crystalline (LC) polymers showed an interesting behavior of the orientation of the stable trans state when exposed to visible light, during which the orientation of the Az.b. groups changed from more or less random to more perpendicular (photoselection process). This change of orientation of the Az.b. groups may be suitable for optical data storage. In principle, the orientation change is permanent, but it can be easily erased by heating the LC polymer above its isotropization temperature, on which the original random orientation is largely restored.