Light-Controlled Lyotropic Liquid Crystallinity of Polyaspartates Exploited as Photo-Switchable Alignment Medium.

Two polyaspartates bearing -fluorinated azobenzenes (FAB) as photo-responsive groups in the side chain were synthesized: PFABLA () and co-polyaspartate PpFABLA--PBLA [, 75%(n/n) PFABLA content]. As a consequence of the /-isomerization of the side chain, PFABLA () undergoes a visible-light-induced reversible coil-helix transition in solution: Green light (525 nm) affords the coil, and violet light (400 nm) affords the helix. FAB significantly increases the thermal stability of the -isomer at 20 °C ( = 66 d for the -isomer) and effectively counters the favored back formation of the helix.