Stimuli-responsive polymers. 9. Photo-regulation of optical rotations in chiral polyesters: Altering responsive outputs with conformationally flexible backbone elements

Conformationally restricted polyesters comprising alternating azobenzene and chiral binaphthylene main-chain units undergo photo-induced oscillations in optical rotatory power when stimulated with sequential intervals of ultraviolet and visible light exposure. The incorporation of flexible (oligo)ethylene oxide backbone segments into these constructs has resulted in a new family of materials having vastly altered photo-responsive chiroptical properties. Light-regulated outputs were found to be strongly dependent upon the length of the flexible backbone segments employed and on their specific locations of placement within the polyester chain. Most notably, the insertion of flexible oligo(ethylene oxide) spacer elements between neighboring binaphthylene and azobenzene main-chain units had a pronounced damping effect on the photo-dynamic behavior exhibited by these chiral systems. Similar results were noted for a related series of oligomeric model compounds that were specifically designed to mimic local monomer sequences present within the larger polyester structures.