Stimuli-responsive polymers. 10. Photo-regulation of optical rotations in azobenzene modified poly(ester-amide)s containing highly structured, atropisomeric backbone geometries.

The chiral atropisomeric monomer R-(+)-2-amino-1,1'-binaphthalen-2-ol provides convenient access to a number of azobenzene modified poly(ester-amide)s having highly-ordered main-chain arrangements of their constituent monomer groups. When evaluated in dilute solution environments, each of the polymers that contain the azobenzene stimuliphore undergo photo-induced oscillations in optical rotatory power when stimulated by multiple UV light-visible light illumination cycles. Polymer behavior is strongly influenced by the particular sequence of monomer units positioned along the chiral ester-amide backbone. Periodic variants that are fashioned from R-binaphthylene, azobenzene and para-phenylene segments exhibit particularly interesting response profiles. In certain cases, their light-modulated chiroptical outputs alternate between two discrete states, fluctuating between positive and negative specific rotations, or reversibly interconverting between optically active and optically inactive endpoints. This chiroptical switching behavior is greatly influenced by the choice of solvent, providing an added means for tuning the binary outputs afforded by these structurally well-defined materials. [ABSTRACT FROM AUTHOR]