Light-triggered reversible solubility of α-cyclodextrin and azobenzene moiety complexes in PDMAA-co-PAPA via molecular recognition

Photoresponsive polymer with azobenzene pendant group (PDMAA-co-PAPA) was synthesized by radical polymerization of NN-dimethylacrylamide (DMAA) and N-4-phenylazophenyl acrylamide (PAPA), and the characterization of the inclusion complexes of the PDMAA-co-PAPA with alpha-cyclodextrin (alpha-CD) were performed by FTIR, GPC, H-1 NMR, 2D NOESY, and UV-vis spectroscopy. It was found that the solubility of PDMAA-co-PAPA and alpha-CD inclusion complexes in aqueous solution showed tunable property, which could be triggered by alternating UV-vis light irradiation at a certain temperature due to the effect of molecular recognition of alpha-CD with azobenzene moiety in the polymer. After UV irradiation, the lower critical solution temperature (LCST) of the polymer aqueous solution increased slightly without (alpha-CD while the LCST decreased sharply at presence of alpha-CD. Furthermore, UV spectroscopy showed that the photoisomerization of the polymer solution went on rapidly and reversibly, and 2D NOESY data suggested that the inclusion complexation of alpha-CD with trans azobenzene moiety and the decomplexation with cis azobenzene resulted in reversible solubility behavior when objected to UV and Vis light irradiation alternately. (c) 2007 Wiley Periodicals, Inc.