Azobenzene-based light-responsive hydrogel system.

TLDR: The experimental results indicate that the trans-azobenzene units are bound strongly within the cavities of 2 whereas the cis-azabenzene is not bound at all.

Abstract: A deoxycholic acid-modified β-cyclodextrin derivative (2) and an azobenzene-branched poly(acrylic acid) copolymer (3) were prepared, and the association and dissociation of 2 with the trans/cis-azobenzene units in 3 were characterized by UV/vis spectroscopy, induced circular dichroism, and 1H NMR spectroscopy. The experimental results indicate that the trans-azobenzene units are bound strongly within the cavities of 2 whereas the cis-azobenzene is not bound at all. A supramolecular inclusion complex (1), formed by 2 and 3, is accompanied by the formation of a hydrogel. The light-responsive gel-to-sol and sol-to-gel phase transitions of the hydrogel, induced by trans-cis photoisomerization of the azobenzene units, were investigated. In the hydrogel system, the trans-azobenzene units in 3 are included inside the hydrophobic cavity of 2. Upon photoirradiation with UV light of 355 nm, the hydrogel is converted efficiently to the sol phase because the trans-azobenzene units are converted photochemically to the...