Photocontrolled transparent–opaque transition of a thermosensitive homopolymer solution based on an azobenzene–cyclodextrin system

<div><p>A solution displaying photocontrolled transparent–opaque transition was prepared through combination of a thermosensitive polymer, poly(<i>N</i>-(3-ethoxypropyl)acrylamide) (PEPAAm), with α-cyclodextrin (α-CD) and a water-soluble azobenzene compound, Azo-Py<sup>+</sup>. α-CD increased the cloud point of an aqueous solution of PEPAAm through formation of inclusion complexes between α-CD and the side groups of PEPAAm. After Azo-Py<sup>+</sup> was added, the cloud point of the solution decreased because most of the α-CD formed complexes with Azo-Py<sup>+</sup>. The concentration of free α-CD was changed by photocontrolled inclusion of Azo-Py<sup>+</sup> in α-CD or exclusion of Azo-Py<sup>+</sup> from α-CD, allowing the cloud point of PEPAAm/α-CD/Azo-Py<sup>+</sup> solution to be changed up and down. Consequently, the transparent–opaque transition of this solution was realised by alternating irradiation with UV and visible light at 38°C.</p></div>