Redox-Responsive Gel-Sol/Sol-Gel Transition in Poly(acrylic acid) Aqueous Solution Containing Fe(III) Ions Switched by Light

Redox-responsive gel-sol/sol-gel transition in aqueous PAA system containing Fe(III)-citrate complex was realized by switching the redox states of Fe(III)/F(II) ions conjugated with photoreduction and oxidation. This reversible transition can be indicated chromatically by the Fe(III) ions and repeated many times as long as there is sufficient citric acid.