Photoactivity, reversibility, and stability of a merocyanine-type photoacid in polymer films

Over the past years, merocyanine type photoacids have been used for the development of various visible-light responsive polymers and polymer sensors. However, the physicochemical behavior of this type of photoacid in polymers has not been studied previously. In this work, the photoactivity, reversibility, and stability of a merocyanine-type photoacid in polymer films are investigated. Polymer films doped with the photoacid were found to be stable under ambient conditions over half a year. Kinetics of the reaction is complicated for both the forward and backward process due to slow proton diffusion in the polymer. Improving proton transfer by addition of ammonium trifluoromethanesulfonate enhances the reverse reaction rate. The photoacid-doped polymer showed good photostability upon a test of 100 cycles of irradiation and recovery in the dark.