Photo-Modulated Proton Transport in Merocyanine Metastable-State Photoacid Based Polymers

We demonstrate here that light can be used to modulate proton transport in polymeric soft materials using a polymerizable molecular photoswitch. To this end, we design a merocyanine metastable-state photoacid, which we use as a building block to prepare a series of light-responsive polymers. We confirm the metastable character of the proposed monomer, and we elucidate its potential energy surface and the energies associated with its photoisomerization using quantum mechanical calculations. Interestingly, we found that when incorporated into a polymeric matrix, a photoacid loading effect impacts its photochromism and induces significant changes to the polymer nanostructure. Light stimulation of the films results in a reversible decrease in conductivity as the merocyanine simultaneously changes its net charge and functions as a photoacid by releasing protons, effecting switching as well as imparting proton conductivity to otherwise insulating polymers. We further exploit the commensurate changes to the polymer nanostructure to fabricate a light-driven hydrogel actuator. Our work establishes a versatile synthetic platform for the design of photo-modulated proton-conductive systems, offering new opportunities for responsive materials and iontronics applications.