Harnessing light energy for sustainable energy conversion is a key challenge in developing next-generation energy technologies. In this work, we introduce a molecular-switch approach based on merocyanine photoacids to create and control proton gradients in aqueous environments. By tuning the solvation environment in water–methanol mixtures, these switches produce substantial, reversible changes in acidity, generating proton concentration gradients of up to 4 pH units under 500 nm irradiation. This controlled, light-triggered proton transfer can be coupled to an electrochemical readout, delivering stable open-circuit voltages up to 240 mV.
More broadly, this platform establishes a route to photo-responsive proton-gradient control without committing to a specific device concept. The ability to modulate proton activity with molecular-level precision provides a useful analogue to biological energy transduction and offers a versatile basis for integrating photoacids into functional architectures. These findings highlight opportunities for developing responsive materials and interfaces that translate light inputs into programmable chemical and electrical outputs, with relevance to artificial molecular systems and related energy-conversion strategies.