The transfer of protons lies at the core of numerous biological and chemical processes. Herein we propose a visible-light triggered molecular system that allows to reversibly tailor acidity and, additionally, fluorescence. This robust bi-functional system opens up the doors for novel studies on acid-mediated processes by incorporating fluorescence. The two photosensitive compounds used for this study, a Metastable-state Photoacids (mPAH) and a boron-dipyrromethene (BODIPY) derivative, allow for consistent modulation of both fluorescence and pH over multiple cycles.