The application of merocyanine photoacids has been previously largely limited to neutral and acidic pH values. Here we introduce a new merocyanine photoacid with superior pH switching qualities. By increasing the pK a in the dark (pK a dark ) and the solubility we increased the reversible visible light induced pH jump to 3.5 units. Moreover, it is the first demonstration of a merocyanine photoacid able to generate a significant pH drop from a basic (pH 8.3) to an acidic (pH 5.2) environment.