Durable Light-Driven pH Switch for CO2 Capture/Release Enabled by Tuning Solvation Environment of Photoacids

Photoacids are organic molecules that release protons under illumination, providing spatiotemporal control of pH. Such light-driven pH switches offer the ability to cyclically alter the pH of the medium and are highly attractive for a wide variety of applications, including CO2 capture. Although photoacids such as protonated merocyanine can enable fully reversible pH cycling in water, they have a limited chemical stability against hydrolysis (<24 hours). Moreover, these photoacids have low solubility and provide only a small pH-jump. In this work we introduce a simple pathway to dramatically increase stability and solubility of photoacids by tuning their solvation environment in binary solvent mixtures. We show that a preferential solvation of merocyanine by aprotic solvent molecules results in a 60% increase in pH modulation magnitude when compared to the behavior in pure water and can withstand stable cycling for > 350 hours. Our results suggest that a very high stability of merocyanine photoacids can be achieved in the right solvent mixtures, offering a way to bypass complex structural modifications of photoacid molecules and serving as the key milestone towards their application in a photo-driven CO2 capture process.