To generate a high-concentration aqueous solution of the photoacid for gas output, we employed pyranine, 26,28-30 a well-established hydrophilic photoswitch with a maximum solubility of 520 mM in water (Figure ). Pyranine has been extensively studied as a photoacid in various research fields, including sensors, biology, and optics . Its ground state pKa is 7.7, while the excited state pKa* is 0.6 , aligning well with our design and the pH of the bicarbonate buffer under 15% CO2. As the excited state of pyranine has a relatively short half-life of 9 ns 28 , no significant accumulation of excited states in the bulk solution is expected using the limited power of a commercial LED light source. However, we hypothesized that at a local time scale, localized concentrations could lead to the generation of CO2 gas output. Once CO2 gas escapes from the solution, the total dissolved inorganic carbon (DIC) content will gradually decrease over time.