The pH variation during a series of photochemical reactions was investigated (Figure ). Firstly, under a nitrogen atmosphere, in the absence of CO2 and carbonate species, the pH of the standard solution decreased from 4.1 to 3.2 within 15 minutes of blue light irradiation (Figure , top). Notably, despite the ultra-short half-life (9 ns) of the excited state, a significant drop in bulk pH was observed. Although further investigations are warranted, it is hypothesized that the solvation by water molecules contributes to the pH change in this high pyranine concentration solution. Secondly, a pyranine solution with an initial pH of 7 was subjected to irradiation, and the pH dynamics were monitored (Figure , middle). A modest pH change from 7.1 to 7.05 was observed during the first 6 minutes of light exposure. This subtle pH variation can be attributed to the buffering effect provided by the ground state of pyranine (pKa 7.7). Thirdly, during the CO2 release and capture step of the standard solution, the pH profile was recorded (Figure , bottom).