Building upon this concept, we have developed a parallel scheme for photochemical modulation of organic molecular photoswitches (Figure ). In this scheme, the resting-state photoswitch, when kept in the dark along with a suitable absorbent (e.g., carbonate, amine, or alkaline solution), captures CO2 from the diluted source. Upon irradiation, the CO2-saturated solution releases concentrated CO2 by lowering the local pH through the decreased pKa* of the excited states of the photoswitch. By blocking the light and returning to the dark, the excited states of the photoswitch revert to the ground state, effectively closing the cycle. In designing photo-swing carbon capture by photochemical modulation of photoswitches, we used a visible light photoacid and bicarbonate buffered system as an absorbent in this work (Figure ). The relationship between the bicarbonate buffer solution pH and pKa of the ground state and excited state of photoacid is important in the design of an efficient system. The pKa of the ground state is desired to be higher than the pH of the CO2 saturated solution, and therefore, most photoacid remains protonated under dark conditions, while the pKa* of the excited state is desired to be lower than the pH of the CO2 saturated solution so that the photoacid generates protons upon irradiation to release CO2 out of the solution. During the CO2 release step, the excited photoacid would be deprotonated and bicarbonate decomposed to CO2 and water under the decreased pH of the local condition. Following the CO2 capture step, the photoacid returns back to its ground state and takes up a proton back under dark conditions. Following release of CO2 during irradiation, with subsequent reversion of the buffer bicarbonate to carbonate ions under dark conditions, the sorbent is primed to again capture CO2 from the dilute source.