Electrochemically switched systems have been reported that depend on the reversible generation of hydroxide and corresponding pH swing in the alkaline direction. Solutions containing redox-active bases, such as phenazines, have been shown to undergo large pH increases upon reduction, enabling separation of CO2 from very dilute streams. A major limitation of electrochemical strategies is the oxygen-instability of many reduced species in aqueous solution, although promising progress has been made using alcohol additives in organic solvent. We postulated that a photoswitchable base could in principle achieve similar cyclic pH swings in aqueous solution without the problems of oxygen sensitivity nor the requirement for electrochemical apparatus such as cells, membranes, electrodes, and supporting electrolytes. However, while metastable-state photoacids such as merocyanines have been continuously optimized over the past decades, and extensive physical-organic studies have been performed on their use as photoswitchable buffers, analogous research on switchable photobases is rather limited. Several Brønsted photobases, mainly consisting of quinolines and acridines, have been discovered, and Lukas et al. showed a guanidine Brønsted photobase could form reversible adducts with CO2 in acetonitrile solution using light.