pH-responsive polymer-supported pyrene-based fluorescent dyes for CO₂ detection in aqueous environments

Detecting fluctuations in carbon dioxide by switching ‘ON’ or ‘OFF’ fluorescence in aqueous environments has often been targeted for efficient monitoring. This switch needs to occur in a drastic and fast way that is visually observable to be effective. CO₂ dissolves in water, leading to a reduction in pH, which can be used to trigger a response. Specifically, the modification of fluorescent dyes with pH-responsive units could create a dye that responds to CO₂ and switches ‘off’ fluorescence. Here, we developed a water-soluble polymer functionalized with a CO₂-responsive pyrene dye. This functional dye contains a tertiary amine conjugated to the aromatic pyrene, which can be protonated at pH ∼ 6.5 or lower. After only 15 s of CO₂ bubbling, a significant fluorescence ‘OFF’ response was observed, with a drastic reduction in fluorescence at 480 nm as a consequence of disrupting non-covalent excimer bonds. Moreover, the exposure to atmospheric air results in a recovery of the excimer state and, therefore, the fluorescence, demonstrating its reversible nature.