A colorimetric and fluorescent chemosensor for the highly sensitive detection of CO2 gas: experiment and DFT calculation

[Display omitted] •A squaraine-based system was developed to fluorescently and colorimetrically sense CO2 gas with high sensitivity.•A plausible mechanism that the deprotonated SQ-NH2 with fluoride ion will rapidly restore on condition that acidic carbon dioxide gas bubbles is proposed.•Allowing colorimetric and fluorescent visualizing the presence of CO2 gas. A squaraine-based system was developed and demonstrated to fluorescently and colorimetrically sense CO2 gas with high sensitivity in DMSO in the presence of fluoride ion. From results, large hypsochromic shifts were observed both in the absorption spectra (134nm) and fluorescence spectra (126nm), and the color change of solution could be clearly observed by the naked eye in response to carbon dioxide gas. Combining 1H NMR titration tests and theoretical calculations, a plausible sensing mechanism that the deprotonated SQ-NH2 with fluoride ion will rapidly restore on condition that acidic carbon dioxide gas bubbles in DMSO is proposed and further revealed. Moreover, theoretical studies agree with experimental data well.