Cholesteryl naphthalimide-based gelators: Their applications in the multiply visual sensing of CO₂ based on an anion-induced strategy

Several cholesteryl naphthalimide-derived compounds have been sythesized and developed as CO₂ sensors. The derivatives, incorporating ether chains, were found to be capable of gelating various organic solvents, due to the modulation of the hydrophilicity/hydrophobility properties of them. The resulting organogels were well characterized by field emission scanning electron microscopy (FE-SEM), FT-IR spectroscopy, concentration- and temperature-dependent ¹H NMR spectra, and powder X-ray diffraction (PXRD). These gelators can be applied as fluorescent sensors for CO₂ in DMSO solutions via the anion-triggered strategy. Furthermore, the resulting organogelation systems in DMSO could also provide visual sensing means for CO₂ via the reversible solution-to-gel transition. Particularly, the re-gelation of DMSO induced by CO₂ bubbling could be directly observed without the aid of the heating-and-cooling operation. And the reversible sensing process could be repeated several times with the excellent chemical stability of the gelation system after the repeated stimuli of fluoride anion, CO₂ and N₂ with heating. These investigations indicate the developed organogelators own the applicable potential in the CO₂ detection.