A new cholesterol-naphthalimide conjugate: aggregation and sensing of CN− and CO2 under different conditions

Abstract

Cholesterol-coupled naphthalimide derivative 1 has been designed, synthesized, and successfully established as a supramolecular gelator. It shows gelation in DMF and DMF:MeOH (1 : 1, v/v) involving weak forces. The aggregation behavior is explained spectroscopically as well as theoretically. The gels are stable and exhibit good viscoelastic properties. The storage modulus (G′) in each gel is considerably higher than the loss modulus (G′′). The lower value of tan δ for DMF–MeOH (1 : 1, v/v) gel compared to the DMF gel demonstrates the better gelation behaviour of 1 in DMF–MeOH (1 : 1, v/v). As an application, the anion recognition and CO₂ detection using the gelator 1 have been discussed under different conditions. The DMF–MeOH (1 : 1, v/v) gel of 1 recognizes CN⁻-over a series of other anions by showing the gel-to-gel colour change. In DMF solvent, 1 shows measurable interaction to CN⁻ and F⁻ with a detection limit of ∼10⁻⁸ M, and they are distinguished by Ca(ClO₄)₂. The F⁻/CN⁻- activated 1, either in solution or in the gel state, successfully detects CO₂ by the naked eye. The detection has been possible also by the test-kit method.