A 1,8-naphthalimide–pyridoxal conjugate as a supramolecular gelator for colorimetric read out of F− ions in solution, gel and solid states†
Abstract
A naphthalimide–pyridoxal conjugate 1 has been designed and synthesized. Compound 1 forms a stable greenish yellow colored gel in DMSO : H2O (8 : 1 v/v). Rheological study reveals that the gel is mechanically strong (G′> G′′) over a wide range of applied strains. The morphology of the gel as determined by FESEM shows a highly cross-linked fibrous network. The gel is anion-responsive and is selectively transformed into a sol with a color change from greenish yellow to deep blue only in the presence of F− among other anions. In CH3CN, compound 1 was also sensitive to basic anions such as F− and AcO− ions. In solution, F− was differentiated from AcO− through a color change. While the yellow colored solution of 1 in acetonitrile was changed into deep blue in the presence of F−, AcO− ions gave a faint blue coloration. A similar colorimetric differentiation of F− from AcO− has been possible in CH3CN by a reusable Schiff base-linked Merrifield resin 1a or 1b.