Aryl ethers decorated gallic acid–naphthalimide conjugate: aggregation and sensing towards amines and F−
A gelator 1 containing naphthalimide and gallic acid derivatives has been designed and synthesised. It forms instant orange-coloured gels from different solvents such as CH3CN-1,4-dioxane (5:1, v/v), toluene-1,4-dioxane (5:1, v/v) and dimethylsulfoxide (DMSO). The morphology of the gels reveals the fibrous network. CH3CN-1,4-dioxane (5:1, v/v) gel exhibits higher mechanical strength than toluene-1,4-dioxane (5:1, v/v) gel as confirmed from lower tan δ value (tan δ = G″av/G′av) in rheological experiment. The CH3CN-1,4-dioxane (5:1, v/v) gel of 1 exhibits sharp response towards aliphatic amines over the aromatic amines causing rapid gel-to-gel transition with colour change. On the other hand, toluene-1,4-dioxane (5:1, v/v) gel of 1 selectively senses fluoride ion (F−) from a series of other basic anions by exhibiting colour change (from orange to blackish brown) of the gel state. By contrast, CH3CN-1,4-dioxane (5:1, v/v) gel underwent gel-to-sol transition in the presence of several anions and did not show any selectivity in sensing. Gelator 1 also shows measurable interaction towards aliphatic amines, F− and AcO− in CH3CN with distinguishable features in electronic spectra and colour change. Compound 1 and F−-coated paper strip which exhibits colour change on heating and cooling has been successfully used as writing kit.
