A novel pyrene-containing fluorescent organogel derived from a quinoline-based fluorescent porbe: Synthesis, sensing properties, and its aggregation behavior

A new family of pyrene-containing compounds 2-4 derived from aminoquinoline-containing fluorescent probe 1 were successfully synthesized and well characterized. The investigation of the absorption and emission spectra of these compounds revealed that the photophysical properties were significantly affected by the substitution of pyrene. Moreover, these compounds exhibited selective fluorescence behaviour towards Zn²⁺ in aqueous solution. The gelation properties of these compounds were investigated by the "stable to inversion of a test tube" method. Interestingly, 1,8-bis-substituted compound 4 displayed stable gel-formation properties in acetone, dioxane, tetrahydrofuran, ethyl acetate, chloroform, and dichloromethane. The morphologies of the xerogels were investigated by scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM). The concentration- and temperature-dependent emission properties, and concentration- and temperature-variable ¹H NMR spectroscopy of compound 4 were investigated, which suggested that both π-π stacking interaction and hydrogen bonding were the driving forces for the process of self-aggregation and the gel formation. In addition, studies on the luminescence properties indicated that 4 had the ability to form a fluorescent organogel with interesting fluorescence behaviour. More importantly, it was found that compound 4 could form a stimuli-responsive gel that had a sensitive gel-to-sol transition response to heating or adding Zn²⁺.