Schiff bases derivatives containing salicylaldimine and (benzo)pyrazole with fluorescence performance as dissociative proton detection probes in water/oil phases system.

In order to exploit novel fluorescence materials with probe properties, salicylaldehyde was introduced into pyrazole (A1), methylpyrazole (A2), indazole (A3), and methylindazole (A4) through an imine bond. The fluorescence quantum yield of these compounds in solid state (11.2 %-34.3 %) is significantly higher than that in liquid state (oil and water phases). Among them, A4 exhibits better fluorescence performance compared to the other title compounds. This phenomenon was caused by compound A4 possesses both a benzoheterocyclic heterocycle (indazole) and an electron-donating group (methyl). These two categories of electron-donating fragments make compound A4 as a kind of donor-π-donor (D-π-D) system. In addition, compound A4 can transform from enol to ketone under acidic conditions, and also significantly enhancing its fluorescence performance (fluorescence quantum yield increased from 4.1 % to 26.4 % in biodiesel). This process enables A4 to be used for acidity detection in biodiesel system.