Base-induced multi-state fluorescence of a trefoil-shaped salicylaldehyde azine derivative

A trefoil-shaped salicylaldehyde azine derivative bearing multiple acidic protons displays base-induced multi-state luminescence. The azine was prepared through the reaction of 1,3,5-triformylphloroglucinol with 4-methoxysalicylaldehyde hydrazone. (1)H NMR spectroscopy revealed that the azine existed in solution at room temperature as an equilibrium mixture of two geometric isomers. The three-step deprotonation (four-state change) of the azine in solution was confirmed using (1)H NMR, UV-vis absorption, and emission spectroscopy.