The isomerization and metal chelation of spironaphthoxazine (SNO) in ethanol solutions have been investigated by measuring the UV-vis absorption spectra as a function of time.The protonated species of merocyanine (MC), an isomer of SNO, was gradually formed in the solutions containing SNO and aluminum ions in the dark. The proton was provided by the reaction of the aluminum ions with a slight amount of water contained in the ethanol solvent.The protonated species was slowly transformed into the aluminum chelate complex of MC by ligand exchange of the ethanol-solvated aluminum for MC in the dark. UV irradiation promoted the isomerization and chelation without forming the protonated species. The spectroscopic analysis with various compositional ratios of SNO and aluminum ions revealed that one aluminum ion was coordinated to three bidentate MC ligands in the ethanol solution.

The reaction of spironaphthoxazine (SNO) with acid in ethanol was investigated by spectroscopic analyses SNO was protonated and then transformed into a complex in an acidic ethanol solution in the dark. It is presumed that the complex contains a hydrated proton and its structure is similar to that of the metal complex of a merocyanine-type isomer photoderived from SNO based on its UV-vis absorption and fluorescence spectra.The complex dissociated into SNO by adding base. The complex was further changed under acidic conditions after a long time.Highly concentrated acid decomposed SNO to an indoline compound having a carboxyl group and 1-amino-2-naphthol, which was revealed by fluorescence, IR, and GC-MS analyses. These reaction processes were promoted by UV irradiation.