Colorimetric anion sensing and color imaging based on catalyzed deprotection in a new azonaphthol chromophore

We synthesized an ortho-phenylazonaphthol compound of which hydroxyl group was protected by a thermo-labile tert-butoxycarbonyl (t-Boc) group, in which hydroxyazo- and hydrazone-tautomerism could be blocked. The chromophore obtained by protection with t-Boc group was exclusively present as a hydroxyazo tautomer and exhibited blue-shifted absorption spectrum compared to their parent azohydrazone tautomerizing chromophore. With this compound, we performed colorimetric anion sensing based on the deprotection-induced possible azohydrazone formation in dye chromophore subsequently resulting in naked-eye color change. Besides, the t-Boc protected chromophore could be used as a color imaging material via thermolysis of thermo-labile t-Boc groups resulting in formation of azohydrazone form with red shifted absorption.