Stabilization of chemically flexible indigo dye against photodegradation under solvent condition through intercalation into layered double hydroxide

An indigo derivative with a flexible structure and water solubility was synthesized and further stabilized in a layered double hydroxide. Although the synthesized indigo derivative takes advantage of high water-solubility thanks to hydrophilic carboxymethyl groups, its stability in water was significantly low showing 91 % decomposition even in a dark environment. Under light irradiation, the indigo derivative became more fragile, being subjected to both photoisomerization and photodecomposition simultaneously. In order for stabilization under water conditions, the indigo derivative was hybridized with a layered double hydroxide by intercalation. The hybrid exhibited significant stability in a water suspension for more than 2 days under darkness and for 5 h even with 660 nm light irradiation. The stability was thought to be due to the isolation of the indigo derivative from the solvents and suppression of its trans-cis isomerization by the confinement effect in the interlayer space of the layered double hydroxide.