Photochromic Properties of 3-Deoxyanthocyanidin Pigments in Nontoxic Solvents

The photochromic properties of some naturally occurring 3-deoxyanthocyanidin pigments were investigated in various nontoxic solvents. When luteolinidin, a representative 3-deoxyanthocyanidin, was dissolved in a mixture of weakly acidic water and an organic solvent with a relative permittivity between 20 and 34, it was possible to repeatedly induce coloration via ultraviolet irradiation and decoloration under light-shielded conditions. 1,3-Butanediol and ethanol, which are approved for use in foods, cosmetics, and household goods, were found to be appropriate organic solvents for this process. In addition, we confirmed that other 3-deoxyanthocyanidins, specifically apigeninidin and tricetinidin, which are commonly found in food grains and tea leaves, also exhibit photochromic properties.