Fluorine-free diarylethene photochromic compound system for reversible hair coloration

A product for coloring a substrate, the product comprising:

• a container;
• a coloring composition in the container, the coloring composition comprising a photochromic compound comprising at least one of:
• (A) a fluorine-free first compound comprising (1) a cyclic bridge comprising one ethylenically unsaturated bond, (2) a first substituent comprising a first unsaturated heterocycle bonded to a first carbon atom in the ethylenically unsaturated bond and a first aromatic group or a first halogen bonded to the first unsaturated heterocycle, and (3) a second substituent comprising a second unsaturated heterocycle bonded to a second carbon atom in the ethylenically unsaturated bond and a second aromatic group bonded to the second unsaturated heterocycle;
• (B) a fluorine-free second compound comprising an activated analog of the fluorine-free first compound;
• and
• (C) a fluorine-free third compound comprising a dyotropic rearrangement of the fluorine-free first compound;
• a light source adapted to provide one or both of activating electromagnetic radiation (EMR) having a wavelength of 250 nm to 395 nm and deactivating EMR having a wavelength of 400 nm to 1400 nm.