Polychromic substances and their use

A diacetylene compound of formula (I):

• wherein one of X and Y is a divalent straight-chain or branched alkylene group of up to 24 C atoms, a divalent phenylene group, or a combination of both alkylene and phenylene, and the other of X and Y is a bond or a divalent straight-chain or branched alkylene group of up to 24 C atoms, a divalent phenylene group, or a combination of both alkylene and phenylene;
• wherein X and/or Y are substituted with a hydroxyl group in the α position with respect to the diacetylene group;
• wherein V is a divalent bridging group selected from —S—, —O—, —NHR′—, amide, ester, thioester, carbonyl, and a carbamate group;
• wherein R′ is hydrogen or alkyl;
• wherein Q is a bond or a divalent bridging group selected from —S—, —O—, —NHR′—, amide, ester, thioester, carbonyl, and a carbamate group;
• wherein R′ is hydrogen or alkyl;
• wherein R1 is H or alkyl;
• and
• wherein R2 is alkyl.