Optimized time temperature indicator

A time temperature indicator comprising a spiropyran and a modifier which is able to form with the spiropyran mixed solids with an amorphous, crystalline or mixed amorphous-crystalline structure, whereby the modifier is

• selected from the group of esters consisting of CH3—(CH2)n—COOC1-C18alkyl with n=10-18;
• cholesterol oleate;
• citric acid ester;
• p-hydroxybenzoate;
• bornylacetate, dicarboxylic acid C1-C18alkyl-O—OC—(CH2)m—COOC1-C18alkyl with m=2-20;
• and esters from sugar alcohols;
• or the modifier is
• a C6-C20 alkylalcohol;
• a cyclic alcohol;
• a polyalcohol;
• a polyether;
• a fatty acid;
• a salt of a carboxylic acid;
• a diterpene acid;
• urea or imidazole;
• a cyclic ketone;
• 2,6-di-t-butyl-4-methoxyphenol or a 4-hydroxy-3-methoxybenzaldehyd;
• a chroman-6-ole;
• 4-isopropenyl-1-methylcyclohexen (R-limonene);
• naphthalene, phenanthrene;
• sodium dodecylsulfate;
• a Zn complex of hydroxy naphthoic acid;
• an adduct of a second indolenin unit to the spiropyran;
• or
• a mixed solid of two different spiropyrans.