Thermochromic materials

In a reversible thermochromic material comprising (a) one or more electron-donating, chromatic organic compounds selected from the group consisting of diaryl phthalides, aryl phthalides, indolylphthalides, polyarylcarbinols, leucoauramines, acrylauramines, arylauramines, rhodamine B lactams, indolines, spiropyrans, fluorans, thiofluorans, phenothiazines, triphenylmethanes, diarylarylfurans, spiroxanthenearylfurans, and chromenoindoles, (b) one or more compounds, compounds, which are capable of reversibly accepting electrons of said organic compound, selected from the group consisting of phenolic hydroxy group-containing compounds and derivatives thereof and carboxyl group-containing compounds and derivatives thereof, and (c) one or more compounds, which are controlling the temperature and sensitivity of coloration/decoloration of said thermochromic material, selected from the group consisting of alcohols, esters, ketones, esters, acid amides and carboxylic acids, the ratio of each component to others (a):(b):(c) being 1:0.1 to 10:1 to 100 by weight,

• the improvement which comprises said thermochromic material further containing (d) one or more radical cationic compound selected from the group consisting of N-radical cationic, P-radical cationic, O-radical cationic and S-radical cationic compounds having aromatic ring(s), in an amount of from 0.01 to 5 parts by weight per 1 part by weight of said electron-donating chromatic organic compound, said radical cationic compound interacting with said electron-donating, chromatic organic compound to stabilize said compound, resulting in a thermochromic mateiral with an improved resistance to light.