Patent ID: 7678515

Claim:
An image forming medium, comprising: a substrate; and an imaging layer coated on or impregnated into the substrate, wherein the imaging layer comprises an imaging composition that exhibits a reversible transition between a colorless state and a colored state and further comprises a thermally gated diarylethene photochromic material dissolved in a solvent or polymeric binder, and further wherein the diarylethene photochromic material comprises a diarylethene molecule represented by a general formula selected from the group consisting of wherein in formula (I) each X independently represents a hydrogen, an alkyl chain having 1 to 20 carbon atoms, cyano, fluorine, bromine, chlorine or an iodine atom; in formula (II) X represents S or O; in formula (IV) X represents S, O or C═O, and Y represents O, CH 2 or C═O; in formula (V) Y represents CH 2 or C═O; in formula (VI), X represents CH or N; in formula (VII), Y represents CH 2 or C═O; in formula (VIII), X represents S or O; and in formulas (II), (III), (V) and (VIII), R 1 -R 3 represents an alkyl group wherein the alkyl group can be a straight, branched or cyclic, substituted or unsubstituted, from 1 to about 40 carbon atoms, an substituted or unsubstituted aromatic or heteroaromatic group; further wherein: A represents a formula selected from the group consisting of (g), (h) and (i) as shown below; and B represents a formula selected from the group consisting of (j), (k) and (l) as shown below and further wherein: R 4 and R 8 independently represent hydrogen bond forming groups selected from the group consisting of a carboxy, hydroxy, amino, amino acid, amide, and peptide group which form pairwise hydrogen bonds with each other; R 5 and R 9 independently represent a hydrogen atom, a halogen atom, an aryl group, a substituted or unsubstituted alkylaryl group wherein hetero atoms either may or may not be present in the alkyl portion of the alkylaryl group or the aryl portion of the alkylaryl group, a saturated or unsaturated hydrocarbons which is optionally substituted, a fluoroalkyl group, a cyano group, a formyl group, or a carboxy group; R 6 and R 10 independently represent a hydrogen atom, an alkyl group, a halogen atom, an alkoxy group, a fluoroalkyl group, a cyano group, an aryl group, or a substituted alkylaryl group; R 7 and R 11 independently represent an alkyl group, an aryl group, or an alkylaryl group including substituted alkylaryl groups, unsubstituted alkylaryl groups, and wherein hetero atoms either may or may not be present in the alkyl portion of the alkylaryl group or the aryl portion of the alkylaryl; Q represents direct bonds, aryl, alkylaryl, heteroaryl, heteroalkylaryl, straight, branched or cyclic, hetero substituted or unsubstituted, alkyl groups from 1 to about 10 carbon atoms, alkenyl, alkynyl, or fluoroalkyl groups, wherein hetero atoms either may or may not be present and are optionally substituted; and U and Z each independently represent sulfur or oxygen atoms.