| abstract |
A reversible thermochromic system comprising a) a compound of the formula (I) or a tautomer thereof (I) wherein R1 is C1-C18alkyl, C2-C18alkenyl, C3-C12cycloalkyl, C3-C12cycloalkyl substituted by 1, 2 or 3 C1-C4alkyl; or C7-C12phenylalkyl; R2 and R3 are hydrogen or R2 and R3 together form a group -CH=CH-CH=CH-; and R4 is hydrogen, -NO2, -SO2-R1 or (4-nitrophenyl)azo; and b) a compound containing a group of the formula (II). |