Red thermochromic dyes and their ink compositions

A red thermochromic dye having the formula (I):

• Wherein the dashed line (represented by ------) represents an optional bond;
• X is at least one of nitrogen substituted by hydrogen or alkyl/aryl groups, oxygen, or sulfur;
• Y is at least one of methine (CH) or nitrogen;
• R1 and R2 are the same or different and are independently selected as at least one of hydrogen, substituted or non-substituted alkyl or aryl groups, the two alkyl groups together with the nitrogen atom to which they are attached form a morpholinyl ring;
• the NR1R2 group can be attached to the phenyl moiety as well as the naphthyl moiety;
• the R3 groups on either phenyl or naphthyl moieties are independently at least one of H, halogen, nitro, amine or substituted amine, alkyl or substituted alkyl, as well as phenyl or substituted phenyl groups;
• R4 is at least one of amino, mono- or bis-substituted alkyl or phenyl amino group, and phenyl group with a para-position substituted by dialkylamino group.