Thermal imaging method

Abstract From the Canadian patent

Abstract of the Disclosure A thermal imaging method is provided which employs as color-forming co-reactants, (a) a substantially colorless di- or triarylmethane compound possessing on the meso carbon atom within its triarylmethane structure an aryl group substituted in the ortho position with a nucleophilic moiety which is ring-closed on the meso carbon atom and (b) an electrophilic reagent which upon heating and contacting said di- or triarylmethane compound undergoes a bimolecular nucleophilic substitution reaction with the nucleophilic moiety to form a colored, ring-opened di- or triarylmethane compound.