The invention relates to an ink composition comprising a dye, wherein said dye comprises a structure of Formula I: wherein R1 represents a
hydrogen atom, a cyano group, a substituted or unsubstituted
alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aralkyl group, an alkylthio group, an arylthio group an
acyl group, a substituted
acyl group, a carboxyl group, a carbamoyl group, or a heterocyclic group; Za represents one of —N═, —NH— or —C(R8)═; and Zb and Zc each independently represents one of —N═or —C(R8)═; R8 represents a
hydrogen, a substituted or unsubstituted
alkyl or a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group or a heterocyclic group; [0001]R2 represents a
hydrogen, a substituted or unsubstituted
alkyl group, a substituted or unsubstituted
aryl group, a
halogen, a cyano group, a carboxyl or substituted carboxyl group, an
acyl group, a substituted acyl group, a carbamoyl group, a nitro group, an alkyl or
aryl sulfone, a
sulfonic acid, a substituted or unsubstituted primary or secondary alkyl sulfonamide, a substituted or unsubstituted
aryl sulfonamide or a heteroaryl group; [0002]R3 may be hydrogen or any non-metallic group; [0003]R4, R5, R6 may be H or any non-metallic group with the proviso that at least one of R4 or R6 represents any ionizable group which is capable of imparting water
solubility to the dye; [0004]R5 may be present in any other position on the aromatic ring that is not occupied by R4 or R6.