Dithiolene Metal Complex Colorless IR Absorbers

A method of using colorless IR absorbers comprising

• a) treating a material with a compound of formula I and/or II
• wherein
• M is Ni, Pd, Pt,
• X1 is oxygen,
• X2 and X3 are each independently of the other sulfur or oxygen,
• R1, R2, R3, R4, R5 and R6 are each independently of the others hydrogen, NR7R8, unsubstituted or substituted C1-C18alkyl, C1-C18 alkyl wherein the alkylene chain is interrupted with oxygen, unsubstituted or substituted C1-C18alkenyl, unsubstituted or substituted aryl, unsubstituted or substituted arylalkyl or unsubstituted or substituted heteroarylalkyl, R7 and R8, each independently of the other, being unsubstituted or substituted C1-C18alkyl, unsubstituted or substituted aryl, unsubstituted or substituted arylalkyl or unsubstituted or substituted heteroarylalkyl,
• wherein the material is a security print, an invisible and IR readable bar code, a laser-welded plastic, a dried print, a fixed toner on paper, a laser marked plastic, or a heated preform,
• optionally a further IR absorber;
• and
• b) using the treated material of a) for security printing, invisible and IR readable bar codes, laser-welding of plastics, drying of print, fixing of toners on paper, laser marking, and heating of plastics preforms.