Patent ID: 7544448

Claim:
A method for marking a substrate which method comprises incorporating into or applying onto the substrate a composition comprising a tetrabenzodiazadiketoperylene pigment of formula I wherein X, Y, Z and G independently of each other are C 1-12 alkyl or branched alkyl, C 3-6 cycloalkyl, C 7-12 aralkyl, C 6-10 aryl, C 3-9 saturated or unsaturated heterocycle, halogen, —OR, CF 3 , —COOR,—CONR′R, NO 2 , NR′R, SO 3 H or SO 2 NR′R; R and R′, independently of each other are hydrogen, C 1-8 alkyl or branched alkyl, C 3-6 cycloalkyl, C 6-10 aromatic or C 7-12 aralkyl; and m, n, o and p are independently 0, 1, 2, 3 or 4, when m, n, o or p is 2, 3 or 4, each X, Y, Z or G substituent may each be a different group as defined above, and then exposing one or more parts of the substrate to laser radiation or heat to obtain a fluorescent form of the pigment of formula I to produce a fluorescent marking.