Use of aryl-or alkyloxy-substituted phthalocyanines as marking substances for liquids

A method for marking a liquid, comprising the step of adding to the liquid as a marker a phthalocyanine of the formula (I)

• where the symbols and indices in the formula (I) have the following definitions:
• M is twice hydrogen, twice lithium, magnesium, zinc, copper, nickel, VO, TiO, AlCl, AlOCOCH3, AlOCOCF3, SiCl2 or Si(OH)2;
• m is 1, 2, 3 or 4;
• n is the same or different and is 0, 1, 2, 3 or 4;
• r is the same or different and is 0, 1, 2, 3 or 4;
• m+r is 1, 2, 3 or 4;
• n+r is 0, 1, 2, 3 or 4;
• R is the same or different and is
• R1 is the same or different and is H, halogen or R2;
• R2 is the same or different and is (C1-C18)-alkyl, (C4-C8)-cycloalkyl, (C2-C12)-alkenyl, (C8-C10)-aryl, (C7-C20)-aralkyl or (C2-C12)-alkynyl, where aryl radicals are unsubstituted or substituted by one or more halogen, cyano, nitro, hydroxyl, amino, C1-C20-alkyl which is optionally interrupted by from 1 to 4 oxygen atoms in ether function, C1-C20-alkoxy, C1-C20-alkylamino or C1-C20-dialkylamino;
• R3 is the same or different and is R1, or two R3 radicals or one R1 radical and one R3 radical together form a further ring system;
• R4, R5, R6 are the same or different and are each H, halogen, CH3 or C2H5;
• Y1, Y2, Y3, Y4, Y5, Y6 are the same or different and are each (C1-C4)-alkylene which is unsubstituted or substituted by one or more halogen atoms;
• s is 0, 1, 2, 3, 4, 5, or 6;
• and
• t is 0, 1, 2, 3.