A compound of formula in which Z 1 and Z 2 signify independently from each other OR 9 or OR 10, wherein R 9 and R 10 signify independently from each other linear C 1 to C 3 alkyl or branched C 3 alkyl; or Z 1 and Z 2 signify independently from each other NR 2 R 3 or NR 4 R 5, wherein R 2 and R 4 signify independently from each other hydrogen, linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl, linear C 2, C 3 hydroxyalkyl or branched C 3 hydroxyalkyl, CH 2 CO 2 M, CH 2 CH 2 CONH 2 or CH 2 CH 2 CN, R 3 and R 5 signify independently from each other linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl, linear C 2, C 3 hydroxyalkyl or branched C 3 hydroxyalkyl, CH 2 CH 2 SO 3 M CH 2 CO 2 M, CH(CO 2 M)CH 2 CO 2 M or CH(CO 2 M)CH 2 CH 2 CO 2 M, benzyl, or R 2 and R 3 and/ or R 4 and R 5 signify together with their neighboring nitrogen atom a morpholine ring, and R 1 and R 6 signify independently from each other hydrogen, other linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl, linear C 2 to C 3 hydroxyalkyl or branched C 3 hydroxyalkyl, CH 2 CH 2 CONH 2 or CH 2 CH 2 CN, R 7 and R 8 signify independently from each other hydrogen, linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl, under the proviso that at least one of R 7 or R 8 is linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl; X and Y signify independently from each other CO 2 M or SO 3 M, m and n are 0, 1 or 2, under the proviso that at least one of m or n is at least 1, and M signifies a cation for balancing the anionic charge selected from the group comprising or essentially consisting of hydrogen, an alkali metal cation, alkaline earth metal cation, ammonium, ammonium which is mono-, di-, tri- or tetrasubstituted by a linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl radical, ammonium which is mono-, di-, tri- or tetrasubstituted by a or linear C 1 to C 4 hydroxyalkyl or branched C 3, C 4 hydroxyalkyl radical, ammonium which is di-, tri-, or tetrasubstituted by a mixture of linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl radical or linear C 1 to C 4 hydroxyalkyl or branched C 3, C 4 hydroxyalkyl radical or mixtures of said cations, wherein if R 7 is linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl, then n is at least 1, and/ or if R 8 is linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl, then m is at least 1. Z 1 and Z 2 signify independently from each other OR 9 or OR 10, wherein R 9 and R 10 signify independently from each other linear C 1 to C 3 alkyl or branched C 3 alkyl; or Z 1 and Z 2 signify independently from each other NR 2 R 3 or NR 4 R 5, wherein R 2 and R 4 signify independently from each other hydrogen, linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl, linear C 2, C 3 hydroxyalkyl or branched C 3 hydroxyalkyl, CH 2 CO 2 M, CH 2 CH 2 CONH 2 or CH 2 CH 2 CN, R 3 and R 5 signify independently from each other linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl, linear C 2, C 3 hydroxyalkyl or branched C 3 hydroxyalkyl, CH 2 CH 2 SO 3 M CH 2 CO 2 M, CH(CO 2 M)CH 2 CO 2 M or CH(CO 2 M)CH 2 CH 2 CO 2 M, benzyl, or R 2 and R 3 and/ or R 4 and R 5 signify together with their neighboring nitrogen atom a morpholine ring, and R 1 and R 6 signify independently from each other hydrogen, other linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl, linear C 2 to C 3 hydroxyalkyl or branched C 3 hydroxyalkyl, CH 2 CH 2 CONH 2 or CH 2 CH 2 CN, R 7 and R 8 signify independently from each other hydrogen, linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl, under the proviso that at least one of R 7 or R 8 is linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl; X and Y signify independently from each other CO 2 M or SO 3 M, m and n are 0, 1 or 2, under the proviso that at least one of m or n is at least 1, and M signifies a cation for balancing the anionic charge selected from the group comprising or essentially consisting of hydrogen, an alkali metal cation, alkaline earth metal cation, ammonium, ammonium which is mono-, di-, tri- or tetrasubstituted by a linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl radical, ammonium which is mono-, di-, tri- or tetrasubstituted by a or linear C 1 to C 4 hydroxyalkyl or branched C 3, C 4 hydroxyalkyl radical, ammonium which is di-, tri-, or tetrasubstituted by a mixture of linear C 1 to C 4 alkyl or branched C 3, C 4 alkyl radical or linear C 1 to C 4 hydroxyalkyl or branched C 3, C 4 hydroxyalkyl radical or mixtures of said cations,