Mixture comprising at least one of the two compounds of the structures Ia and Ib: where R 1, R 2, R 3, R 4, R 5, R 6, R 7, R 8 are each independently selected from: -H, -(C 1 -C 12)-alkyl, -O-(C 1 -C 12)-alkyl, -O- (C 6 -C 20) -aryl, -(C 6 -C 20)-aryl, halogen, COO-(C 1 -C 12)-alkyl, CONH-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-CON[(C 1 -C 12)-alkyl] 2, -CO-(C 1 -C 12)-alkyl, -CO-(C 6 -C 20)-aryl, -COOH, -OH, -SO 3 H, -SO 3 Na, -NO 2, -CN, -NH 2, -N[(C 1 -C 12)-alkyl] 2; X and Y are each independently selected from: -(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl, -(C 6 -C 20)-aryl-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-O-(C 1 -C 12)-alkyl, -(C 1 -C 12)-alkyl-(C 6 -C 20)-aryl, -(C 6 -C 20)-aryl-COO-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-CONH-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-CON[(C 1 -C 12)-alkyl] 2, -(C 4 -C 20)-heteroaryl, -(C 4 -C 20)-heteroaryl-(C 1 -C 12)-alkyl, -(C 5 -C 8)-Cycloalkyl-(C 4 -C 20)-aryl-CO-(C 6 -C 20)-aryl, Z is selected from: -(C 1 -C 12)-alkyl-, -(C 6 -C 20)-aryl-, -(C 6 -C 20)-aryl-(C 1 -C 12)-alkyl-, -(C 1 -C 12)-alkyl-(C 6 -C 20)-aryl-, - (C 4 -C 20)-heteroaryl-, -(C 6 -C 20)-aryl-CO-(C 6 -C 20)-aryl-, -(C 6 -C 20)-aryl- (C 6 -C 20)-aryl-; Q is selected from: -(C 1 -C 18)-alkyl-, -(C 1 -C 12)-alkyl-(C 1 -C 20)-aryl-, -(C 1 -C 18)-haloalkyl-, -NH-(C 1 -C 18)-alkyl, where the alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl and heteroaryl groups mentioned may be substituted, and a compound of the structure IIa: where R 20, R 30, R 40 are each independently selected from: -(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl, -(C 3 -C 12)-Cycloalkyl, two R 20 and R 30 or R 20 and R 40 or R 30 and R 40 radicals may also be bridged to one another, and may have a -(C 6 -C 20)-aryl-(C 6 -C 20)-aryl unit, where the alkyl, cycloalkyl and aryl groups mentioned may be substituted. R 1, R 2, R 3, R 4, R 5, R 6, R 7, R 8 are each independently selected from: -H, -(C 1 -C 12)-alkyl, -O-(C 1 -C 12)-alkyl, -O- (C 6 -C 20) -aryl, -(C 6 -C 20)-aryl, halogen, COO-(C 1 -C 12)-alkyl, CONH-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-CON[(C 1 -C 12)-alkyl] 2, -CO-(C 1 -C 12)-alkyl, -CO-(C 6 -C 20)-aryl, -COOH, -OH, -SO 3 H, -SO 3 Na, -NO 2, -CN, -NH 2, -N[(C 1 -C 12)-alkyl] 2; X and Y are each independently selected from: -(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl, -(C 6 -C 20)-aryl-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-O-(C 1 -C 12)-alkyl, -(C 1 -C 12)-alkyl-(C 6 -C 20)-aryl, -(C 6 -C 20)-aryl-COO-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-CONH-(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl-CON[(C 1 -C 12)-alkyl] 2, -(C 4 -C 20)-heteroaryl, -(C 4 -C 20)-heteroaryl-(C 1 -C 12)-alkyl, -(C 5 -C 8)-Cycloalkyl-(C 4 -C 20)-aryl-CO-(C 6 -C 20)-aryl, Z is selected from: -(C 1 -C 12)-alkyl-, -(C 6 -C 20)-aryl-, -(C 6 -C 20)-aryl-(C 1 -C 12)-alkyl-, -(C 1 -C 12)-alkyl-(C 6 -C 20)-aryl-, - (C 4 -C 20)-heteroaryl-, -(C 6 -C 20)-aryl-CO-(C 6 -C 20)-aryl-, -(C 6 -C 20)-aryl- (C 6 -C 20)-aryl-; Q is selected from: -(C 1 -C 18)-alkyl-, -(C 1 -C 12)-alkyl-(C 1 -C 20)-aryl-, -(C 1 -C 18)-haloalkyl-, -NH-(C 1 -C 18)-alkyl, where the alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl and heteroaryl groups mentioned may be substituted, and a compound of the structure IIa: where R 20, R 30, R 40 are each independently selected from: -(C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl, -(C 3 -C 12)-Cycloalkyl, two R 20 and R 30 or R 20 and R 40 or R 30 and R 40 radicals may also be bridged to one another, and may have a -(C 6 -C 20)-aryl-(C 6 -C 20)-aryl unit, where the alkyl, cycloalkyl and aryl groups mentioned may be substituted.