Compound having the general structure I: where R 1, R 2, R 3, R 4, R 5, R 6, R 7, R 8 are 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, -S-alkyl, -S-aryl, halogen, COO-(C 1 -C 12)-alkyl, CONH-(C 1 -C 12)-alkyl, -CO-(C 1 -C 12)-alkyl, -CO-(C 6 -C 20)-aryl, -COOH, -OH, -SO 3 H, -CN, -NH 2, -N[(C 1 -C 12)-alkyl] 2; X is selected from: - (C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl, -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl, and the two radicals in at least one of the four following radical pairs are not the same radical: R 1 and R 8, R 2 and R 7, R 3 and R 6, R 4 and R 5; and the R 3 and R 4 radicals are not joined to one another via a carbon chain; where the alkyl and aryl groups mentioned may be substituted as follows: substituted -(C 1 -C 12)-alkyl groups and substituted -(C 1 -C 12)-alkoxy groups may have one or more substituents, depending on their chain length, the substituents are each independently selected from -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl, -(C 6 -C 20)-aryl, fluorine, chlorine, cyano, formyl, acyl or alkoxycarbonyl; substituted -(C 6 -C 20)-aryl groups and -(C 6 -C 20)-aryl-(C 6 -C 20)-aryl groups may have one or more substituents, depending on the ring size, and these substituents 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. R 1, R 2, R 3, R 4, R 5, R 6, R 7, R 8 are 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, -S-alkyl, -S-aryl, halogen, COO-(C 1 -C 12)-alkyl, CONH-(C 1 -C 12)-alkyl, -CO-(C 1 -C 12)-alkyl, -CO-(C 6 -C 20)-aryl, -COOH, -OH, -SO 3 H, -CN, -NH 2, -N[(C 1 -C 12)-alkyl] 2; - H, -(C 1 -C 12)-alkyl, -O-(C 1 -C 12)-alkyl, -O-(C 6 -C 20)-aryl, -(C 6 -C 20)-aryl, -S-alkyl, -S-aryl, halogen, COO-(C 1 -C 12)-alkyl, CONH-(C 1 -C 12)-alkyl, -CO-(C 1 -C 12)-alkyl, -CO-(C 6 -C 20)-aryl, -COOH, -OH, -SO 3 H, -CN, -NH 2, -N[(C 1 -C 12)-alkyl] 2; X is selected from: - (C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl, -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl, - (C 1 -C 12)-alkyl, -(C 6 -C 20)-aryl, -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl, and the two radicals in at least one of the four following radical pairs are not the same radical: R 1 and R 8, R 2 and R 7, R 3 and R 6, R 4 and R 5; and the R 3 and R 4 radicals are not joined to one another via a carbon chain; where the alkyl and aryl groups mentioned may be substituted as follows: substituted -(C 1 -C 12)-alkyl groups and substituted -(C 1 -C 12)-alkoxy groups may have one or more substituents, depending on their chain length, the substituents are each independently selected from -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl, -(C 6 -C 20)-aryl, fluorine, chlorine, cyano, formyl, acyl or alkoxycarbonyl; substituted -(C 6 -C 20)-aryl groups and -(C 6 -C 20)-aryl-(C 6 -C 20)-aryl groups may have one or more substituents, depending on the ring size, and these substituents 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. substituted -(C 1 -C 12)-alkyl groups and substituted -(C 1 -C 12)-alkoxy groups may have one or more substituents, depending on their chain length, the substituents are each independently selected from -(C 3 -C 12)-cycloalkyl, -(C 3 -C 12)-heterocycloalkyl, -(C 6 -C 20)-aryl, fluorine, chlorine, cyano, formyl, acyl or alkoxycarbonyl; substituted -(C 6 -C 20)-aryl groups and -(C 6 -C 20)-aryl-(C 6 -C 20)-aryl groups may have one or more substituents, depending on the ring size, and these substituents 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.