A compound of the formula wherein n is 0 or 1; R 1 is selected from the group consisting of hydrogen, C 1 -C 24 -alkyl, C 1 -C 24 -haloalkyl, C 3 -C 24 -cycloalkyl, C 6 -C 10 -aryl and C 6 -C 10 -aryl-C 1 -C 10 -alkylene, where the rings of cycloalkyl, aryl, and aryl-alkylene in the three last-mentioned radicals are unsubstituted or substituted with one or more substituents R 7, and where C 1 -C 24 -alkyl, C 1 -C 24 -haloalkyl and the alkylene moiety of C 6 -C 10 -aryl-C 1 -C 10 -alkylene may be interrupted by one or more heteroatoms or heteroatomic groups selected from O, S and NR 8; R 3, R 4, R 5 and R 6, independently of each other, are selected from C 6 -C 10 -aryloxy, C 2 -C 10 -heteroaryl or C 6 -C 10 -aryl, wherein C 6 -C 10 -aryloxy is substituted by one or more identical or different substituents R 7; C 2 -C 10 -heteroaryl is unsubstituted or substituted by one or more identical or different substituents R 7 and C 6 -C 10 -aryl is substituted by one or more identical or different substituents R 7; R 2 and R 2' together form a group of formula represents the bond to the rylene basic skeleton, the group of formula is unsubstituted or substituted with one or more substituents R 7, or the group of formula may be part of an annulated ring system, which is unsubstituted or substituted with one or more substituents R 7, or in case of the group of formula two substituents R 7 may form a group wherein represents the bond to the group of formula, R 1' is selected from the group consisting of hydrogen, C 1 -C 24 -alkyl, C 1 -C 24 -haloalkyl, C 3 -C 24 -cycloalkyl, C 6 -C 10 -aryl and C 6 -C 10 -aryl-C 1 -C 10 -alkylene, where the rings of cycloalkyl, aryl, and aryl-alkylene in the three last-mentioned radicals are unsubstituted or substituted with one or more substituents R 7, and where C 1 -C 24 -alkyl, C 1 -C 24 -haloalkyl and the alkylene moiety of C 6 -C 10 -aryl-C 1 -C 10 -alkylene may be interrupted by one or more heteroatoms or heteroatomic groups selected from O, S and NR 8; each R 7 is selected from C 1 -C 24 -alkyl, C 1 -C 24 -fluoroalkyl, C 1 -C 24 -alkoxy, fluorine, chlorine or bromine; R 8 is hydrogen, C 1 -C 20 -alkyl, C 3 -C 24 -cycloalkyl, heterocycloalkyl, hetaryl or C 6 -C 10 -aryl. n is 0 or 1; R 1 is selected from the group consisting of hydrogen, C 1 -C 24 -alkyl, C 1 -C 24 -haloalkyl, C 3 -C 24 -cycloalkyl, C 6 -C 10 -aryl and C 6 -C 10 -aryl-C 1 -C 10 -alkylene, where the rings of cycloalkyl, aryl, and aryl-alkylene in the three last-mentioned radicals are unsubstituted or substituted with one or more substituents R 7, and where C 1 -C 24 -alkyl, C 1 -C 24 -haloalkyl and the alkylene moiety of C 6 -C 10 -aryl-C 1 -C 10 -alkylene may be interrupted by one or more heteroatoms or heteroatomic groups selected from O, S and NR 8; R 3, R 4, R 5 and R 6, independently of each other, are selected from C 6 -C 10 -aryloxy, C 2 -C 10 -heteroaryl or C 6 -C 10 -aryl, wherein C 6 -C 10 -aryloxy is substituted by one or more identical or different substituents R 7; C 2 -C 10 -heteroaryl is unsubstituted or substituted by one or more identical or different substituents R 7 and C 6 -C 10 -aryl is substituted by one or more identical or different substituents R 7; R 2 and R 2' together form a group of formula represents the bond to the rylene basic skeleton, the group of formula is unsubstituted or substituted with one or more substituents R 7, or the group of formula may be part of an annulated ring system, which is unsubstituted or substituted with one or more substituents R 7, or in case of the group of formula two substituents R 7 may form a group wherein represents the bond to the group of formula, R 1' is selected from the group consisting of hydrogen, C 1 -C 24 -alkyl, C 1 -C 24 -haloalkyl, C 3 -C 24 -cycloalkyl, C 6 -C 10 -aryl and C 6 -C 10 -aryl-C 1 -C 10 -alkylene, where the rings of cycloalkyl, aryl, and aryl-alkylene in the three last-mentioned radicals are unsubstituted or substituted with one or more substituents R 7, and where C 1 -C 24 -alkyl, C 1 -C 24 -haloalkyl and the alkylene moiety of C 6 -C 10 -aryl-C 1 -C 10 -alkylene may be interrupted by one or more heteroatoms or heteroatomic groups selected from O, S and NR 8; each R 7 is selected from C 1 -C 24 -alkyl, C 1 -C 24 -fluoroalkyl, C 1 -C 24 -alkoxy, fluorine, chlorine or bromine; R 8 is hydrogen, C 1 -C 20 -alkyl, C 3 -C 24 -cycloalkyl, heterocycloalkyl, hetaryl or C 6 -C 10 -aryl.