Disclosed is the use of the compounds of formula (1) wherein R1 and R2 independently of one another are hydrogen unsubstituted or substituted C1- C12 alkyl unsubstituted or substituted C3 -C12 cycloalkyl unsubstituted or substituted C6- C20 aryl or unsubstituted or substituted C2-C20 alkenyl R3 is PO3 R1 R2 COOR6 COR7 CONR7 R8 -SO2 R6 CN unsubstituted or substituted C6- C20 aryl R4 is unsubstituted C6- C20 aryl or C6- C20 aryl which is substituted by at least one C1- C18 alkyl, C1- C18 alkoxy, C3- C12 cycloalkyl, hydroxy, amino, mono-or di-C1- C18 alkylamino, -NR10 COR11 or the radical of formula (1a) or unsubstituted or substituted C4 -C20 heteroaryl R5 is hydrogen substituted or unsubstituted C1 -C20 alkyl unsubstituted or substituted C3 - C12 cycloalkyl unsubstituted or substituted C6 -C20 aryl or unsubstituted or substituted C4- C20 heteroaryl or R4 and R5 form a cycloaliphatic ring R6, R7 and R8 independently from each other are hydrogen C1- C18 alkylor C3-C12 cycloalkyl, which may be substituted by one or more E and/or interrupted by one or more D or C6- C20 aryl, which may be substituted by G or R7 and R8 together form a five or six membered ring D is -CO- -COO- -S- -SO- -SO2 - -O- -NR9 - -SiR12 R13 - -POR14 - -CR15 =CR16 - or -C≡C- E is -OR17 -SR17 -NR10 R11 -NR10 COR11 -COR11 -COOR 11 -CONR10 R11 -CN halogen SO3 R18 SO2 R18 PO3 (R18 )2 or PO2 (R18 )2 G is E C1-C18 alkyl, which is optionally interrupted by D C1-C18 perfluoroalkyl C1 -C18 alkoxy, which is optionally substituted by E and/or interrupted by D wherein R9, R10 and R11, independently of each other are hydrogen C6 -C18 aryl which is optionally substituted by C1-C18 alkyl or C1-C18 alkoxy C1-C18 alkyl, which is optionally interrupted by -O-or R10 and R11 together form a five or six membered ring R12 and R13 independently of each other are hydrogen C1- C18 alkyl or C6-C18 aryl which is optionally substituted by C1-C18 alkyl R14 is C1-C18 alkyl or C6-C18 aryl, which is optionally substituted by C1-C18
