Described is the use of benzotropolone and their derivatives, especially the compounds of formula (1) wherein R2, R3, R4, R5 and R6 independently of one another are hydrogen OH C1-C30alkyl, C2-C30al-kenyl, C1-C30alkoxy, C3-C12cycloalkyl or C1C30hydroxyalkyl, which may be substituted by one or more E and/or interrupted by one or more D C6-C20aryl, which may be substituted by one or more G C4-C20heteroaryl, which may be substituted by one or more G, C2-C18alkenyl, C2-C18alkynyl, C7-C25aralkyl, CN, or &mdashCO&mdashR17 C1-C30mono- or dialkylamino COR9 COOR9 CONR9R10 CN SO2R9 OCOOR9 OCOR9 NHCOOR9 NR9COR10 NH2 *&mdash(CO)&mdashNH&mdash(CH2)n1&mdash(PO)&mdash(OR11)2 &mdash(CO)&mdashO&mdash(CH2)n1&mdash(PO)&mdash(OR11)2 sulphate sulphonate phosphate phosphonate &mdash(CH2)n2&mdash[O&mdash(SO2)]n3&mdashOR11 &mdashO&mdash(CH2)n4(CO)n5&mdashR11 &mdash(O)n6&mdash(CH2)n7&mdash(PO)&mdash(OR9)2 &mdash(O)n6&mdash(CH2)n7&mdashSO2&mdashOR9 halogen organosilanyl organo-siloxanyl or a sugar residue linked directly in an &alpha- or &bgr-mode via the anomeric oxygen to the benzotropolone system or via a linear or branched alkylene, alkenylene, alkadiene or alkatriene spacer (sugar-(CH2)n&mdash(X1)1 or 0-benzotropolone system, wherein n=1-10 and X1=&mdashO&mdash &mdash(CO)&mdash &mdashO&mdashCO&mdash &mdashCOO&mdash, &mdashNH&mdash &mdashS&mdash &mdashSO2&mdash) R1, R7 and R8 independently of one another are hydrogen C1C12alkyl or C3-C12-cycloalkyl, which may be substituted by one or more E and/or interrupted by one or more D C6-C20aryl, which may be substituted by one or more G C4-C20heteroaryl, which may be substituted by one or more G, C2-C18alkenyl, C2-C18alkynyl, C7-C25aralkyl, or COOR9 COR9 CONR9R10 SO3R9 SO2R9 PO3(R9)2 PO2(R9)2 organosilanyl organosiloxanyl or a sugar residue linked directly in an &alpha- or &bgr-mode via the anomeric oxygen to the benzotropolone system or via a linear or branched alkylene, alkenylene, alkadiene or alkatriene spacer (sugar-(CH2)n&mdash(X2)1 or 0&m
