The present invention relates to photoinitiator compounds of the formula (1) wherein X is O, S or a direct bond; Y is O, S or CR9R10; R1, R2, R3, R4, R5, R6, R7 and R8 independently of each other are hydrogen, halogen, C1-C18alkyl, C5-C10cycloalkyl, C2-C18alkenyl, phenyl, C1-C4alkoxy, C5-C7cycloalkoxy, phenoxy, C1-C4-alkylthio, C5-C7cycloalkylthio, phenylthio, di(C1-C4alkyl)amino, di(C5-C7cycloalkyl)amino, N-morpholinyl, N-piperidinyl or a group of formula (2) provided that one or more than one of R1, R2, R3, R4, R5, R6, R7 or R8 is a group of formula (2); R9, R10 independently of each other are hydrogen, C1-C18alkyl, C2-C12alkenyl, C5-C10cycloalkyl, phenyl-C1-C4alkyl, phenyl or together with the C atom to which they are attached form a 5-membered, 6-membered or 7-membered ring; and R11 is hydrogen, C1-C18alkyl, C5-C10cycloalkyl, C2-C12alkenyl, phenyl-C1-C4alkyl or phenyl.