Compounds of the formula (I), wherein m is 1 or 2; R 1 , R 2 , R 4 and R 5 independently of one another are hydrogen, C 1 -C 4 alkyl, C 5 -C 7 cyclo-alkyl, phenyl, C 1 -C 4 alkoxy, C 5 -C 7 cycloalkoxy or phenoxy; R 3 , if m is 1, has one of the meanings as given above for R 1 , R 2 , R 4 and R 5 ; R 3 , if m is 2, is a divalent group; R 6 is hydrogen or C 1 -C 4 alkyl; R 7 is hydrogen, and if R 6 is hydrogen then R 7 may additionally be C 1 -C 4 alkyl; R 8 is group (A) or (B) X is O, O-CH 2 - or -O(CHR 14 )-; n is 0-10; provided that (i) if n is 0, and X is O, then R 8 is a group A; (ii) if n is other than 0, then X is O and R 8 is the group A; R 9 and R 10 independently of one another are hydrogen or C 1 -C 4 alkyl; R 11 and R 12 independently of one another are C 1 -C 4 alkyl or form together with the C atom to which they are attached a 5 to 7 membered saturated carbocyclic ring; R 13 is hydrogen, C 1 -C 4 alkyl, C 5 -C 7 cycloalkyl, 2-tetrahydropyranyl or Si(C 1 -C 4 alkyl) 3 ; R 14 is a group (A'); and R' 13 has one of the meanings as given for R 13 or is the group (C); are effective photoinitiator compounds.