The invention relates to novel photoinitiators of formula (I) wherein A is --O--, --CH.sub.2-, CH(CH.sub.3)-- or --C(CH.sub.3).sub.2-, and R is methyl or trimethylsilyl, and R may in addition be hydrogen when A is simultaneously the group --C(CH.sub.3).sub.2-. The invention relates also to compositions comprising (A) at least one ethylenically unsaturated compound, (B) a photoinitiator of formula (I), (C) optionally further binders or additives, (D) optionally further photoinitiators or co-initiators. Compositions comprising (A) an ethylenically unsaturated compound that contains at least one aminoacrylate, (B) a photoinitiator of formula (II) or (III), (C) optionally further binders or additives, (D) optionally further photoinitiators or co-initiators. ##STR00001##