Compounds of formula I Y is, for example, C3-C12alkylene, butenylene, butynylene, or C4-C12alkylene interrupted one or more times by non-consecutive —O— or —NR2—; R1 is a reactive group selected from OH, SH, NR3R4, —(CO)—OH, —(CO)—NH2, SO3H, —C(R5)═CR6R7, oxiranyl, —O—(CO)—NH—R8—NCO and —O—(CO)—R9—(CO)—X; R2 is hydrogen, C1-C4alkyl or C2-C4hydroxyalkyl; R3 and R4 are each independently of the other hydrogen, C1-C4alkyl or C2-C4hydroxyalkyl; R5, R6 and R7 are each independently of the others hydrogen or methyl; R8 is, for example, linear or branched C4-C12alkylene, or phenylene; R9 is, for example, linear or branched C1-C16alkylene, —CH═CH—, —CH═CH—CH2—, C6-cycloalkylene, phenylene or naphthylene; and X, X1 and X2 are each independently of the others OH, Cl, OCH3 or OC2H5; are suitable as photoinitiators that can be incorporated in a formulation to be cured.