Compounds of formula (I), wherein R.sub.1 is hydrogen or alkyl; R.sub.2 is C.sub.1-C.sub.4alkoxy or a morpholino radical; and R.sub.3 is hydrogen or C.sub.1-C.sub.4alkoxy, are suitable for improving the solubility of specific photoinitiators in formulations and accordingly enhance the storage stability of formulations comprising a photoinitiator and compounds of formula (I) ##STR00001##