Compounds of formula I ##STR1## wherein R.sub.1, R.sub.2, and R.sub.3 independently of one another are hydrogen; C.sub.1 -C.sub.20 alkyl which is unsubstituted or substituted by OH, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkylthio, phenylthio, F, Cl, Br, I, CN, (C.sub.1 -.sub.8 alkyl)O--(CO)--, (C.sub.1 -C.sub.4 alkyl)--(CO)O-- or/and di(C.sub.1 -C.sub.4 alkyl)amino; or R.sub.1, R.sub.2, and R.sub.3 independently of one another are C.sub.3 -C.sub.6 alkenyl; phenyl which is unsubstituted or substituted by OH, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkylthio, phenylthio, F, Cl, Br, I, CN, (C.sub.1 -C.sub.8 alkyl)O(CO)--, (C.sub.1 -C.sub.4 alkyl)--(CO)O-- or/-- and di(C.sub.1 -C.sub.4 alkyl)amino; or R.sub.1 and R.sub.2 together are C.sub.2 -C.sub.9 alkylene, o-xylylene, 2-butenylene, C.sub.3 -C.sub.9 oxaalkylene or C.sub.3 -C.sub.9 azaalkylene; R.sub.4, R.sub.5, R.sub.6, and R.sub.7 independently of one another are sec-C.sub.3 -C.sub.20 alkyl, tert-C.sub.4 -C.sub.20 alkyl or phenyl wherein these radicals are unsubstituted or substituted by OH, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkylthio, phenylthio, F, Cl, Br, I, CN, (C.sub.1 -C.sub.8 alkyl)O(CO)--, (C.sub.1 -C.sub.4 alkyl)--(CO)O-- or/and di(C.sub.1 -C.sub.4 alkyl)amino; or R.sub.4 and R.sub.5, and/or R.sub.6 and R.sub.7 together are C.sub.2 -C.sub.9 alkylene, o-xylylene, 2-butenylene, C.sub.3 -C.sub.9 oxaalkylene or C.sub.3 -C.sub.9 azaalkylene, or R.sub.4 and R.sub.6, and/or R.sub.5 and R.sub.7 together are branched C.sub.2 -C.sub.9 alkylene, o-xylylene, 2-butenylene, C.sub.3 -C.sub.9 oxaalkylene or C.sub.3 -C.sub.9 azaalkylene; are suitable as photoinitiators for the photopolymerization of unsaturated compounds.