A use of compounds of the following formula (I) as photoinitiators or photosensitizers in a photopolymerizable composition: wherein R 1 represents a monovalent, linear, branched or cyclic aliphatic hydrocarbon residue having 1 to 20 carbon atoms, which is optionally interrupted by one or more heteroatoms selected from -O- and -NR 2 - and which is optionally substituted with one or more substitutes selected from -Cl, -Br, -OH, =O, -NH-CO-OR 2 , -NH-CO-R 2 and free-radically or ionically polymerizable moieties, wherein the residues R 2 are each independently selected from -H and C 1-6 alkyl; n is ≥ 1, wherein i) if n = 1, Z and Y are not present and X represents -OR 3 ; and ii) if n is > 1, Z represents -OR 4 -, Y represents -OR 5 -, and X represents -H or -OH; wherein R 3 represents -H or one of the options mentioned for R 1 ; and R 4 and R 5 each independently represent a bivalent hydrocarbon residue, for which otherwise the same options apply as for R 1 ; wherein the polymerizable moieties as optional substituents of R 1 are selected from polymerizable double or triple bonds as well as from lactam, lactone, and epoxide moieties, which are subjectable to ring-opening polymerization; and wherein any two of the residues R 1 to R 5 may be optionally linked to each other to form a ring or a dimer; with the proviso that the compound of formula (I) is not 2-oxopropionic acid ethyl ester . R 1 represents a monovalent, linear, branched or cyclic aliphatic hydrocarbon residue having 1 to 20 carbon atoms, which is optionally interrupted by one or more heteroatoms selected from -O- and -NR 2 - and which is optionally substituted with one or more substitutes selected from -Cl, -Br, -OH, =O, -NH-CO-OR 2 , -NH-CO-R 2 and free-radically or ionically polymerizable moieties, wherein the residues R 2 are each independently selected from -H and C 1-6 alkyl; n is ≥ 1, wherein i) if n = 1, Z and Y are not present and X represents -OR 3 ; and ii) if n is > 1, Z represents -OR 4 -, Y represents -OR 5 -, and X represents -H or -OH; wherein R 3 represents -H or one of the options mentioned for R 1 ; and R 4 and R 5 each independently represent a bivalent hydrocarbon residue, for which otherwise the same options apply as for R 1 ; i) if n = 1, Z and Y are not present and X represents -OR 3 ; and ii) if n is > 1, Z represents -OR 4 -, Y represents -OR 5 -, and X represents -H or -OH; wherein R 3 represents -H or one of the options mentioned for R 1 ; and R 4 and R 5 each independently represent a bivalent hydrocarbon residue, for which otherwise the same options apply as for R 1 ; R 3 represents -H or one of the options mentioned for R 1 ; and R 4 and R 5 each independently represent a bivalent hydrocarbon residue, for which otherwise the same options apply as for R 1 ; wherein the polymerizable moieties as optional substituents of R 1 are selected from polymerizable double or triple bonds as well as from lactam, lactone, and epoxide moieties, which are subjectable to ring-opening polymerization; and wherein any two of the residues R 1 to R 5 may be optionally linked to each other to form a ring or a dimer; with the proviso that the compound of formula (I) is not 2-oxopropionic acid ethyl ester . <EOS>