This invention relates to a photoinitiator compound comprising: a polyhedral oligomeric silsesquioxane (POSS) moiety and a photoinitiator moiety, wherein the photoinitiator compound having the structure according to formula (I): [R—SiO1.5]n (I), wherein n is 6, 8, 10 or 12 and R is independently selected from the group consisting of H, linear or branched (hetero)alkyl, linear or branched (hetero)alkenyl, (hetero)aryl, (hetero)alkyl aryl, (hetero)aryl alkyl and a photoinitiator moiety, wherein at least one R is a photoinitiator moiety and the photoinitiator compound is a nanoparticle. The present invention also relates to a method for the production of the photoinitiator compound of the invention, a photopolymerizable composition comprising the photoinitiator compound of the invention, the use of the photoinitiator compound of the invention for photopolymerization. The present invention is further related to a coated substrate comprising the photopolymerizable composition of the invention.