Silyl Glyoximides: Toward a New Class of Visible Light Photoinitiators

Many academic and industrial works are carried out for the search of new classes of visible light photoinitiators. In the last decade, new Type I photoinitiator generating silyl, germyl, or stannyl radicals is elegantly reported; the chemical mechanisms being often associated with the cleavage of the C(O)-Si, C(O)-Ge, or C(O)-Sn bonds. In this context, silyl glyoxylates are also reported as dual Type I and Type II photoinitiators. Silyl glyoximides are proposed here as new near-UV and blue light sensitive photoinitiators. The synthesis of such compounds as well as their light absorption properties is discussed. Their photochemical properties are studied through steady state photolysis experiments and molecular modeling data (i.e., through the calculations of the frontier orbitals, C-C bond dissociation energies and triplet state energy levels). To finish, their photoinitiating ability upon near-UV or blue light emitting diode light is examined in a benchmark methacrylate monomer blend (BisGMA/TEGDMA). Markedly, a Type I photoinitiator behavior is highlighted but better initiating properties are found in multicomponent systems in combination with iodonium salt and amine.