Photophysical Investigations on Photoinitiators with Covalently Linked Thioxanthone Sensitizer Moieties

The photophysical properties of three photoinitiators with a covalently linked thioxanthone sensitizer unit absorbing up to 410 nm were investigated by laser‐flash photolysis and CIDNP spectroscopy. These complementary techniques revealed two competing reaction pathways of the molecular dyads 1 – 3 : i ) triplet‐energy transfer from the sensitizer to the morpholine moiety followed by α ‐cleavage to yield a radical pair, which initiates radical polymerization, and ii ) bimolecular electron transfer from the morpholine to the thioxanthone subunit followed by proton transfer. The relative efficiency of these routes is determined by the triplet energy of the photoinitiator moiety relative to that of the sensitizer.