Photoinitiators for free radical polymerization based on the thioxanthone chromophore that contains benzothiophene were synthesized and characterized. Compared to thioxanthone, these compounds show a bathochromic shifted absorption up to similar to 460 nm. High quantum yields for intersystem crossing generate sufficient amounts of triplet states. Initiator radicals are generated by reaction of the triplet states with tertiary amines, such as diethanolamine with high rate constants (2-6 x 10(9)M(-1)s(-1)) as determined by laser flash photolysis. Photoinitiated polymerization experiments of MMA showed efficient polymerization with initiator concentrations as low as 0.1 mM. (C) 2016 Elsevier B.V. All rights reserved.