Thioxanthone-functionalized 1,6-heptadiene as monomeric photoinitiator

The synthesis of the first photoinitiator (PI) based on thioxanthone (TX) with 1,6-heptadiene structure is described. This PI (TXdMA) absorbs in the near UV-vis region (435-439 rim; with absorption redshift approximate to 50 nm and e values comparable to TX). Photopolymerization results demonstrate that although TXdMA is not an effective one-component polymerizable photoinitiator, it can successfully initiate photopolymerization of poly(ethylene glycol) diacrylate (PEGDA, M-n = 250 D) and trimethylolpropane triacrylate (TMPTA) in the presence of bis-(4-tert-butylphenyl)-iodonium hexafluorophosphate (Iod) similar to TX/Iod. TXdMA exhibits better migration stability than TX. Absorption, fluorescence, steady state photolysis and cyclic voltammetry experiments are carried out to investigate the photochemical mechanisms.