A Charge-Transfer Complex of Thioxanthonephenacyl Sulfonium Salt as a Visible-Light Photoinitiator for Free Radical and Cationic Polymerizations

A new double chromophoric sulfonium salt photoinitiator possessing both thioxanthone and phenacyl groups, namely 2-isopropylthioxanthonium phenacyl hexafluoroantimonate (ITXPhenS), was synthesized and characterized. ITXPhenS can form a charge-transfer complex (CTC) with the donor N,N-dimethyl aniline (DMA) with absorption characteristics in the visible range as confirmed by spectral analysis, cyclic voltammetry (CV) and density functional theory (DFT). The extension of the absorbance shift can be controlled by the ITXPhenS to DMA ratio. The ability of the CTC to initiate free radical and cationic polymerization reactions of various monomers under visible and natural sunlight is demonstrated. The proposed mechanism assumes the generation of radical and ionic species by the heterolytic and/or homolytic cleavage of ITXPhenS within the CTC followed by electron-transfer reactions.