Comparison between NIR and UV-sensitized radical and cationic reactivity of iodonium salts comprising anions with different coordination behavior

Abstract

Substituted diaryliodonium salts bearing weak coordinating anions ([(CF3SO2)3C]-; [(CF3SO2)2N]-; [PF6]-; [PF3(C2F5)3]-; [PF3(n-C4F9)3]-) were tested regarding their efficiency as radical initiator to initiate radical polymerization according to a sensitized mechanism. A NIR LED emitting at 790 nm was applied to initiate sensitized polymerization applying the polymethine S2265 as sensitizer. Change of the sensitizer resulting in spectral overlap with emission of UV-LED emitting at 395 nm complimented the experiments to understand the behavior of these iodonium salts under different exposure conditions. Furthermore, formation of protons was quantitatively probed by Rhodamine B lactone showing that UV sensitization resulted in a significant higher yield compared to NIR-sensitized photopolymerization. Surprisingly, the iodonium salt bearing the [(CF3SO2)3C]--anion exhibited a good performance in both radical photopolymerization and photoinduced formation of protons. Thioxanthon (ITX) served as sensitizer for all UV-LED experiments.