Photolysis mechanism of Di(tert-butylphenyl)iodonium salt using 2-isopropylthioxanthone as a sensitizer

Diaryliodonium salts (Ar₂I⁺X⁻) are used as a photosensitive initiator that generates acid or radical species by ultraviolet light irradiation. Recently, sensitization of Ar₂I⁺X⁻ has gained importance owing to the escalating demand for high-sensitive initiators with longer wavelength absorption such as 365 and 436 nm. However, the mechanism of photolysis of Ar₂I⁺X⁻ has not been strictly elucidated. This paper shows discussions of the details of its mechanism. Herein, we analyzed the photosensitization of Ar₂I⁺X⁻ with 2–isopropylthioxanthone (ITX) based on transient absorption techniques. As a result, it was revealed that electron transfer occurred from a triplet excited state of ITX to Ar₂I⁺X⁻ with an electron transfer rate constant of 4.2 × 10⁹ s⁻¹. Furthermore, high performance liquid chromatography measurements found the quantum yield of the photolysis was determined to be 0.48.