Excited-State Dynamics of a D‑π‑A Type Sulfonium-Based Alkoxystilbene Photoacid Generator

The excited-state relaxation dynamics of a D-π-A sulfonium-based alkoxystilbene photoacid generator has been investigated in acetonitrile solution by using femtosecond transient absorption and nanosecond laser flash photolysis experiments. For the first time, the successive reaction steps involved in the photoinduced proton generation of a sulfonium acid generator have been kinetically and spectrally resolved from the early stages (femtosecond time scale) to the final chemical processes (microsecond domain). An overall four-step reaction scheme is established, and two main deactivation pathways limiting the proton generation efficiency are identified and quantified.