Light-Induced Radical Formation and Isomerization of an Aromatic Thiol in Solution Followed by Time-Resolved X-ray Absorption Spectroscopy at the Sulfur K-Edge

Abstract

We applied time-resolved sulfur-1s absorption spectroscopy to a model aromatic thiol system as a promising method for tracking chemical reactions in solution. Sulfur-1s absorption spectroscopy allows tracking multiple sulfur species with a time resolution of ∼70 ps at synchrotron radiation facilities. Experimental transient spectra combined with high-level electronic structure theory allow identification of a radical and two thione isomers, which are generated upon illumination with 267 nm radiation. Moreover, the regioselectivity of the thione isomerization is explained by the resulting radical frontier orbitals. This work demonstrates the usefulness and potential of time-resolved sulfur-1s absorption spectroscopy for tracking multiple chemical reaction pathways and transient products of sulfur-containing molecules in solution.

UV-photochemistry of the biologically relevant thiol group and the disulfide bond: Evolution of early photoproducts from picosecond X-ray absorption spectroscopy at the sulfur K-Edge

“…Homolytic bond cleavage of the S-H group produces arylthiyl and hydrogen radicals upon UV illumination and a signature of another transient photoproduct which emerges within the first 50 ps and coincides with a partial decay of the thiyl radical population. While these studies where not fully conclusive towards identifying the secondary photoproduct, sulfur-!s transitions show the transient XAS signature of the arylthiyl radical I and unambiguously identify the secondary photoproduct as the two thione isomers 2a and 2b of the parent molecule 1, in support of the interpretations of previous work [4]. Fig.…”

Time-resolved soft X-ray absorption spectroscopy in transmission mode on liquids at MHz repetition rates

“…In recent years, NEXAFS has also been used in pump-probe schemes to detect transient electronic and structural configurations 2–10 . Direct access to X-ray absorption cross-sections of the investigated sample material is available in a transmission geometry, which is not the case for low yield fluorescence or surface sensitive electron yield detection schemes.…”

Picosecond sulfur K-edge X-ray absorption spectroscopy with applications to excited state proton transfer

“…Ultrafast XA and emission spectroscopies at the O and N K-edges have been used to study hydrogen bonding dynamics, proton transfer, and spin crossover phenomena 18–21 . Recently, S K-edge spectroscopy at a specific time-delay has been applied to identify photoproducts following the photoexcitation of an aromatic thiol 22 . In this work, we extend time-resolved S K-edge spectroscopy to identify the formation and follow the dynamics of multiple photoproducts during an excited state proton transfer (ESPT) reaction in the solution.…”