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

Abstract

Picosecond X-ray absorption (XA) spectroscopy at the S K-edge (∼2.4 keV) is demonstrated and used to monitor excited state dynamics in a small organosulfur molecule (2-Thiopyridone, 2TP) following optical excitation. Multiple studies have reported that the thione (2TP) is converted into the thiol (2-Mercaptopyridine, 2MP) following photoexcitation. However, the timescale and photochemical pathway of this reaction remain uncertain. In this work, time-resolved XA spectroscopy at the S K-edge is used to monitor the formation and decay of two transient species following 400 nm excitation of 2TP dissolved in acetonitrile. The first transient species forms within the instrument response time (70 ps) and decays within 6 ns. The second transient species forms on a timescale of ∼400 ps and decays on a 15 ns timescale. Time-dependent density functional theory is used to identify the first and second transient species as the lowest-lying triplet states of 2TP and 2MP, respectively. This study demonstrates transient S K-edge XA spectroscopy as a sensitive and viable probe of time-evolving charge dynamics near sulfur sites in small molecules with future applications towards studying complex biological and material systems.

Probing competing relaxation pathways in malonaldehyde with transient X-ray absorption spectroscopy

“…The simulated TRXAS signals for the two ICs provide clear signatures that enable ngerprinting the competing internal conversion channels, including population transfer mediated by the HTI. While time-resolved K-edge absorption has previously been used to discriminate reactant and product of photoinduced tautomerization using a synchrotron source (time resolution of $70 ps), 106 high temporal resolution is key in the present case.…”

Chemical interactions and dynamics with femtosecond X-ray spectroscopy and the role of X-ray free-electron lasers

“…Areas that are not covered here include time-resolved X-ray probing of 4d and 5d metal systems [2] and of materials for solar energy conversion [2,3], time-resolved X-ray spectroscopy of small molecules and organic systems in solution probing C, N, O and S K-edges [11][12][13], surface chemical reactions [14][15][16], femto-, pico-and nanosecond time-resolved X-ray spectroscopy at synchrotron radiation X-ray sources [2,3,[17][18][19][20][21][22][23][24], and time-resolved X-ray scattering of photochemical reactions in solution [25][26][27][28][29][30][31] and in the gas phase [32,33].…”

Ultrafast Intersystem Crossing in Acetylacetone via Femtosecond X-ray Transient Absorption at the Carbon K-Edge

“…[25][26] Thus, when combined with time-resolved detection, the evolving near-edge coreto-valence spectral features report accurately on the changes in the electronic charge distributions, oxidation states, chemical environments, and spin crossover of the photoexcited molecule with atomic site specificity. 19,[27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] Further, the large energy separations between the absorption edges of different elements (tens to hundreds of eV) and the encoding of the nearedge spectral region by a few predominant core-to-valence transitions offer easy spectral elucidation in comparison to valence state photoionization spectroscopies, which may produce broad and overlapping spectral signatures from multiple photoionization channels. 42 The high photon energies and bandwidth of the x-ray probe allows monitoring large amplitude nuclear motions on multiple electronic states, making core-level spectroscopy generally sensitive to geometrical parameters and charge states.…”