X-ray transient absorption reveals the 1Au (nπ*) state of pyrazine in electronic relaxation

Abstract

Electronic relaxation in organic chromophores often proceeds via states not directly accessible by photoexcitation. We report on the photoinduced dynamics of pyrazine that involves such states, excited by a 267 nm laser and probed with X-ray transient absorption spectroscopy in a table-top setup. In addition to the previously characterized 1B2u (ππ*) (S2) and 1B3u (nπ*) (S1) states, the participation of the optically dark 1Au (nπ*) state is assigned by a combination of experimental X-ray core-to-valence spectroscopy, electronic structure calculations, nonadiabatic dynamics simulations, and X-ray spectral computations. Despite 1Au (nπ*) and 1B3u (nπ*) states having similar energies at relaxed geometry, their X-ray absorption spectra differ largely in transition energy and oscillator strength. The 1Au (nπ*) state is populated in 200 ± 50 femtoseconds after electronic excitation and plays a key role in the relaxation of pyrazine to the ground state.

Ab Initio Quasiclassical Simulation of Femtosecond Time-Resolved Two-Dimensional Electronic Spectra of Pyrazine

“…66,69−71 While Suzuki and co-workers could not find evidence for the intermediate population of the A u state, 66−68 Leone and coworkers reported detection of population in the A u state with a time delay of 200 fs. 69 A recent computational simulation of the TRPES of pyrazine confirmed that the A u population indeed cannot be clearly distinguished from the B 3u population in TRPES. 71 According to quantum dynamics calculations for an ab initio based three-state nine-mode model of pyrazine 65 as well as full-dimensional ab initio quasiclassical SH simulations for pyrazine, 53 the (diabatic) B 3u and A u states are comparably populated already after 50 fs (Figure 2b).…”

“…Pyrazine therefore represents a natural benchmark system for the ab initio simulation of femtosecond time-resolved nonlinear spectra. Experimentally, the photodynamics of pyrazine was studied by Suzuki and co-workers with femtosecond time-resolved photoelectron spectroscopy (TRPES) in the UV − and very recently by Leone and co-workers with femtosecond X-ray absorption spectroscopy . The transient population of the dark A u state in the photophysics of pyrazine has become a controversially discussed topic in the recent literature. ,− While Suzuki and co-workers could not find evidence for the intermediate population of the A u state, − Leone and co-workers reported detection of population in the A u state with a time delay of 200 fs .…”

“…Experimentally, the photodynamics of pyrazine was studied by Suzuki and co-workers with femtosecond time-resolved photoelectron spectroscopy (TRPES) in the UV − and very recently by Leone and co-workers with femtosecond X-ray absorption spectroscopy . The transient population of the dark A u state in the photophysics of pyrazine has become a controversially discussed topic in the recent literature. ,− While Suzuki and co-workers could not find evidence for the intermediate population of the A u state, − Leone and co-workers reported detection of population in the A u state with a time delay of 200 fs . A recent computational simulation of the TRPES of pyrazine confirmed that the A u population indeed cannot be clearly distinguished from the B 3u population in TRPES .…”

Excited state absorption of DNA bases in the gas phase and in chloroform solution: a comparative quantum mechanical study

“…20 MOM-TDDFT (and even MOM-CCSD) is often used to obtain X-ray absorption spectra of valence excited states, i.e. to simulate valence pump-core probe spectra, 21–24 but hardly explored for ESA in the UV-vis region.…”

Core excitations: how far can we push correlated single-reference formalism for Delta-based methods?

“…[2][3][4] As a result, scientists have been able to observe phenomena in chemistry, [5][6][7] material sciences, 8,9 and physics 10,11 that were previously inaccessible. Furthermore, the increasing availability of table-top equipment [12][13][14][15] capable of generating the light required for core spectroscopies has extended the use of said techniques for a variety of new studies. 16 Efficiently and accurately modeling core excited states presents several challenges that a useful methodology should address, chief among them the large charge rearrangement associated with the creation of the core hole.…”