Towards Understanding Excited-State Properties of Organic Molecules Using Time-Resolved Soft X-ray Absorption Spectroscopy

Abstract

The extension of the pump-probe approach known from UV/VIS spectroscopy to very short wavelengths together with advanced simulation techniques allows a detailed analysis of excited-state dynamics in organic molecules or biomolecular structures on a nanosecond to femtosecond time level. Optical pump soft X-ray probe spectroscopy is a relatively new approach to detect and characterize optically dark states in organic molecules, exciton dynamics or transient ligand-to-metal charge transfer states. In this paper, we describe two experimental setups for transient soft X-ray absorption spectroscopy based on an LPP emitting picosecond and sub-nanosecond soft X-ray pulses in the photon energy range between 50 and 1500 eV. We apply these setups for near-edge X-ray absorption fine structure (NEXAFS) investigations of thin films of a metal-free porphyrin, an aggregate forming carbocyanine and a nickel oxide molecule. NEXAFS investigations have been carried out at the carbon, nitrogen and oxygen K-edge as well as on the Ni L-edge. From time-resolved NEXAFS carbon, K-edge measurements of the metal-free porphyrin first insights into a long-lived trap state are gained. Our findings are discussed and compared with density functional theory calculations.

Broadband Time-Delay and Chirp Compensator for X-ray Pulses

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Heteronuclear dual-metal atom catalysts for nanocatalytic tumor therapy

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Toward a fully coherent tender and hard X-ray free-electron laser via cascaded EEHG in fourth-generation synchrotron light sources

“…the NSLS-II upgrade and DL-SLS in PEP tunnel). This FEL-based cascaded EEHG offers improved longitudinal coherence, output stability and time-resolved capability, and extends the spectral range to tender and hard X-ray wavelengths; thus, it can potentially broaden the scientific horizon via studying excited-state dynamics in organic molecules, allowing a greater understanding of the excited-state behavior of complex organic molecules (Stiel et al, 2021;Segatta et al, 2020). Furthermore, taking into account a hypothetical example of a ring with much longer straight sections, we make a side-by-side comparison among two standard SR-based FEL options: prebunching and selfamplified spontaneous emission (SASE).…”