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.
Highlights
Introduction published maps and institutional affilSir George Porter stated in his Nobel prize lecture [1] that “ . . . since each molecule has only one ground state, but several excited states, it is clear that this field of investigation is, in principle, a bigger subject than the whole of conventional chemistry . . . ” This statement was based on his work on flash photolysis [2] using flash lamps as well as first available lasers with pulse durations in the nanosecond range
An intense short laser pulse hits a solid target in vacuum and creates a plasma that emits soft X-ray radiation (SXR)
In order to meet different requirements concerning achievable time and spectral structure of the SXR radiation, we have developed two laser-produced plasma sources (LPP) sources enabling state-of-the-art near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in the laboratory
Summary
Avogadro an isosurface value of 0.01. Avogadro withwith an isosurface value of 0.01. 1. It 1. positive) are mainly located at the site of the carbon rings and less at the alkyl positive) are mainly located at the site of the carbon rings and less at the alkyl substituent, substituent, which for is common for such organic compounds with systems. conjugated systems. Figure 1.
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