Structural dynamics upon photoexcitation-induced charge transfer in a dicopper(i)-disulfide complex
Journal article, 2018
The structural dynamics of charge-transfer states of nitrogen-ligated copper complexes has been extensively investigated in recent years following the development of pump-probe X-ray techniques. In this study we extend this approach towards copper complexes with sulfur coordination and investigate the influence of charge transfer states on the structure of a dicopper(i) complex with coordination by bridging disulfide ligands and additionally tetramethylguanidine units [Cu I 2 (NSSN) 2 ] 2+ . In order to directly observe and refine the photoinduced structural changes in the solvated complex we applied picosecond pump-probe X-ray absorption spectroscopy (XAS) and wide-angle X-ray scattering (WAXS). Additionally, the ultrafast evolution of the electronic excited states was monitored by femtosecond transient absorption spectroscopy in the UV-Vis probe range. DFT calculations were used to predict molecular geometries and electronic structures of the ground and metal-to-ligand charge transfer states with singlet and triplet spin multiplicities, i.e. S 0 , 1 MLCT and 3 MLCT, respectively. Combining these techniques we elucidate the electronic and structural dynamics of the solvated complex upon photoexcitation to the MLCT states. In particular, femtosecond optical transient spectroscopy reveals three distinct timescales of 650 fs, 10 ps and > 100 ps, which were assigned as internal conversion to the ground state (S n → S 0 ), intersystem crossing 1 MLCT → 3 MLCT, and subsequent relaxation of the triplet to the ground state, respectively. Experimental data collected using both X-ray techniques are in agreement with the DFT-predicted structure for the triplet state, where coordination bond lengths change and one of the S-S bridges is cleaved, causing the movement of two halves of the molecule relative to each other. Extended X-ray absorption fine structure spectroscopy resolves changes in Cu-ligand bond lengths with precision on the order of 0.01 Å, whereas WAXS is sensitive to changes in the global shape related to relative movement of parts of the molecule. The results presented herein widen the knowledge on the electronic and structural dynamics of photoexcited copper-sulfur complexes and demonstrate the potential of combining the pump-probe X-ray absorption and scattering for studies on photoinduced structural dynamics in copper-based coordination complexes.
Author
M. Naumova
Padernborn University
University of Hamburg
Deutsches Elektronen-Synchrotron (DESY)
Dmitry Khakhulin
European XFEL
University of Hamburg
Mateusz Rebarz
Czech Academy of Sciences
Martin Rohrmüller
Padernborn University
B. Dicke
University of Hamburg
Deutsches Elektronen-Synchrotron (DESY)
M. Biednov
Deutsches Elektronen-Synchrotron (DESY)
University of Hamburg
Alexander Britz
European XFEL
University of Hamburg
Shirly Espinoza
Czech Academy of Sciences
B. Grimm-Lebsanft
University of Hamburg
Deutsches Elektronen-Synchrotron (DESY)
Miroslav Kloz
Czech Academy of Sciences
Norman Kretzschmar
European Synchrotron Radiation Facility (ESRF)
Adam Neuba
Padernborn University
Jochen Ortmeyer
Max Planck Society
Padernborn University
Roland Schoch
Padernborn University
Jakob Andreasson
Czech Academy of Sciences
Uppsala University
Chalmers, Physics, Condensed Matter Physics
Matthias Bauer
Padernborn University
C. Bressler
University of Hamburg
European XFEL
Wolf Gero Schmidt
Padernborn University
Gerald Henkel
Padernborn University
M. Rübhausen
Deutsches Elektronen-Synchrotron (DESY)
University of Hamburg
Physical Chemistry Chemical Physics
1463-9076 (ISSN) 1463-9084 (eISSN)
Vol. 20 9 6274-6286Subject Categories
Inorganic Chemistry
Atom and Molecular Physics and Optics
Theoretical Chemistry
DOI
10.1039/c7cp04880g
PubMed
29431759