Elucidating the Nature of the Excited State of a Heteroleptic Copper Photosensitizer by using Time-Resolved X-ray Absorption Spectroscopy

Dooshaye Moonshiram, Pablo Garrido-Barros, Carolina Gimbert-Suriñach, Antonio Picón, Cunming Liu, Xiaoyi Zhang, Michael Karnahl, Antoni Llobet

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Abstract

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim We report the light-induced electronic and geometric changes taking place within a heteroleptic CuI photosensitizer, namely [(xant)Cu(Me2phenPh2)]PF6 (xant=xantphos, Me2phenPh2=bathocuproine), by time-resolved X-ray absorption spectroscopy in the ps–μs time regime. Time-resolved X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis enabled the elucidation of the electronic and structural configuration of the copper center in the excited state as well as its decay dynamics in different solvent conditions with and without triethylamine acting as a sacrificial electron donor. A three-fold decrease in the decay lifetime of the excited state is observed in the presence of triethylamine, showing the feasibility of the reductive quenching pathway in the latter case. A prominent pre-edge feature is observed in the XANES spectrum of the excited state upon metal to charge ligand transfer transition, showing an increased hybridization of the 3d states with the ligand p orbitals in the tetrahedron around the Cu center. EXAFS and density functional theory illustrate a significant shortening of the Cu−N and an elongation of the Cu−P bonds together with a decrease in the torsional angle between the xantphos and bathocuproine ligand. This study provides mechanistic time-resolved understanding for the development of improved heteroleptic CuI photosensitizers, which can be used for the light-driven production of hydrogen from water.
Original languageEnglish
Pages (from-to)6464-6472
JournalChemistry - A European Journal
Volume24
Issue number24
DOIs
Publication statusPublished - 25 Apr 2018

Keywords

  • artificial photosynthesis
  • copper heteroleptic photosensitizers
  • electron transfer
  • photocatalysis
  • time-resolved X-ray absorption spectroscopy

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    Moonshiram, D., Garrido-Barros, P., Gimbert-Suriñach, C., Picón, A., Liu, C., Zhang, X., Karnahl, M., & Llobet, A. (2018). Elucidating the Nature of the Excited State of a Heteroleptic Copper Photosensitizer by using Time-Resolved X-ray Absorption Spectroscopy. Chemistry - A European Journal, 24(24), 6464-6472. https://doi.org/10.1002/chem.201800330