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Captivating bimolecular photoredox dynamics of a ligand-to-metal charge transfer complex

Wegeberg, Christina LU ; Calvet, Neus A. LU orcid ; Krafft, Mila LU ; Chábera, Pavel LU ; Yartsev, Arkady LU orcid and Persson, Petter LU (2025) In Chemical Science 16(46). p.21975-21990
Abstract
Transition metal complexes featuring ligand-to-metal charge transfer (LMCT) excited states have been identified as promising candidates for driving electron transfer processes. To obtain an efficient system based on photo-induced bimolecular electron transfer, it is required that (1) photo-induced charge separation (CS) is faster than charge recombination (CR) of the separated charges, and (2) CR is slower than their spatial separation via cage escape (CE). Here, we investigate this competitive sequence of processes by the photocycle of a rhenium(II) complex featuring a strongly oxidizing 2LMCT excited state. Intrinsic CS and CR rates were measured up to multimolar concentrations for several electron donors to elucidate... (More)
Transition metal complexes featuring ligand-to-metal charge transfer (LMCT) excited states have been identified as promising candidates for driving electron transfer processes. To obtain an efficient system based on photo-induced bimolecular electron transfer, it is required that (1) photo-induced charge separation (CS) is faster than charge recombination (CR) of the separated charges, and (2) CR is slower than their spatial separation via cage escape (CE). Here, we investigate this competitive sequence of processes by the photocycle of a rhenium(II) complex featuring a strongly oxidizing 2LMCT excited state. Intrinsic CS and CR rates were measured up to multimolar concentrations for several electron donors to elucidate both the diffusion-controlled and close-contact regimes over a wide range of thermodynamic driving forces. Ultrafast dynamics (<200 fs) suggest that CS is dominated by a hot electron transfer component competing with 2LMCT vibrational relaxations in the high-concentration/close-contact regime. The intrinsic CS and CR rates related to the relaxed 2LMCT state dominate the dynamics at intermediate concentrations and show concentration-dependence at 3–50 vol% electron donor concentration and concentration-independence at higher concentrations with τCS = 0.5 ps and τCR = 2 ps, for the prototype donor anisole. The ratio between CS and CR rates was altered systematically by the thermodynamic driving force of electron transfer, utilizing the fact that the processes lie in the Marcus normal and inverted regions, respectively, and with deviations from classical Marcus behavior accounted for by using Marcus–Jortner–Levich theory. Our findings provide unique insight into the complex competition between kinetic factors controlling the fundamental dynamics of the charge-separated pairs inside the solvent cage for photocycles driven by 2LMCT excited states. (Less)
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author
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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Chemical Science
volume
16
issue
46
pages
16 pages
publisher
Royal Society of Chemistry
external identifiers
  • scopus:105022928147
  • pmid:41122472
ISSN
2041-6520
DOI
10.1039/d5sc03839a
language
English
LU publication?
yes
additional info
Publisher Copyright: This journal is © The Royal Society of Chemistry
id
c2839862-03f5-4f1c-9050-e07eee296795
date added to LUP
2025-12-02 09:26:59
date last changed
2025-12-05 03:46:11
@article{c2839862-03f5-4f1c-9050-e07eee296795,
  abstract     = {{Transition metal complexes featuring ligand-to-metal charge transfer (LMCT) excited states have been identified as promising candidates for driving electron transfer processes. To obtain an efficient system based on photo-induced bimolecular electron transfer, it is required that (1) photo-induced charge separation (CS) is faster than charge recombination (CR) of the separated charges, and (2) CR is slower than their spatial separation <em>via</em> cage escape (CE). Here, we investigate this competitive sequence of processes by the photocycle of a rhenium(II) complex featuring a strongly oxidizing <sup>2</sup>LMCT excited state. Intrinsic CS and CR rates were measured up to multimolar concentrations for several electron donors to elucidate both the diffusion-controlled and close-contact regimes over a wide range of thermodynamic driving forces. Ultrafast dynamics (&lt;200 fs) suggest that CS is dominated by a hot electron transfer component competing with <sup>2</sup>LMCT vibrational relaxations in the high-concentration/close-contact regime. The intrinsic CS and CR rates related to the relaxed <sup>2</sup>LMCT state dominate the dynamics at intermediate concentrations and show concentration-dependence at 3–50 vol% electron donor concentration and concentration-independence at higher concentrations with <em>τ</em><sub>CS</sub> = 0.5 ps and <em>τ</em><sub>CR</sub> = 2 ps, for the prototype donor anisole. The ratio between CS and CR rates was altered systematically by the thermodynamic driving force of electron transfer, utilizing the fact that the processes lie in the Marcus normal and inverted regions, respectively, and with deviations from classical Marcus behavior accounted for by using Marcus–Jortner–Levich theory. Our findings provide unique insight into the complex competition between kinetic factors controlling the fundamental dynamics of the charge-separated pairs inside the solvent cage for photocycles driven by <sup>2</sup>LMCT excited states.}},
  author       = {{Wegeberg, Christina and Calvet, Neus A. and Krafft, Mila and Chábera, Pavel and Yartsev, Arkady and Persson, Petter}},
  issn         = {{2041-6520}},
  language     = {{eng}},
  month        = {{10}},
  number       = {{46}},
  pages        = {{21975--21990}},
  publisher    = {{Royal Society of Chemistry}},
  series       = {{Chemical Science}},
  title        = {{Captivating bimolecular photoredox dynamics of a ligand-to-metal charge transfer complex}},
  url          = {{http://dx.doi.org/10.1039/d5sc03839a}},
  doi          = {{10.1039/d5sc03839a}},
  volume       = {{16}},
  year         = {{2025}},
}