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Tracing the Full Bimolecular Photocycle of Iron(III)-Carbene Light Harvesters in Electron-Donating Solvents

Rosemann, Nils W. LU ; Chábera, Pavel LU ; Prakash, Om LU ; Kaufhold, Simon LU ; Wärnmark, Kenneth LU ; Yartsev, Arkady LU and Persson, Petter LU (2020) In Journal of the American Chemical Society 142(19). p.8565-8569
Abstract

Photoinduced bimolecular charge transfer processes involving the iron(III) N-heterocyclic carbene (FeNHC) photosensitizer [Fe(phtmeimb)2]+ (phtmeimb = phenyltris(3-methyl-imidazolin-2-ylidene)borate) and triethylamine as well as N,N-dimethylaniline donors have been studied using optical spectroscopy. The full photocycle of charge separation and recombination down to ultrashort time scales was studied by investigating the excited-state dynamics up to high quencher concentrations. The unconventional doublet ligand-to-metal charge transfer (2LMCT) photoactive excited state exhibits donor-dependent charge separation rates of up to 1.25 ps-1 that exceed the rates found for typical ruthenium-based systems and are instead more similar to... (More)

Photoinduced bimolecular charge transfer processes involving the iron(III) N-heterocyclic carbene (FeNHC) photosensitizer [Fe(phtmeimb)2]+ (phtmeimb = phenyltris(3-methyl-imidazolin-2-ylidene)borate) and triethylamine as well as N,N-dimethylaniline donors have been studied using optical spectroscopy. The full photocycle of charge separation and recombination down to ultrashort time scales was studied by investigating the excited-state dynamics up to high quencher concentrations. The unconventional doublet ligand-to-metal charge transfer (2LMCT) photoactive excited state exhibits donor-dependent charge separation rates of up to 1.25 ps-1 that exceed the rates found for typical ruthenium-based systems and are instead more similar to results reported for organic sensitizers. The ultrafast charge transfer probed at high electron donor concentrations outpaces the solvent dynamics and goes beyond the classical Marcus electron transfer regime. Poor photoproduct yields are explained by donor-independent, fast charge recombination with rates of ∼0.2 ps-1, thus inhibiting cage escape and photoproduct formation. This study thus shows that the ultimate bottlenecks for bimolecular photoredox processes involving these FeNHC photosensitizers can only be determined from the ultrafast dynamics of the full photocycle, which is of particular importance when the bimolecular charge transfer processes are not limited by the intrinsic excited-state lifetime of the photosensitizer.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of the American Chemical Society
volume
142
issue
19
pages
5 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • pmid:32307993
  • scopus:85088253350
ISSN
0002-7863
DOI
10.1021/jacs.0c00755
language
English
LU publication?
yes
id
0c416cb2-e19e-443f-b6cd-f3f10227a6b3
date added to LUP
2021-01-18 05:20:11
date last changed
2021-04-06 04:02:24
@article{0c416cb2-e19e-443f-b6cd-f3f10227a6b3,
  abstract     = {<p>Photoinduced bimolecular charge transfer processes involving the iron(III) N-heterocyclic carbene (FeNHC) photosensitizer [Fe(phtmeimb)2]+ (phtmeimb = phenyltris(3-methyl-imidazolin-2-ylidene)borate) and triethylamine as well as N,N-dimethylaniline donors have been studied using optical spectroscopy. The full photocycle of charge separation and recombination down to ultrashort time scales was studied by investigating the excited-state dynamics up to high quencher concentrations. The unconventional doublet ligand-to-metal charge transfer (2LMCT) photoactive excited state exhibits donor-dependent charge separation rates of up to 1.25 ps-1 that exceed the rates found for typical ruthenium-based systems and are instead more similar to results reported for organic sensitizers. The ultrafast charge transfer probed at high electron donor concentrations outpaces the solvent dynamics and goes beyond the classical Marcus electron transfer regime. Poor photoproduct yields are explained by donor-independent, fast charge recombination with rates of ∼0.2 ps-1, thus inhibiting cage escape and photoproduct formation. This study thus shows that the ultimate bottlenecks for bimolecular photoredox processes involving these FeNHC photosensitizers can only be determined from the ultrafast dynamics of the full photocycle, which is of particular importance when the bimolecular charge transfer processes are not limited by the intrinsic excited-state lifetime of the photosensitizer. </p>},
  author       = {Rosemann, Nils W. and Chábera, Pavel and Prakash, Om and Kaufhold, Simon and Wärnmark, Kenneth and Yartsev, Arkady and Persson, Petter},
  issn         = {0002-7863},
  language     = {eng},
  number       = {19},
  pages        = {8565--8569},
  publisher    = {The American Chemical Society (ACS)},
  series       = {Journal of the American Chemical Society},
  title        = {Tracing the Full Bimolecular Photocycle of Iron(III)-Carbene Light Harvesters in Electron-Donating Solvents},
  url          = {http://dx.doi.org/10.1021/jacs.0c00755},
  doi          = {10.1021/jacs.0c00755},
  volume       = {142},
  year         = {2020},
}