TY - JOUR
T1 - High-Spin State of a Ferrocene Electron Donor Revealed by Optical and X-ray Transient Absorption Spectroscopy
AU - Burke, John H.
AU - Bae, Dae Young
AU - Wallick, Rachel F.
AU - Dykstra, Conner P.
AU - Rossi, Thomas C.
AU - Smith, Laura E.
AU - Leahy, Clare A.
AU - Schaller, Richard D.
AU - Mirica, Liviu M.
AU - Vura-Weis, Josh
AU - van der Veen, Renske M.
N1 - This material is based upon work supported by the Air Force Office of Scientific Research under AFOSR Award no. FA9550-23-1-0368 to J.V.W. This work is part of the National Science Foundation Graduate Research Fellowship Program under Grant no. DGE21-46756 (J.H.B.). J.H.B. acknowledges support from the Robert C. and Carolyn J. Springborn Endowment for Student Support Program. This work was supported by a Packard Fellowship in Science and Engineering from the David and Lucile Packard Foundation (RMvdV, R.F.W.) and by NSF CHE-2155160 (L.M.M., D.Y.B.). R.M.V. acknowledges funding by the Initiative and Networking Fund of the Helmholtz Association. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Awards Number DE-SC0018904 (L.M.M., R.F.W.) and DE-SC0021062 (CD). The authors thank Brandon Rasmussen for help in calculating Fe 1s pre-edge TD-DFT spectra. JHB acknowledges Samuel Pettorini and Roderick Thompson for help in calculating bond-length changes in the excited-state EXAFS model. The authors acknowledge the use of facilities and instrumentation at the Materials Research Laboratory Central Research Facilities, University of Illinois, partially supported by NSF through the University of Illinois Materials Research Science and Engineering Center DMR-1720633. Work performed at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, was supported by the U.S. DOE, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract no. DE-AC02-06CH11357. We would like to thank Xiaoyi Zhang, Richard Spence, Burak Guzelturk, and Jin Yu for invaluable assistance during the experiment.
AFOSR award no. FA9550-23-1-0368 NSF GRFP grant no. DGE21-46756 NSF CHE-2155160 NSF DMR-1720633 DOE award number DE-SC0018904 DOE award number DE-SC0021062 DOE contract number DE-AC02-06CH11357 David and Lucile Packard Foundation Robert C. and Carolyn J. Springborn Endowment for Student Support Program Initiative and Networking Fund of the Helmholtz Association.
PY - 2024/8/7
Y1 - 2024/8/7
N2 - Ferrocene is one of the most common electron donors, and mapping its ligand-field excited states is critical to designing donor-acceptor (D-A) molecules with long-lived charge transfer states. Although 3(d-d) states are commonly invoked in the photophysics of ferrocene complexes, mention of the high-spin 5(d-d) state is scarce. Here, we provide clear evidence of 5(d-d) formation in a bimetallic D-A molecule, ferrocenyl cobaltocenium hexafluorophosphate ([FcCc]PF6). Femtosecond optical transient absorption (OTA) spectroscopy reveals two distinct electronic excited states with 30 and 500 ps lifetimes. Using a combination of ultraviolet, visible, near-infrared, and short-wave infrared probe pulses, we capture the spectral features of these states over an ultrabroadband range spanning 320 to 2200 nm. Time-dependent density functional theory (DFT) calculations of the lowest triplet and quintet states, both primarily Fe(II) (d-d) in character, qualitatively agree with the experimental OTA spectra, allowing us to assign the 30 ps state as the 3(d-d) state and the 500 ps state as the high-spin 5(d-d) state. To confirm the ferrocene-centered high-spin character of the 500 ps state, we performed X-ray transient absorption (XTA) spectroscopy at the Fe and Co K edges. The Fe K-edge XTA spectrum at 150 ps shows a red shift of the absorption edge that is consistent with an Fe(II) high-spin state, as supported by ab initio calculations. The transient signal detected at the Co K-edge is 50× weaker, confirming the ferrocene-centered character of the excited state. Fitting of the transient extended X-ray absorption fine structure region yields an Fe-C bond length increase of 0.25 ± 0.1 Å in the excited state, as expected for the high-spin state based on DFT. Altogether, these results demonstrate that the high-spin state of ferrocene should be considered when designing donor-acceptor assemblies for photocatalysis and photovoltaics.
AB - Ferrocene is one of the most common electron donors, and mapping its ligand-field excited states is critical to designing donor-acceptor (D-A) molecules with long-lived charge transfer states. Although 3(d-d) states are commonly invoked in the photophysics of ferrocene complexes, mention of the high-spin 5(d-d) state is scarce. Here, we provide clear evidence of 5(d-d) formation in a bimetallic D-A molecule, ferrocenyl cobaltocenium hexafluorophosphate ([FcCc]PF6). Femtosecond optical transient absorption (OTA) spectroscopy reveals two distinct electronic excited states with 30 and 500 ps lifetimes. Using a combination of ultraviolet, visible, near-infrared, and short-wave infrared probe pulses, we capture the spectral features of these states over an ultrabroadband range spanning 320 to 2200 nm. Time-dependent density functional theory (DFT) calculations of the lowest triplet and quintet states, both primarily Fe(II) (d-d) in character, qualitatively agree with the experimental OTA spectra, allowing us to assign the 30 ps state as the 3(d-d) state and the 500 ps state as the high-spin 5(d-d) state. To confirm the ferrocene-centered high-spin character of the 500 ps state, we performed X-ray transient absorption (XTA) spectroscopy at the Fe and Co K edges. The Fe K-edge XTA spectrum at 150 ps shows a red shift of the absorption edge that is consistent with an Fe(II) high-spin state, as supported by ab initio calculations. The transient signal detected at the Co K-edge is 50× weaker, confirming the ferrocene-centered character of the excited state. Fitting of the transient extended X-ray absorption fine structure region yields an Fe-C bond length increase of 0.25 ± 0.1 Å in the excited state, as expected for the high-spin state based on DFT. Altogether, these results demonstrate that the high-spin state of ferrocene should be considered when designing donor-acceptor assemblies for photocatalysis and photovoltaics.
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U2 - 10.1021/jacs.4c05646
DO - 10.1021/jacs.4c05646
M3 - Article
C2 - 39051542
AN - SCOPUS:85199722815
SN - 0002-7863
VL - 146
SP - 21651
EP - 21663
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 31
ER -