1
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Zederkof DB, Møller KB, Nielsen MM, Haldrup K, González L, Mai S. Resolving Femtosecond Solvent Reorganization Dynamics in an Iron Complex by Nonadiabatic Dynamics Simulations. J Am Chem Soc 2022; 144:12861-12873. [PMID: 35776920 PMCID: PMC9305979 DOI: 10.1021/jacs.2c04505] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
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The ultrafast dynamical
response of solute–solvent interactions
plays a key role in transition metal complexes, where charge transfer
states are ubiquitous. Nonetheless, there exist very few excited-state
simulations of transition metal complexes in solution. Here, we carry
out a nonadiabatic dynamics study of the iron complex [Fe(CN)4(bpy)]2– (bpy = 2,2′-bipyridine)
in explicit aqueous solution. Implicit solvation models were found
inadequate for reproducing the strong solvatochromism in the absorption
spectra. Instead, direct solute–solvent interactions, in the
form of hydrogen bonds, are responsible for the large observed solvatochromic
shift and the general dynamical behavior of the complex in water.
The simulations reveal an overall intersystem crossing time scale
of 0.21 ± 0.01 ps and a strong reliance of this process
on nuclear motion. A charge transfer character analysis shows a branched
decay mechanism from the initially excited singlet metal-to-ligand
charge transfer (1MLCT) states to triplet states of 3MLCT and metal-centered (3MC) character. We also
find that solvent reorganization after excitation is ultrafast, on
the order of 50 fs around the cyanides and slower around the
bpy ligand. In contrast, the nuclear vibrational dynamics, in the
form of Fe–ligand bond changes, takes place on slightly longer
time scales. We demonstrate that the surprisingly fast solvent reorganizing
should be observable in time-resolved X-ray solution scattering experiments,
as simulated signals show strong contributions from the solute–solvent
scattering cross term. Altogether, the simulations paint a comprehensive
picture of the coupled and concurrent electronic, nuclear, and solvent
dynamics and interactions in the first hundreds of femtoseconds after
excitation.
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Affiliation(s)
- Diana Bregenholt Zederkof
- Department of Physics, Technical University of Denmark, Fysikvej, bygning 307, 2800 Kongens Lyngby, Denmark.,Scientific Instrument Femtosecond X-ray Experiments, European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Klaus B Møller
- Department of Chemistry, Technical University of Denmark, Kemitorvet, bygning 207, 2800 Kongens Lyngby, Denmark
| | - Martin M Nielsen
- Department of Physics, Technical University of Denmark, Fysikvej, bygning 307, 2800 Kongens Lyngby, Denmark
| | - Kristoffer Haldrup
- Department of Physics, Technical University of Denmark, Fysikvej, bygning 307, 2800 Kongens Lyngby, Denmark
| | - Leticia González
- Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna, Währinger Straße 17, 1090 Vienna, Austria
| | - Sebastian Mai
- Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna, Währinger Straße 17, 1090 Vienna, Austria
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2
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Larsen CB, Braun JD, Lozada IB, Kunnus K, Biasin E, Kolodziej C, Burda C, Cordones AA, Gaffney KJ, Herbert DE. Reduction of Electron Repulsion in Highly Covalent Fe-Amido Complexes Counteracts the Impact of a Weak Ligand Field on Excited-State Ordering. J Am Chem Soc 2021; 143:20645-20656. [PMID: 34851636 DOI: 10.1021/jacs.1c06429] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The ability to access panchromatic absorption and long-lived charge-transfer (CT) excited states is critical to the pursuit of abundant-metal molecular photosensitizers. Fe(II) complexes supported by benzannulated diarylamido ligands have been reported to broadly absorb visible light with nanosecond CT excited state lifetimes, but as amido donors exert a weak ligand field, this defies conventional photosensitizer design principles. Here, we report an aerobically stable Fe(II) complex of a phenanthridine/quinoline diarylamido ligand, Fe(ClL)2, with panchromatic absorption and a 3 ns excited-state lifetime. Using X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) at the Fe L-edge and N K-edge, we experimentally validate the strong Fe-Namido orbital mixing in Fe(ClL)2 responsible for the panchromatic absorption and demonstrate a previously unreported competition between ligand-field strength and metal-ligand (Fe-Namido) covalency that stabilizes the 3CT state over the lowest energy triplet metal-centered (3MC) state in the ground-state geometry. Single-crystal X-ray diffraction (XRD) and density functional theory (DFT) suggest that formation of this CT state depopulates an orbital with Fe-Namido antibonding character, causing metal-ligand bonds to contract and accentuating the geometric differences between CT and MC excited states. These effects diminish the driving force for electron transfer to metal-centered excited states and increase the intramolecular reorganization energy, critical properties for extending the lifetime of CT excited states. These findings highlight metal-ligand covalency as a novel design principle for elongating excited state lifetimes in abundant metal photosensitizers.
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Affiliation(s)
- Christopher B Larsen
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Jason D Braun
- Department of Chemistry and the Manitoba Institute for Materials, University of Manitoba, 144 Dysart Road, Winnipeg, MB R3T 2N2, Canada
| | - Issiah B Lozada
- Department of Chemistry and the Manitoba Institute for Materials, University of Manitoba, 144 Dysart Road, Winnipeg, MB R3T 2N2, Canada
| | - Kristjan Kunnus
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Elisa Biasin
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Charles Kolodziej
- Department of Chemistry, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States
| | - Clemens Burda
- Department of Chemistry, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States
| | - Amy A Cordones
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Kelly J Gaffney
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - David E Herbert
- Department of Chemistry and the Manitoba Institute for Materials, University of Manitoba, 144 Dysart Road, Winnipeg, MB R3T 2N2, Canada
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3
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Kožíšek J, Svoboda J, Zedník J, Vlčková B, Šloufová I. Resonance Raman Excitation Profiles of Fe(II)-Terpyridine Complexes: Electronic Effects of Ligand Modifications. J Phys Chem B 2021; 125:12847-12858. [PMID: 34758623 DOI: 10.1021/acs.jpcb.1c08366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Metal 2,2':6',2″-terpyridine (tpy) complexes are readily used as building blocks in metallo-supramolecular polymers that stand out for their photophysical properties in solar energy assemblies. Furthermore, Resonance Raman (RR) excitation profiles are sensitive indicators of the electronic properties of chromophores. Previously, using RR spectroscopy, we studied the [Fe(tpy)2]2+ complex and metallo-supramolecular polymers formed by tpy derivatives and Fe(II) ions. Here, we compare RR spectra of iron (Fe(II)) complexes with 4'-substituted tpy ligands─[Fe(4'-R-tpy)2]2+, with R = H (1a), Cl (2a), 4-chlorophenyl (3a), and 2-thienyl (4a) to describe changes in their electronic structure after functionalization. By combining theoretical calculations, RR, and UV/vis spectra, we elucidated differences in the RR excitation profiles of 1a, 2a, and 4a complexes. In all Raman modes, complexes 1a and 2a showed maximal enhancement only at 532 nm excitation, whereas complex 4a exhibited maximal enhancement selectively at either 532 or 633 nm excitations. Based on our calculations, the mixed metal/ligand character of the highest occupied molecular orbital (HOMO) of 4a complex manifests itself through selective enhancement of vibration modes, mainly localized on the 2-thienyl unit at 633 nm excitation, which may explain the unique behavior of this complex. Therefore, complex 4a is a prospective candidate for further detailed photophysical explorations toward developing sensitizers for solar cells.
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Affiliation(s)
- Jan Kožíšek
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 40 Prague 2, Czech Republic
| | - Jan Svoboda
- Institute of Macromolecular Chemistry, Czech Academy of Sciences, Heyrovskeho nam. 2, 162 06 Prague 6, Czech Republic
| | - Jiří Zedník
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 40 Prague 2, Czech Republic
| | - Blanka Vlčková
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 40 Prague 2, Czech Republic
| | - Ivana Šloufová
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 40 Prague 2, Czech Republic
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4
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Kwon HY, Ashley DC, Jakubikova E. Halogenation affects driving forces, reorganization energies and "rocking" motions in strained [Fe(tpy) 2] 2+ complexes. Dalton Trans 2021; 50:14566-14575. [PMID: 34586133 DOI: 10.1039/d1dt02314d] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Controlling the energetics of spin crossover (SCO) in Fe(II)-polypyridine complexes is critical for designing new multifunctional materials or tuning the excited-state lifetimes of iron-based photosensitizers. It is well established that the Fe-N "breathing" mode is important for intersystem crossing from the singlet to the quintet state, but this does not preclude other, less obvious, structural distortions from affecting SCO. Previous work has shown that halogenation at the 6 and 6'' positions of tpy (tpy = 2,2';6',2''-terpyridine) in [Fe(tpy)2]2+ dramatically increased the lifetime of the excited MLCT state and also had a large impact on the ground state spin-state energetics. To gain insight into the origins of these effects, we used density functional theory calculations to explore how halogenation impacts spin-state energetics and molecular structure in this system. Based on previous work we focused on the ligand "rocking" motion associated with SCO in [Fe(tpy)2]2+ by constructing one-dimensional potential energy surfaces (PESs) along the tpy rocking angle for various spin states. It was found that halogenation has a clear and predictable impact on ligand rocking and spin-state energetics. The rocking is correlated to numerous other geometrical distortions, all of which likely affect the reorganization energies for spin-state changes. We have quantified trends in reorganization energy and also driving force for various spin-state changes and used them to interpret the experimentally measured excited-state lifetimes.
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Affiliation(s)
- Hyuk-Yong Kwon
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Dr., Raleigh, NC 27695, USA.
| | - Daniel C Ashley
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Dr., Raleigh, NC 27695, USA.
| | - Elena Jakubikova
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Dr., Raleigh, NC 27695, USA.
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5
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Vittardi SB, Magar RT, Schrage BR, Ziegler CJ, Jakubikova E, Rack JJ. Evidence for a lowest energy 3MLCT excited state in [Fe(tpy)(CN) 3] . Chem Commun (Camb) 2021; 57:4658-4661. [PMID: 33977987 DOI: 10.1039/d1cc01090e] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Transient absorption data of [FeII(tpy)(CN)3]- reveals spectroscopic signatures indicative of 3MLCT with a ∼10 ps kinetic component. These data are supported by DFT and TD-DFT calculations, which show that excited state ordering is responsive to the number of cyanide ligands on the complex.
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Affiliation(s)
- Sebastian B Vittardi
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM 87131, USA.
| | - Rajani Thapa Magar
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM 87131, USA.
| | - Briana R Schrage
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | | | - Elena Jakubikova
- Knight Chemical Laboratory, Department of Chemistry, University of Akron, Akron, OH, USA.
| | - Jeffrey J Rack
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM 87131, USA.
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6
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Farcaş AA, Bende A. Theoretical modeling of the singlet-triplet spin transition in different Ni(II)-diketo-pyrphyrin-based metal-ligand octahedral complexes. Phys Chem Chem Phys 2021; 23:4784-4795. [PMID: 33599640 DOI: 10.1039/d0cp05366j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The structural stability, charge transfer effects and strength of the spin-orbit couplings in different Ni(ii)-ligand complexes have been studied at the DFT (B3LYP and CAM-B3LYP) and coupled cluster (DLPNO-CCSD(T)) levels of theory. Accordingly, two different, porphyrin- and diketo-pyrphyrin-based four-coordination macrocycles as planar ligands as well as pyridine (or pyrrole) and mesylate anion molecular groups as vertical ligands were considered in order to build metal-organic complexes with octahedral coordination configurations. For each molecular system, the identification of equilibrium geometries and the intersystem crossing (the minimum energy crossing) points between the potential energy surfaces of the singlet and triplet spin states is followed by computing the spin-orbit couplings between the two spin states. Structures, based on the diketo-pyrphyrin macrocycle as the planar ligand, show stronger six-coordination metal-organic complexes due to the extra electrostatic interaction between the positively charged central metal cation and the negatively charged vertical ligands. The results also show that the magnitude of the spin-orbit coupling is influenced by the atomic positions of deprotonations of the ligands, and implicitly the direction of the charge transfer between the ligand and the central metal ion.
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Affiliation(s)
- Alex-Adrian Farcaş
- Faculty of Physics, "Babeş-Bolyai" University, Mihail Kogalniceanu Street No. 1, Ro-400084 Cluj-Napoca, Romania
| | - Attila Bende
- Molecular and Biomolecular Physics Department, National Institute for Research and Development of Isotopic and Molecular Technologies, Donat Street, No. 67-103, Ro-400293 Cluj-Napoca, Romania.
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7
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Tran LN, Neuscamman E. Improving Excited-State Potential Energy Surfaces via Optimal Orbital Shapes. J Phys Chem A 2020; 124:8273-8279. [DOI: 10.1021/acs.jpca.0c07593] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Lan Nguyen Tran
- Department of Chemistry, University of California, Berkeley, California 94720, United States
- Ho Chi Minh City Institute of Physics, VAST, Ho Chi Minh City 700000, Vietnam
| | - Eric Neuscamman
- Department of Chemistry, University of California, Berkeley, California 94720, United States
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
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8
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Kunnus K, Li L, Titus CJ, Lee SJ, Reinhard ME, Koroidov S, Kjær KS, Hong K, Ledbetter K, Doriese WB, O'Neil GC, Swetz DS, Ullom JN, Li D, Irwin K, Nordlund D, Cordones AA, Gaffney KJ. Chemical control of competing electron transfer pathways in iron tetracyano-polypyridyl photosensitizers. Chem Sci 2020; 11:4360-4373. [PMID: 34122894 PMCID: PMC8159445 DOI: 10.1039/c9sc06272f] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Accepted: 04/15/2020] [Indexed: 12/15/2022] Open
Abstract
Photoinduced intramolecular electron transfer dynamics following metal-to-ligand charge-transfer (MLCT) excitation of [Fe(CN)4(2,2'-bipyridine)]2- (1), [Fe(CN)4(2,3-bis(2-pyridyl)pyrazine)]2- (2) and [Fe(CN)4(2,2'-bipyrimidine)]2- (3) were investigated in various solvents with static and time-resolved UV-Visible absorption spectroscopy and Fe 2p3d resonant inelastic X-ray scattering (RIXS). This series of polypyridyl ligands, combined with the strong solvatochromism of the complexes, enables the 1MLCT vertical energy to be varied from 1.64 eV to 2.64 eV and the 3MLCT lifetime to range from 180 fs to 67 ps. The 3MLCT lifetimes in 1 and 2 decrease exponentially as the MLCT energy increases, consistent with electron transfer to the lowest energy triplet metal-centred (3MC) excited state, as established by the Tanabe-Sugano analysis of the Fe 2p3d RIXS data. In contrast, the 3MLCT lifetime in 3 changes non-monotonically with MLCT energy, exhibiting a maximum. This qualitatively distinct behaviour results from a competing 3MLCT → ground state (GS) electron transfer pathway that exhibits energy gap law behaviour. The 3MLCT → GS pathway involves nuclear tunnelling for the high-frequency polypyridyl breathing mode (hν = 1530 cm-1), which is most displaced for complex 3, making this pathway significantly more efficient. Our study demonstrates that the excited state relaxation mechanism of Fe polypyridyl photosensitizers can be readily tuned by ligand and solvent environment. Furthermore, our study reveals that extending charge transfer lifetimes requires control of the relative energies of the 3MLCT and the 3MC states and suppression of the intramolecular distortion of the acceptor ligand in the 3MLCT excited state.
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Affiliation(s)
- Kristjan Kunnus
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University Menlo Park California 94025 USA
| | - Lin Li
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University Menlo Park California 94025 USA
| | - Charles J Titus
- Department of Physics, Stanford University Stanford California 94305 USA
| | - Sang Jun Lee
- SLAC National Accelerator Laboratory Menlo Park California 94025 USA
| | - Marco E Reinhard
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University Menlo Park California 94025 USA
| | - Sergey Koroidov
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University Menlo Park California 94025 USA
| | - Kasper S Kjær
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University Menlo Park California 94025 USA
| | - Kiryong Hong
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University Menlo Park California 94025 USA
| | - Kathryn Ledbetter
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University Menlo Park California 94025 USA
- Department of Physics, Stanford University Stanford California 94305 USA
| | | | - Galen C O'Neil
- National Institute of Standards and Technology Boulder CO 80305 USA
| | - Daniel S Swetz
- National Institute of Standards and Technology Boulder CO 80305 USA
| | - Joel N Ullom
- National Institute of Standards and Technology Boulder CO 80305 USA
| | - Dale Li
- SLAC National Accelerator Laboratory Menlo Park California 94025 USA
| | - Kent Irwin
- Department of Physics, Stanford University Stanford California 94305 USA
- SLAC National Accelerator Laboratory Menlo Park California 94025 USA
| | - Dennis Nordlund
- SLAC National Accelerator Laboratory Menlo Park California 94025 USA
| | - Amy A Cordones
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University Menlo Park California 94025 USA
| | - Kelly J Gaffney
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University Menlo Park California 94025 USA
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