scholarly journals Competition Between Intersystem Crossing and Vibrational Cooling in Photoinduced Valence Tautomerism of a Cobalt-Dioxolene Complex Revealed with Femtosecond M-Edge XANES

2019 ◽  
Author(s):  
Ryan Ash ◽  
Kaili Zhang ◽  
Josh Vura-Weis
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
High Spin ◽  
Ground State ◽  
Extreme Ultraviolet ◽  
High Harmonic ◽  
Ligand Field ◽  
Intersystem Crossing ◽  
Valence Tautomerism ◽  
Vibrational Cooling

Cobalt complexes that undergo charge-transfer induced spin-transitions (CTIST) or valence tautomerism (VT) from low spin (LS) Co(III) to high spin (HS) Co(II) are potential candidates for magneto-optical switches. We use M-edge XANES spectroscopy with 40 fs time resolution to measure the excited-state dynamics of Co(III)(Cat-N-SQ)(Cat-N-BQ), where Cat-N-BQ and Cat-N-SQ are the singly and doubly reduced forms of the 2-(2-hydroxy-3,5-di-tert-butylphenyl-imino)-4,6-di-tert-butylcyclohexa-3,5-dienone ligand. The extreme ultraviolet probe pulses, produced using a tabletop high-harmonic generation light source, measure 3p3d transitions and are sensitive to the spin and oxidation state of the Co center. Photoexcitation at 525 nm produces a low-spin Co(II) ligand-to-metal charge transfer state which undergoes intersystem crossing to high-spin Co(II) in 67 fs. Vibrational cooling from this hot HS Co(II) state competes on the hundreds-of-fs timescale with back-intersystem crossing to the ground state, with 60% of the population trapped in a cold HS Co(II) state for 24 ps. Ligand field multiplet simulations accurately reproduce the ground-state spectra and support the excited-state assignments. This work demonstrates the ability of M-edge XANES to measure ultrafast photophysics of molecular Co complexes.<br><br><br>

scholarly journals Photoinduced Valence Tautomerism of a Cobalt-Dioxolene Complex Revealed with Femtosecond M-Edge XANES

2019 ◽  
Author(s):  
Ryan Ash ◽  
Kaili Zhang ◽  
Josh Vura-Weis
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
High Spin ◽  
Ground State ◽  
Extreme Ultraviolet ◽  
High Harmonic ◽  
Ligand Field ◽  
Intersystem Crossing ◽  
Valence Tautomerism ◽  
Reduced Forms

Cobalt complexes that undergo charge-transfer induced spin-transitions (CTIST) or valence tautomerism (VT) from low spin (LS) Co(III) to high spin (HS) Co(II) are potential candidates for magneto-optical switches. We use M-edge XANES spectroscopy with 40 fs time resolution to measure the excited-state dynamics of Co(III)(Cat-N-SQ)(Cat-N-BQ), where Cat-N-BQ and Cat-N-SQ are the singly and doubly reduced forms of the 2-(2-hydroxy-3,5-di-tert-butylphenyl-imino)-4,6-di-tert-butylcyclohexa-3,5-dienone ligand. The extreme ultraviolet probe pulses, produced using a tabletop high-harmonic generation light source, measure 3p3d transitions and are sensitive to the spin and oxidation state of the Co center. Photoexcitation at 525 nm produces a low-spin Co(II) ligand-to-metal charge transfer state which undergoes intersystem crossing to high-spin Co(II) in 67 fs. Vibrational cooling from this hot HS Co(II) state competes on the hundreds-of-fs timescale with back-intersystem crossing to the ground state, with 60% of the population trapped in a cold HS Co(II) state for 24 ps. Ligand field multiplet simulations accurately reproduce the ground-state spectra and support the excited-state assignments. This work demonstrates the ability of M-edge XANES to measure ultrafast photophysics of molecular Co complexes.<br><br><br>

Photoinduced Valence Tautomerism of a Cobalt-Dioxolene Complex Revealed with Femtosecond M-Edge XANES

2019 ◽  
Author(s):  
Ryan Ash ◽  
Kaili Zhang ◽  
Josh Vura-Weis
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
High Spin ◽  
Ground State ◽  
Extreme Ultraviolet ◽  
High Harmonic ◽  
Ligand Field ◽  
Intersystem Crossing ◽  
Valence Tautomerism ◽  
Reduced Forms

Cobalt complexes that undergo charge-transfer induced spin-transitions (CTIST) or valence tautomerism (VT) from low spin (LS) Co(III) to high spin (HS) Co(II) are potential candidates for magneto-optical switches. We use M-edge XANES spectroscopy with 40 fs time resolution to measure the excited-state dynamics of Co(III)(Cat-N-SQ)(Cat-N-BQ), where Cat-N-BQ and Cat-N-SQ are the singly and doubly reduced forms of the 2-(2-hydroxy-3,5-di-tert-butylphenyl-imino)-4,6-di-tert-butylcyclohexa-3,5-dienone ligand. The extreme ultraviolet probe pulses, produced using a tabletop high-harmonic generation light source, measure 3p3d transitions and are sensitive to the spin and oxidation state of the Co center. Photoexcitation at 525 nm produces a low-spin Co(II) ligand-to-metal charge transfer state which undergoes intersystem crossing to high-spin Co(II) in 67 fs. Vibrational cooling from this hot HS Co(II) state competes on the hundreds-of-fs timescale with back-intersystem crossing to the ground state, with 60% of the population trapped in a cold HS Co(II) state for 24 ps. Ligand field multiplet simulations accurately reproduce the ground-state spectra and support the excited-state assignments. This work demonstrates the ability of M-edge XANES to measure ultrafast photophysics of molecular Co complexes.<br><br><br>

Sub-100 Fs Intersystem Crossing to a Metal-Centered Triplet in Ni(II)OEP Observed with M-Edge XANES

2019 ◽  
Author(s):  
Elizabeth S. Ryland ◽  
Kaili Zhang ◽  
Josh Vura-Weis
Keyword(s):  
Excited State ◽  
Time Resolution ◽  
Transient Absorption ◽  
Extreme Ultraviolet ◽  
High Harmonic ◽  
Transient Absorption Spectroscopy ◽  
Intersystem Crossing ◽  
Edge Structure ◽  
State Spin ◽  
X Ray Absorption

Nickel porphyrins have been extenstively studied as photosensitizers due to their long-lived metal-centered excited states. The multiplicity of the (d,d) state, and/or the rate of intersystem crossing between singlet and triplet metal-centered states, has remained uncertain due to the spin-insensitivity of many spectral probes. In this work, we directly probe the metal 3d shell occupation of nickel(II) octaethylporphyrin (NiOEP) using femtosecond M2,3-edge X-ray absorption near-edge structure (XANES). A tabletop high-harmonic source is used to perform 400 nm pump, extreme-ultraviolet probe transient absorption spectroscopy with ~100 fs time resolution. Photoexcitation produces a (π,π*) state that evolves with a time constant of 48 fs to a vibrationally hot metal-centered triplet 3(d,d) excited state with a lifetime of 595 ps. The spin sensitivity of M-edge XANES allows the 3(d,d) state to be distinguished from a potential 1(d,d) state, as shown by charge transfer multiplet simulations and comparison to triplet nickel(II) oxide. Vibrational cooling of the hot triplet state occurs over tens of ps, with minimal change in the electronic structure of the nickel(II) center. No evidence of an LMCT or MLCT intermediate state is seen within the time resolution of the instrument, suggesting that if such a state exists in NiOEP it depopulates in <25 fs. Finally, this study demonstrates the ability of table high-harmonic XUV sources to measure excited-state spin transitions in molecular transition metal complexes.

scholarly journals Ballistic ΔS=2 Intersystem Crossing in a Cobalt Cubane Following Ligand-Field Excitation Probed by Extreme Ultraviolet Spectroscopy

2021 ◽  
Author(s):  
Yusef Shari'ati ◽  
Josh Vura-Weis
Keyword(s):  
Excited State ◽  
Extreme Ultraviolet ◽  
Xanes Spectroscopy ◽  
Ligand Field ◽  
Ultraviolet Spectroscopy ◽  
Intersystem Crossing ◽  
Edge Structure ◽  
X Ray ◽  
Field Excitation ◽  
X Ray Absorption

Femtosecond M2,3-edge X-ray absorption near-edge structure (XANES) spectroscopy is used to probe the excited-state dynamics of the cobalt cubane [CoIII4O4](OAc)4(py)4 (OAc = acetate, py = pyridine), a model for water...

scholarly journals Ballistic ΔS=2 Intersystem Crossing in a Cobalt Cubane Following Ligand-Field Excitation Probed by Extreme Ultraviolet Spectroscopy

2021 ◽  
Author(s):  
Yusef Shari'ati ◽  
Josh Vura-Weis
Keyword(s):  
Excited State ◽  
Water Oxidation ◽  
Extreme Ultraviolet ◽  
Ligand Field ◽  
Ultraviolet Spectroscopy ◽  
Intersystem Crossing ◽  
Edge Structure ◽  
X Ray ◽  
Field Excitation ◽  
X Ray Absorption

Femtosecond M2,3-edge X-ray absorption near-edge structure (XANES) spectroscopy is used to probe the excited-state dynamics of the cobalt cubane [CoIII4O4](OAc)4(py)4 (OAc = acetate, py = pyridine), a model for water oxidation catalysts. After ligand-field excitation, intersystem crossing to a metal-centered quintet occurs in 38 fs. 30% of the hot quintet undergoes ballistic back-ISC directly to the singlet ground stat, with the remainder relaxing to a long-lived triplet.

Sub-100 Fs Intersystem Crossing to a Metal-Centered Triplet in Ni(II)OEP Observed with M-Edge XANES

2019 ◽  
Author(s):  
Elizabeth S. Ryland ◽  
Kaili Zhang ◽  
Josh Vura-Weis
Keyword(s):  
Excited State ◽  
Time Resolution ◽  
Transient Absorption ◽  
Extreme Ultraviolet ◽  
High Harmonic ◽  
Transient Absorption Spectroscopy ◽  
Intersystem Crossing ◽  
Edge Structure ◽  
State Spin ◽  
X Ray Absorption

Nickel porphyrins have been extenstively studied as photosensitizers due to their long-lived metal-centered excited states. The multiplicity of the (d,d) state, and/or the rate of intersystem crossing between singlet and triplet metal-centered states, has remained uncertain due to the spin-insensitivity of many spectral probes. In this work, we directly probe the metal 3d shell occupation of nickel(II) octaethylporphyrin (NiOEP) using femtosecond M2,3-edge X-ray absorption near-edge structure (XANES). A tabletop high-harmonic source is used to perform 400 nm pump, extreme-ultraviolet probe transient absorption spectroscopy with ~100 fs time resolution. Photoexcitation produces a (π,π*) state that evolves with a time constant of 48 fs to a vibrationally hot metal-centered triplet 3(d,d) excited state with a lifetime of 595 ps. The spin sensitivity of M-edge XANES allows the 3(d,d) state to be distinguished from a potential 1(d,d) state, as shown by charge transfer multiplet simulations and comparison to triplet nickel(II) oxide. Vibrational cooling of the hot triplet state occurs over tens of ps, with minimal change in the electronic structure of the nickel(II) center. No evidence of an LMCT or MLCT intermediate state is seen within the time resolution of the instrument, suggesting that if such a state exists in NiOEP it depopulates in <25 fs. Finally, this study demonstrates the ability of table high-harmonic XUV sources to measure excited-state spin transitions in molecular transition metal complexes.

Spin-Forbidden Excitation Enables Infrared Photoredox Catalysis

2020 ◽  
Author(s):  
Tomislav Rovis ◽  
Benjamin D. Ravetz ◽  
Nicholas E. S. Tay ◽  
Candice Joe ◽  
Melda Sezen-Edmonds ◽  
...  
Keyword(s):  
Excited State ◽  
Ground State ◽  
Intersystem Crossing ◽  
Photoredox Catalysis ◽  
Infrared Irradiation ◽  
Triplet Excitation ◽  
New Family ◽  
Ir Light

We describe a new family of catalysts that undergo direct ground state singlet to excited state triplet excitation with IR light, leading to photoredox catalysis without the energy waste associated with intersystem crossing. The finding allows a mole scale reaction in batch using infrared irradiation.

Electroabsorption spectra of push–pull porphyrins in solution and in solid films

2015 ◽  
Vol 19 (01-03) ◽  
pp. 527-534
Author(s):  
Kamlesh Awasthi ◽  
Hung-Yu Hsu ◽  
Hung-Chu Chiang ◽  
Chi-Lun Mai ◽  
Chen-Yu Yeh ◽  
...  
Keyword(s):  
Dipole Moment ◽  
Excited State ◽  
Charge Transfer ◽  
Electric Dipole Moment ◽  
Electric Dipole ◽  
Ground State ◽  
Benzene Solution ◽  
Solid Films ◽  
The One ◽  
Interfacial Charge

Polarized electroabsorption (E-A) spectra of highly efficient porphyrin sensitizers (YD2 and YD2-oC8) have been measured in benzene solution. Polarized E-A spectra of these push–pull porphyrins embedded in poly(methyl methacrylate) films or sensitized on TiO 2 films are also observed. Based on the analysis of the E-A spectra, the magnitude of the electric dipole moment both in the ground state and in the lowest excited state have been evaluated in solution and in solid films. The electric dipole moment in the excited state of these compounds is very large on TiO 2 films, suggesting the interfacial charge transfer on TiO 2 surface following photoexcitation of porphyrin dyes. The electric dipole moment in the excited state evaluated from the E-A spectra is very different from the one evaluated from the electrophotoluminescence spectra on TiO 2, suggesting that the strong local field of TiO 2 films is applied to the fluorescing dyes attached to TiO 2 films.

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