Direct evidence for rearrangement of five-coordinate excited-state fragments generated from ligand field photodissociation in d6 complexes of rhodium(III)

1981 ◽  
Vol 20 (1) ◽  
pp. 280-281 ◽  
Author(s):  
Stephen F. Clark ◽  
John D. Petersen
Keyword(s):  
Excited State ◽  
Direct Evidence ◽  
Ligand Field

scholarly journals Using Ultrafast X-ray Spectroscopy To Address Questions in Ligand-Field Theory: The Excited State Spin and Structure of [Fe(dcpp)2]2+

2019 ◽  
Vol 58 (14) ◽  
pp. 9341-9350 ◽  
Author(s):  
Alexander Britz ◽  
Wojciech Gawelda ◽  
Tadesse A. Assefa ◽  
Lindsey L. Jamula ◽  
Jonathan T. Yarranton ◽  
...  
Keyword(s):  
Field Theory ◽  
Excited State ◽  
Ligand Field ◽  
Ligand Field Theory ◽  
X Ray ◽  
State Spin

scholarly journals Outer-sphere effects on ligand-field excited-state dynamics: solvent dependence of high-spin to low-spin conversion in [Fe(bpy)3]2+

2020 ◽  
Vol 11 (20) ◽  
pp. 5191-5204 ◽  
Author(s):  
Jennifer N. Miller ◽  
James K. McCusker
Keyword(s):  
Excited State ◽  
Reorganization Energy ◽  
Outer Sphere ◽  
Ligand Field ◽  
Spin Conversion ◽  
Energy Effect ◽  
Time Resolved ◽  
Excited State Dynamics ◽  
State Recovery ◽  
Solvent Dependence

Time-resolved spectroscopic measurements of ground-state recovery for [Fe(bpy)3]2+ reveal that the solvent can induce an outer-sphere reorganization energy effect on excited-state dynamics involving metal-centered ligand-field electronic states.

scholarly journals Multireference Description of Nickel–Aryl Homolytic Bond Dissociation Processes in Photoredox Catalysis

2020 ◽  
Author(s):  
David Cagan ◽  
Gautam Stroscio ◽  
Alexander Cusumano ◽  
Ryan Hadt
Keyword(s):  
Electronic Structure ◽  
Excited State ◽  
Charge Transfer ◽  
Density Functional ◽  
Single Photon ◽  
Ligand Field ◽  
Initial Population ◽  
Bond Dissociation ◽  
Ligand Charge Transfer ◽  
Triplet Excited States

<p>Multireference electronic structure calculations consistent with known experimental data have elucidated a novel mechanism for photo-triggered Ni(II)–C homolytic bond dissociation in Ni 2,2’-bipyridine (bpy) photoredox catalysts. Previously, a thermally assisted dissociation from the lowest energy triplet ligand field excited state was proposed and supported by density functional theory (DFT) calculations that reveal a barrier of ~30 kcal mol<sup>-1</sup>. In contrast, multireference ab initio calculations suggest this process is disfavored, with barrier heights of ~70 kcal mol<sup>-1</sup>, and highlight important ligand noninnocent contributions to excited state relaxation and bond dissociation processes that are not captured with DFT. In the multireference description, photo-triggered Ni(II)–C homolytic bond dissociation occurs via initial population of a singlet Ni(II)-to-bpy metal-to-ligand charge transfer (<sup>1</sup>MLCT) excited state followed by intersystem crossing and aryl-to-Ni(III) charge transfer, overall a formal two-electron transfer process driven by a single photon. This results in repulsive triplet excited states from which spontaneous homolytic bond dissociation can occur, effectively competing with relaxation to the lowest energy, nondissociative triplet Ni(II) ligand field excited state. These findings guide important electronic structure considerations for the experimental and computational elucidation of the mechanisms of ground and excited state cross-coupling catalysis mediated by Ni heteroaromatic complexes.</p>

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>

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