scholarly journals Controlling the Lifetime of the Triplet MLCT State in Fe(II) Polypyridyl Complexes through Ligand Modification

Inorganics ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 16 ◽  
Author(s):  
Jianfang Wu ◽  
Marc Alías ◽  
Coen de Graaf
Keyword(s):  
Charge Transfer ◽  
Field Strength ◽  
Computational Study ◽  
Relative Energy ◽  
Ligand Field ◽  
Polypyridyl Complexes ◽  
Ligand Modification ◽  
Ligand Charge Transfer ◽  
Mlct State

A computational study is presented in which two strategies of ligand modifications have been explored to invert the relative energy of the metal-to-ligand charge transfer (MLCT) and metal-centered (MC) state in Fe(II)-polypyridyl complexes. Replacing the bipyridines by stronger σ donors increases the ligand-field strength and pushes the MC state to higher energy, while the use of ligands with a larger π conjugation leads to lower MLCT energies.

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>

Isolation of a metal-to-ligand charge-transfer (MLCT) state of a tris 1,4-diimine complex of iron in the solid state: X-ray crystal structure and EPR

2017 ◽  
Vol 41 (2) ◽  
pp. 452-456 ◽  
Author(s):  
Nirmal K. Shee ◽  
Michael G. B. Drew ◽  
Dipankar Datta
Keyword(s):  
Crystal Structure ◽  
Charge Transfer ◽  
Solid State ◽  
X Ray ◽  
Ligand Charge Transfer ◽  
Mlct State

Using 5,6-dihydro-5,6-epoxy-1,10-phenanthroline as the ligand L, the X-ray crystal structure of [FeL3](ClO4)2·2H2O is determined.

Luminescence of a New Ru(II) Polypyridine Complex Controlled by a Redox-Responsive Protonable Anthra[1,10]phenanthrolinequinone

2005 ◽  
Vol 70 (11) ◽  
pp. 1891-1908 ◽  
Author(s):  
František Hartl ◽  
Sandrine Vernier ◽  
Peter Belser
Keyword(s):  
Charge Transfer ◽  
Quantum Yield ◽  
Emission Intensity ◽  
Luminescence Quenching ◽  
Luminescence Quantum Yield ◽  
Ligand Charge Transfer ◽  
Redox Responsive ◽  
Electron Reduction ◽  
Mlct State

Redox-controlled luminescence quenching is presented for a new Ru(II)-bipyridine complex [Ru(bpy)2(1)]2+ where ligand 1 is an anthra[1,10]phenanthrolinequinone. The complex emits from a short-lived metal-to-ligand charge transfer, 3MLCT state (τ = 5.5 ns in deaerated acetonitrile) with a low luminescence quantum yield (5 × 10-4). The emission intensity becomes significantly enhanced when the switchable anthraquinone unit is reduced to corresponding hydroquinone. On the contrary, chemical one-electron reduction of the anthraquinone moiety to semiquinone in aprotic tetrahydrofuran results in total quenching of the emission.

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>

Tuning of the lowest excited states in mixed ruthenium(ii) polypyridyl complexes having RuN6 cores by the conformation of the ancillary ligand. Emission from a 3ligand-to-ligand-charge-transfer state

2016 ◽  
Vol 40 (6) ◽  
pp. 5002-5009 ◽  
Author(s):  
Nirmal K. Shee ◽  
Michael G. B. Drew ◽  
Dipankar Datta
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Excited States ◽  
Small Difference ◽  
Charge Transfer State ◽  
Ancillary Ligand ◽  
Polypyridyl Complexes ◽  
Ligand Charge Transfer ◽  
Transfer State

A small difference in the conformation of an ancillary ligand L determines the lowest excited state in [Ru(bpy)2L]2+ and [Ru(phen)2L]2+.

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