Electroabsorption Studies of Metal-to-Ligand Charge Transfer in Ru(phenanthroline)32+:  Evidence for Intrinsic Charge Localization in the Initially Formed Excited State

1997 ◽  
Vol 36 (15) ◽  
pp. 3318-3321 ◽  
Author(s):  
Laba Karki ◽  
Joseph T. Hupp
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Charge Localization ◽  
Ligand Charge Transfer

A density functional theory and spectroscopic study of intramolecular quenching of metal-to-ligand charge-transfer excited states in some mono-bipyridine ruthenium(II) complexes

2014 ◽  
Vol 92 (10) ◽  
pp. 996-1009 ◽  
Author(s):  
Shivnath Mazumder ◽  
Ryan A. Thomas ◽  
Richard L. Lord ◽  
H. Bernhard Schlegel ◽  
John F. Endicott
Keyword(s):  
Density Functional Theory ◽  
Excited State ◽  
Charge Transfer ◽  
Excited States ◽  
Lower Energy ◽  
Density Functional ◽  
Dimethyl Sulfide ◽  
Intramolecular Electron Transfer ◽  
Functional Theory ◽  
Ligand Charge Transfer

The complexes [Ru(NCCH3)4bpy]2+ and [Ru([14]aneS4)bpy]2+ ([14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane, bpy = 2,2′-bipyridine) have similar absorption and emission spectra but the 77 K metal-to-ligand charge-transfer (MLCT) excited state emission lifetime of the latter is less than 0.3% that of the former. Density functional theory modeling of the lowest energy triplet excited states indicates that triplet metal centered (3MC) excited states are about 3500 cm−1 lower in energy than their 3MLCT excited states in both complexes. The differences in excited state lifetimes arise from a much larger coordination sphere distortion for [Ru(NCCH3)4bpy]2+ and the associated larger reorganizational barrier for intramolecular electron transfer. The smaller ruthenium ligand distortions of the [Ru([14]aneS4)bpy]2+ complex are apparently a consequence of stereochemical constraints imposed by the macrocyclic [14]aneS4 ligand, and the 3MC excited state calculated for the unconstrained [Ru(S(CH3)2)4bpy]2+ complex (S(CH3)2 = dimethyl sulfide) is distorted in a manner similar to that of [Ru(NCCH3)4bpy]2+. Despite the lower energy calculated for its 3MC than 3MLCT excited state, [Ru(NCCH3)4bpy]2+ emits strongly in 77 K glasses with an emission quantum yield of 0.47. The emission is biphasic with about a 1 μs lifetime for its dominant (86%) emission component. The 405 nm excitation used in these studies results in a significant amount of photodecomposition in the 77 K glasses. This is a temperature-dependent biphotonic process that most likely involves the bipyridine-radical anionic moiety of the 3MLCT excited state. A smaller than expected value found for the radiative rate constant is consistent with a lower energy 3MC than 3MLCT state.

Ultrafast excited state dynamics of [Cr(CO)4(bpy)]: revealing the relaxation between triplet charge-transfer states

RSC Advances ◽  
2016 ◽  
Vol 6 (25) ◽  
pp. 20507-20515 ◽  
Author(s):  
Fei Ma ◽  
Martin Jarenmark ◽  
Svante Hedström ◽  
Petter Persson ◽  
Ebbe Nordlander ◽  
...  
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Absorption Spectroscopy ◽  
Dft Calculation ◽  
Pump Probe ◽  
Excited State Dynamics ◽  
Mlct Transition ◽  
Ligand Charge Transfer ◽  
Probe Absorption

Ultrafast excited state dynamics of [Cr(CO)4(bpy)] upon metal-to-ligand charge-transfer (1MLCT) transition have been studied by pump-probe absorption spectroscopy and DFT calculation.

scholarly journals Sensitization of ultra-long-range excited-state electron transfer by energy transfer in a polymerized film

2012 ◽  
Vol 109 (38) ◽  
pp. 15132-15135 ◽  
Author(s):  
Akitaka Ito ◽  
David J. Stewart ◽  
Zhen Fang ◽  
M. Kyle Brennaman ◽  
Thomas J. Meyer
Keyword(s):  
Electron Transfer ◽  
Energy Transfer ◽  
Excited State ◽  
Charge Transfer ◽  
Long Range ◽  
Methyl Viologen ◽  
Polymer Network ◽  
Triplet Energy ◽  
Ligand Charge Transfer ◽  
Triplet Energy Transfer

Distance-dependent energy transfer occurs from the Metal-to-Ligand Charge Transfer (MLCT) excited state to an anthracene-acrylate derivative (Acr-An) incorporated into the polymer network of a semirigid poly(ethyleneglycol)dimethacrylate monolith. Following excitation, to Acr-An triplet energy transfer occurs followed by long-range, Acr-3An—Acr-An → Acr-An—Acr-3An, energy migration. With methyl viologen dication (MV2+) added as a trap, Acr-3An + MV2+ → Acr-An+ + MV+ electron transfer results in sensitized electron transfer quenching over a distance of approximately 90 Å.

Excited-state equilibration: a process leading to long-lived metal-to-ligand charge transfer luminescence in supramolecular systems

2005 ◽  
Vol 249 (13-14) ◽  
pp. 1336-1350 ◽  
Author(s):  
Nathan D. McClenaghan ◽  
Yoann Leydet ◽  
Béatrice Maubert ◽  
Maria Teresa Indelli ◽  
Sebastiano Campagna
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Supramolecular Systems ◽  
Ligand Charge Transfer

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>

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