Metal-to-Ligand Charge-Transfer Emissions of Ruthenium(II) Pentaammine Complexes with Monodentate Aromatic Acceptor Ligands and Distortion Patterns of their Lowest Energy Triplet Excited States

2015 ◽  
Vol 54 (17) ◽  
pp. 8495-8508 ◽  
Author(s):  
Chia Nung Tsai ◽  
Shivnath Mazumder ◽  
Xiu Zhu Zhang ◽  
H. Bernhard Schlegel ◽  
Yuan Jang Chen ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Excited States ◽  
Ligand Charge Transfer ◽  
Triplet Excited States

scholarly journals The Effect of N-Heterocyclic Carbene Units on the Absorption Spectra of Fe(II) Complexes: A Challenge for Theory

2020 ◽  
Author(s):  
Olga S. Bokareva ◽  
Omar Baig ◽  
Mohamed Al-Marri ◽  
Oliver Kühn ◽  
Leticia Gonzalez
Keyword(s):  
Charge Transfer ◽  
Absorption Spectra ◽  
Excited States ◽  
Partial Charge Transfer ◽  
Polypyridyl Ligands ◽  
Electronic Excited States ◽  
Heteroleptic Complexes ◽  
Ligand Charge Transfer ◽  
Exact Exchange ◽  
Triplet Excited States

<div>The absorption spectra of five Fe(II) homoleptic and heteroleptic complexes containing strong sigma-donating N-heterocyclic carbene (NHC) and polypyridyl ligands have been theoretically characterized using a tuned range-separation functional.</div><div>From a benchmark comparison of the obtained results against other functionals and a multiconfigurational reference, it is concluded that none of the methods is completely satisfactory to describe the absorption spectra.</div><div>Using a compromised choice of 20\% exact exchange, the electronic excited states underlying the absorption spectra are analyzed.</div><div>The low-lying energy band of all the compounds shows predominant metal-to-ligand charge transfer (MLCT) character while the triplet excited states have metal-centered (MC) nature, which becomes more pronounced with increasing the number of NHC-donor groups. Excited MC states with partial charge transfer to the NHC-donor groups are higher in energy than comparable states without these contributions. The presence of the low-lying MC states prevents the formation of long-lived MLCT states.</div>

scholarly journals The Effect of N-Heterocyclic Carbene Units on the Absorption Spectra of Fe(II) Complexes: A Challenge for Theory

2020 ◽  
Author(s):  
Olga S. Bokareva ◽  
Omar Baig ◽  
Mohamed Al-Marri ◽  
Oliver Kühn ◽  
Leticia Gonzalez
Keyword(s):  
Charge Transfer ◽  
Absorption Spectra ◽  
Excited States ◽  
Partial Charge Transfer ◽  
Polypyridyl Ligands ◽  
Electronic Excited States ◽  
Heteroleptic Complexes ◽  
Ligand Charge Transfer ◽  
Exact Exchange ◽  
Triplet Excited States

<div>The absorption spectra of five Fe(II) homoleptic and heteroleptic complexes containing strong sigma-donating N-heterocyclic carbene (NHC) and polypyridyl ligands have been theoretically characterized using a tuned range-separation functional.</div><div>From a benchmark comparison of the obtained results against other functionals and a multiconfigurational reference, it is concluded that none of the methods is completely satisfactory to describe the absorption spectra.</div><div>Using a compromised choice of 20\% exact exchange, the electronic excited states underlying the absorption spectra are analyzed.</div><div>The low-lying energy band of all the compounds shows predominant metal-to-ligand charge transfer (MLCT) character while the triplet excited states have metal-centered (MC) nature, which becomes more pronounced with increasing the number of NHC-donor groups. Excited MC states with partial charge transfer to the NHC-donor groups are higher in energy than comparable states without these contributions. The presence of the low-lying MC states prevents the formation of long-lived MLCT states.</div>

Synthesis and Photochemical Properties of Re(I) Tricarbonyl Complexes Bound to Thione and Thiazole-2-ylidene Ligands

2020 ◽  
Author(s):  
Matthew Stout ◽  
Brian Skelton ◽  
Alexandre N. Sobolev ◽  
Paolo Raiteri ◽  
Massimiliano Massi ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Excited States ◽  
Ligand Exchange ◽  
Ligand Substitution ◽  
Bidentate Ligand ◽  
The Other ◽  
Ligand Exchange Reaction ◽  
Multiple Products ◽  
Ligand Charge Transfer ◽  
Photochemical Properties

<p>Three Re(I) tricarbonyl complexes, with general formulation Re(N^L)(CO)<sub>3</sub>X (where N^L is a bidentate ligand containing a pyridine functionalized in the position 2 with a thione or a thiazol-2-ylidene group and X is either chloro or bromo) were synthesized and their reactivity explored in terms of solvent-dependent ligand substitution, both in the ground and excited states. When dissolved in acetonitrile, the complexes bound to the thione ligand underwent ligand exchange with the solvent resulting in the formation of Re(NCMe)<sub>2</sub>(CO)<sub>3</sub>X. The exchange was found to be reversible, and the starting complex was reformed upon removal of the solvent. On the other hand, the complexes appeared inert in dichloromethane or acetone. Conversely, the complex bound to the thiazole-2-ylidene ligand did not display any ligand exchange reaction in the dark, but underwent photoactivated ligand substitution when excited to its lowest metal-to-ligand charge transfer manifold. Photolysis of this complex in acetonitrile generated multiple products, including Re(I) tricarbonyl and dicarbonyl solvato-complexes as well as free thiazole-2-ylidene ligand.</p>

scholarly journals Rational Design of TADF Polymers Using a Donor-Acceptor Monomer with Enhanced TADF Efficiency Induced by the Energy Alignment of Charge Transfer and Local Triplet Excited States

2016 ◽  
Vol 4 (4) ◽  
pp. 597-607 ◽  
Author(s):  
Roberto S. Nobuyasu ◽  
Zhongjie Ren ◽  
Gareth C. Griffiths ◽  
Andrei S. Batsanov ◽  
Przemyslaw Data ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Excited States ◽  
Rational Design ◽  
Donor Acceptor ◽  
Triplet Excited States

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.

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