RuII(α-diimine) or RuIII(α-diimine·-)? Structural, Spectroscopic, and Theoretical Evidence for the Stabilization of a Prominent Metal-to-Ligand Charge-Transfer Excited-State Configuration in the Ground State

2013 ◽  
Vol 2014 (1) ◽  
pp. 110-119 ◽  
Author(s):  
Anita Grupp ◽  
Martina Bubrin ◽  
Fabian Ehret ◽  
Qiang Zeng ◽  
František Hartl ◽  
...  
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Ground State ◽  
Ligand Charge Transfer ◽  
Theoretical Evidence ◽  
State Configuration

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.

Organometallic ferromagnets

1990 ◽  
Vol 330 (1610) ◽  
pp. 205-215 ◽  
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Ground State ◽  
Magnetic Coupling ◽  
Organometallic Complexes ◽  
Electron Configuration ◽  
Ferromagnetic Coupling ◽  
New Materials ◽  
Linear Chains ◽  
Configuration Mixing

Some organometallic solids comprising linear chains of alternating m 8 = 1/2 metallocenium donors, D, and cyanocarbon acceptors, A, i.e. ••• D +*A~*D+*A- * •••, exhibit cooperative magnetic phenomena, i.e. ferro-, antiferro-, ferri-, and meta-magnetism. For [Fe II (C 5 Me 5 ) 2 ]+*[T C N E ]- (Me = methyl; T C N E = tetracyanoethylene) bulk ferromagnetic behaviour is observed below the Curie temperature of 4.8 K. Replacement of Fe III with Fe II , Ni III and Cr III leads to complexes with dia-, antiferro- and ferrimagnetic behaviour, respectively. These results are consistent with a model of configuration mixing of the lowest charge transfer excited state with the ground state developed earlier to understand the magnetic coupling of such systems. The model predicts the magnetic coupling as a function of electron configuration and direction of charge transfer (retro or reverse) and is a useful guide to designing new organic and /or organometallic complexes with cooperative magnetic coupling. To test the model and identify new materials with ferromagnetic coupling new TCNE-based electron transfer salts were prepared.

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.

scholarly journals Role of active site conformational changes in photocycle activation of the AppA BLUF photoreceptor

2017 ◽  
Vol 114 (7) ◽  
pp. 1480-1485 ◽  
Author(s):  
Puja Goyal ◽  
Sharon Hammes-Schiffer
Keyword(s):  
Electron Transfer ◽  
Free Energy ◽  
Excited State ◽  
Charge Transfer ◽  
Conformational Changes ◽  
Ground State ◽  
Active Site ◽  
Locally Excited ◽  
Proton Relay ◽  
Locally Excited State

Blue light using flavin adenine dinucleotide (BLUF) proteins are essential for the light regulation of a variety of physiologically important processes and serve as a prototype for photoinduced proton-coupled electron transfer (PCET). Free-energy simulations elucidate the active site conformations in the AppA (activation of photopigment and puc expression) BLUF domain before and following photoexcitation. The free-energy profile for interconversion between conformations with either Trp104 or Met106 closer to the flavin, denoted Trpin/Metout and Trpout/Metin, reveals that both conformations are sampled on the ground state, with the former thermodynamically favorable by ∼3 kcal/mol. These results are consistent with the experimental observation of both conformations. To analyze the proton relay from Tyr21 to the flavin via Gln63, the free-energy profiles for Gln63 rotation were calculated on the ground state, the locally excited state of the flavin, and the charge-transfer state associated with electron transfer from Tyr21 to the flavin. For the Trpin/Metout conformation, the hydrogen-bonding pattern conducive to the proton relay is not thermodynamically favorable on the ground state but becomes more favorable, corresponding to approximately half of the configurations sampled, on the locally excited state. The calculated energy gaps between the locally excited and charge-transfer states suggest that electron transfer from Tyr21 to the flavin is more facile for configurations conducive to proton transfer. When the active site conformation is not conducive to PCET from Tyr21, Trp104 can directly compete with Tyr21 for electron transfer to the flavin through a nonproductive pathway, impeding the signaling efficiency.

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