On the role of ligand-field states for the photophysical properties of ruthenium(II) polypyridyl complexes

Sun, Qinchao; Mosquera-Vázquez, Sandra; Suffren, Yan; Hankache, Jihane; Amstutz, Nahid; Daku, Latévi Max Lawson; Vauthey, Eric; Hauser, Andreas

doi:10.1016/j.ccr.2014.07.004

Cited by 125 publications

(178 citation statements)

References 88 publications

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“…49 If the dissociative 3 MC state is the lowest-lying state on the triplet surface, the photochemical process is more likely to result in ligand dissociation. Figure 1 shows the relative energies of the optimized 3 MLCT and 3 MC geometries of the Ru(TQA) complex.…”

Section: Resultsmentioning

confidence: 99%

Selective Photodissociation of Acetonitrile Ligands in Ruthenium Polypyridyl Complexes Studied by Density Functional Theory

Mazumder

Endicott

et al. 2015

Inorg. Chem.

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Metal complexes that release ligands upon photoexcitation are important tools for biological research and show great potential as highly specific therapeutics. Upon excitation with visible light, [Ru(TQA)(MeCN)2]2+ [TQA = tris(2-quinolinylmethyl)amine] exchanges one of the two acetonitriles (MeCNs), whereas [Ru(DPAbpy)MeCN]2+ [DPAbpy = N-(2,2′-bipyridin-6-yl)-N,N-bis(pyridin-2-ylmethyl)amine] does not release MeCN. Furthermore, [Ru-(TQA)(MeCN)2]2+ is highly selective for release of the MeCN that is perpendicular to the plane of the two axial quinolines. Density functional theory calculations provide a clear explanation for the photodissociation behavior of these two complexes. Excitation by visible light and intersystem crossing leads to a six-coordinate 3MLCT state. Dissociation of acetonitrile can occur after internal conversion to a dissociative 3MC state, which has an occupied dσ* orbital that interacts in an antibonding fashion with acetonitrile. For [Ru(TQA)(MeCN)2]2+, the dissociative 3MC state is lower than the 3MLCT state. In contrast, the 3MC state of [Ru(DPAbpy)MeCN]2+ that releases acetonitrile has an energy higher than that of the 3MLCT state, indicating dissociation is unfavorable. These results are consistent with the experimental observations that efficient photodissociation of acetonitrile occurs for [Ru(TQA)(MeCN)2]2+ but not for [Ru(DPAbpy)MeCN]2+. For the release of the MeCN ligand in [Ru(TQA)(MeCN)2]2+ that is perpendicular to the axial quinoline rings, the 3MLCT state has an occupied quinoline π* orbital that can interact with a dσ* Ru–NCCH3 antibonding orbital as the Ru–NCCH3 bond is stretched and the quinolines bend toward the departing acetonitrile. This reduces the barrier for the formation of the dissociative 3MC state, leading to the selective photodissociation of this acetonitrile. By contrast, when the acetonitrile is in the plane of the quinolines or bpy, no interaction occurs between the ligand π* orbital and the dσ* Ru–NCCH3 orbital, resulting in high barriers for conversion to the corresponding 3MC structures and no release of acetonitrile.

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Section: Resultsmentioning

confidence: 99%

Selective Photodissociation of Acetonitrile Ligands in Ruthenium Polypyridyl Complexes Studied by Density Functional Theory

Mazumder

Endicott

et al. 2015

Inorg. Chem.

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“…25 On the basis of the difference in the decay of the 3 MLCT state and recovery of the ground state, it was shown that the rate of population of a 3 LF state from the 3 MLCT state increased by an order of magnitude in going from [Ru(6-Mebpy) 3 ] 2+ to the more sterically demanding [Ru-(Me 4 bpy) 3 ] 2+ , with 3 MLCT lifetimes of 1.6 and 0.16 ps, respectively. 25 Distortions around the metal lead to a decrease in the calculated energy of the 3 LF state by ~4000 cm −1 in [Ru(6-Mebpy) 3 ] 2+ and ~7000 cm −1 in [Ru(Me 4 bpy) 3 ] 2+ relative to that in [Ru(bpy) 3 ] 2+ . Therefore, while the 3 LF state lies above the 3 MLCT state in the latter, it falls below the 3 MLCT state in the former, resulting in fast 3 MLCT decay to populate the 3 LF state.…”

Section: Enhanced Photoinduced Ligand Exchange With Steric Bulkmentioning

confidence: 99%

“…These distortions reduce the orbital overlap and lower the energy of the e g -type orbitals, 15 thus decreasing the energy of the 3 LF states, sometimes below that of the 3 MLCT state. 25 …”

Section: Introductionmentioning

confidence: 99%

New Ru(II) Complexes for Dual Photoreactivity: Ligand Exchange and ¹O₂ Generation

2015

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CONSPECTUS Uncovering the factors that govern the electronic structure of Ru(II)–polypyridyl complexes is critical in designing new compounds for desired photochemical reactions, and strategies to tune excited states for ligand dissociation and 1O2 production are discussed herein. The generally accepted mechanism for photoinduced ligand dissociation proposes that population of the dissociative triplet ligand field (3LF) state proceeds through thermal population from the vibrationally cooled triplet metal-to-ligand charge transfer (3MLCT) state; however, temperature-dependent emission spectroscopy provides varied activation energies using the emission and ligand exchange quantum yields for [Ru(bpy)2(L)2]2+ (bpy = 2,2′-bipyridine; L = CH3CN or py). This suggests that population of the 3LF state proceeds from the vibrationally excited 3MLCT state. Because the quantum yield of ligand dissociation for nitriles is much more efficient than that for py, steric bulk was introduced into the ligand set to distort the pseudo-octahedral geometry and lower the energy of the 3LF state. The py dissociation quantum yield with 500 nm irradiation in a series of [Ru(tpy)(NN)(py)]2+ complexes (tpy = 2,2′:6′,2″-terpyridine; NN = bpy, 6,6′-dimethyl-2,2′-bipyridine (Me2bpy), 2,2′-biquinoline (biq)) increases by 2–3 orders of magnitude with the sterically bulky Me2bpy and biq ligands relative to bpy. Ultrafast transient absorption spectroscopy reveals population of the 3LF state within 3–7 ps when NN is bulky, and density functional theory calculations support stabilized 3LF states. Dual activity via ligand dissociation and 1O2 production can be achieved by careful selection of the ligand set to tune the excited-state dynamics. Incorporation of an extended π system in Ru(II) complexes such as [Ru(bpy)(dppn)(CH3CN)2]2+ (dppn = benzo[i]dipyrido[3,2-a:2′,3′-c]phenazine) and [Ru(tpy)(Me2dppn)(py)]2+ (Me2dppn = 3,6-dimethylbenzo[i]dipyrido[3,2-a:2′,3′-c]phenazine) introduces low-lying, long-lived dppn/Me2dppn 3ππ* excited states that generate 1O2. Similar to [Ru(bpy)2(CH3CN)2]2+, photodissociation of CH3CN occurs upon irradiation of [Ru(bpy)(dppn)(CH3CN)2]2+, although with lower efficiency because of the presence of the 3ππ* state. The steric bulk in [Ru(tpy)(Me2dppn)(py)]2+ is critical in facilitating the photoinduced py dissociation, as the analogous complex [Ru(tpy)(dppn)(py)]2+ produces 1O2 with near-unit efficiency. The ability to tune the relative energies of the excited states provides a means to design potentially more active drugs for photochemotherapy because the photorelease of drugs can be coupled to the therapeutic action of reactive oxygen species, effecting cell death via two different mechanisms. The lessons learned about tuning of the excited-state properties can be applied to the use of Ru(II)–polypyridyl compounds in a variety of applications, such as solar energy conversion, sensors and switches, and molecular machines.

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“…41 Since we were not able to optimize the 3 MC states (although we have tried several possible initial geometry guess and different approaches), here we will present a brief discussion on the qualitative aspects associated with the dark states and the X ligands chemical composition. One can expect that the energy of the 3 MC state can be tuned by X ligand modification and that the destabilization of the dark state should be in line with the -donor properties/HOMO energies of the isolated ligands.…”

Section: MC Dark State As a Photodeactivation Channelmentioning

confidence: 99%

Engineering Tunable Single and Dual Optical Emission from Ru(II)–Polypyridyl Complexes through Excited State Design

et al. 2017

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On the role of ligand-field states for the photophysical properties of ruthenium(II) polypyridyl complexes

Cited by 125 publications

References 88 publications

Selective Photodissociation of Acetonitrile Ligands in Ruthenium Polypyridyl Complexes Studied by Density Functional Theory

Selective Photodissociation of Acetonitrile Ligands in Ruthenium Polypyridyl Complexes Studied by Density Functional Theory

New Ru(II) Complexes for Dual Photoreactivity: Ligand Exchange and ¹O₂ Generation

Engineering Tunable Single and Dual Optical Emission from Ru(II)–Polypyridyl Complexes through Excited State Design

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On the role of ligand-field states for the photophysical properties of ruthenium(II) polypyridyl complexes

Cited by 125 publications

References 88 publications

Selective Photodissociation of Acetonitrile Ligands in Ruthenium Polypyridyl Complexes Studied by Density Functional Theory

Selective Photodissociation of Acetonitrile Ligands in Ruthenium Polypyridyl Complexes Studied by Density Functional Theory

New Ru(II) Complexes for Dual Photoreactivity: Ligand Exchange and 1O2 Generation

Engineering Tunable Single and Dual Optical Emission from Ru(II)–Polypyridyl Complexes through Excited State Design

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Product

Resources

About

New Ru(II) Complexes for Dual Photoreactivity: Ligand Exchange and ¹O₂ Generation