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

Tu, Yi Jung; Mazumder, Shivnath; Endicott, John F.; Turró, Claudia; Kodanko, Jeremy J.; Schlegel, H. Bernhard

doi:10.1021/acs.inorgchem.5b01202

Cited by 42 publications

(54 citation statements)

References 63 publications

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“…Loss of CH 3 CN from N6 leads to 3 MC 1 , a trigonal bipyramidal complex (with N3–Ru–N1 as the axis) that is 5 kcal/mol more stable than the loss of CH 3 CN from N1 which forms 3 MC 2 , a square pyramidal structure (with Ru–N3 as the axis). 28 These results are in good agreement with previous observations, 25 which showed that photochemical dissociation of the N6 CH 3 CN is significantly more facile than the N1 CH 3 CN for Ru-quinoline and Ru-bipyridine complexes. 28 The N6 CH 3 CN was found to be more labile than the N1 CH 3 CN in the triplet excited states because of a favorable orbital mixing between the aromatic ligand π * and the Ru d σ * orbitals that characterize the Ru–N6 CH 3 CN dissociation.…”

Section: Computational Chemistrysupporting

confidence: 92%

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Effects of Methyl Substitution in Ruthenium Tris(2-pyridylmethyl)amine Photocaging Groups for Nitriles

et al. 2016

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Four complexes of the general formula [Ru(L)(CH3CN)2](PF6)2, [L = TPA (5), MeTPA (6), Me2TPA (7), and Me3TPA (8)] [TPA = tris[(pyridin-2-yl)methyl]amine, where methyl groups were introduced consecutively onto the 6-position of py donors of TPA, were prepared and characterized by various spectroscopic techniques and mass spectrometry. While 5 and 8 were isolated as single stereoisomers, 6 and 7 were isolated as mixtures of stereoisomers in 2:1 and 1.5:1 ratios, respectively. Steric effects on ground state stability and thermal and photochemical reactivities were studied for all four complexes using 1H NMR and electronic absorption spectroscopies and computational studies. These studies confirmed that the addition of steric bulk accelerates photochemical and thermal nitrile release.

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Section: Computational Chemistrysupporting

confidence: 92%

“…6,7 Metal complexes also bind to functional groups that cannot be caged with organic fragments, including nitrogen-containing heterocycles, 8–15 thioethers 16–18 and nitriles. 19–28 Thus, metal complexes offer an orthogonal approach to organic caging methods.…”

Section: Introductionmentioning

confidence: 99%

Effects of Methyl Substitution in Ruthenium Tris(2-pyridylmethyl)amine Photocaging Groups for Nitriles

et al. 2016

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“…58 Calculations provided an explanation for the increase and selectivity of ligand exchange, showing the presence of favorable orbital overlap in the excited state between the coplanar quinoline arms of the TQA ligand and the photolabile CH 3 CN ligand that is not present in the TPA complex. 59 …”

Section: Introductionmentioning

confidence: 99%

Unusual Role of Excited State Mixing in the Enhancement of Photoinduced Ligand Exchange in Ru(II) Complexes

Loftus

Fillman

et al. 2017

J. Am. Chem. Soc.

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Four Ru(II) complexes were prepared bearing two new tetradentate ligands, cyTPA and 1-isocyTPQA, which feature a piperidine ring that provides a structurally rigid backbone and facilitates the installation of other donors as the fourth chelating arm, while avoiding the formation of stereoisomers. The photophysical properties and photochemistry of [Ru(cyTPA)(CH3CN)2]2+ (1), [Ru(1-isocyTPQA)(CH3CN)2]2+ (2), [Ru(cyTPA)(py)2]2+ (3), and [Ru(1-isocyTPQA)-(py)2]2+ (4) were compared. The quantum yield for the CH3CN/H2O ligand exchange of 2 was measured to be Φ400 = 0.033(3), 5-fold greater than that of 1, Φ400 = 0.0066(3). The quantum yields for the py/H2O ligand exchange of 3 and 4 were lower, 0.0012(1) and 0.0013(1), respectively. DFT and related calculations show the presence of a highly mixed 3MLCT/3ππ* excited state as the lowest triplet state in 2, whereas the lowest energy triplet states in 1, 3, and 4 were calculated to be 3LF in nature. The mixed 3MLCT/3ππ* excited state places significant spin density on the quinoline moiety of the 1-isocyTPQA ligand positioned trans to the photolabile CH3CN ligand in 2, suggesting the presence of a trans-type influence in the excited state that enhances ligand exchange. Ultrafast spectroscopy was used to probe the excited states of 1–4, which confirmed that the mixed 3MLCT/3ππ* excited state in 2 promotes ligand dissociation, representing a new manner to effect photoinduced ligand exchange. The findings from this work can be used to design improved complexes for applications that require efficient ligand dissociation, as well as for those that require minimal deactivation of the 3MLCT state through low-lying metal-centered states.

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“…Thus, it is generally accepted that ligands coordinated to the metal center can be easily dissociated upon irradiation with light at room temperature through population of the 3LF state(s). 27,33,43 In addition, caged molecules are released as a primary photochemical step, thus avoiding undesirable photo-damage that commonly occurs from organic photocages arising from dark reactions. 1,43–46 The three-dimensional geometry and tunable photophysical properties also make Ru(II) polypyridyl complexes attractive photocaging agents.…”

Section: Introductionmentioning

confidence: 99%

“…27,33,43 In addition, caged molecules are released as a primary photochemical step, thus avoiding undesirable photo-damage that commonly occurs from organic photocages arising from dark reactions. 1,43–46 The three-dimensional geometry and tunable photophysical properties also make Ru(II) polypyridyl complexes attractive photocaging agents. 27,46–48 …”

Section: Introductionmentioning

confidence: 99%

Ru(II) Polypyridyl Complexes Derived from Tetradentate Ancillary Ligands for Effective Photocaging

Turró

Kodanko

2018

Acc. Chem. Res.

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CONSPECTUS Metal complexes have many proven applications in the caging and photochemical release of biologically active compounds. Photocaging groups derived from Ru(II) traditionally have been composed of ancillary ligands that are planar and bi- or tridentate, such as 2,2′-bipyridine (bpy), 2,2′:6′,2″-terpyridine (tpy), and 1,10-phenanthroline (phen). Complexes bearing ancillary ligands with denticities higher than three represent a new class of Ru(II)-based photocaging groups that are grossly underdeveloped. Because high-denticity ancillary ligands provide the ability to increase the structural rigidity and control the stereochemistry, our groups initiated a research program to explore the applications of such ligands in Ru(II)-based photocaging. Ru(TPA), bearing the tetradentate ancillary ligand tris(2-pyridylmethyl)amine (TPA), has been successfully utilized to effectively cage nitriles and aromatic heterocycles. Nitriles and aromatic heterocycles caged by the Ru(TPA) group show excellent stability in aqueous solutions in the dark, and the complexes can selectively release the caged molecules upon irradiation with light. Ru(TPA) is applicable as a photochemical agent to offer precise spatiotemporal control over biological activity without undesired toxicity. In addition, Ru(II) polypyridyl complexes with desired photochemical properties can be synthesized and identified by solid-phase synthesis, and the resulting complexes show properties to similar to those of complexes obtained by solution-phase synthesis. Density functional theory (DFT) calculations reveal that orbital mixing between the π* orbitals of the ancillary ligand and the Ru−N dσ* orbital is essential for ligand photodissociation in these complexes. Furthermore, the introduction of steric bulk enhances the photoliability of the caged molecules, validating that steric effects can largely influence the quantum efficiency of photoinduced ligand exchange in Ru(II) polypyridyl complexes. Recently, two new photocaging groups, Ru(cyTPA) and Ru(1-isocyTPQA), have been designed and synthesized for caging of nitriles and aromatic heterocycles, and these complexes exhibit unique photochemical properties distinct from those derived from Ru(TPA). Notably, the unusually greater quantum efficiency for the ligand exchange in [Ru(1-isocyTPQA)(MeCN)2](PF6)2, Φ400 = 0.033(3), uncovers a trans-type effect in the triplet metal-to-ligand charge transfer (3MLCT) state that enhances photoinduced ligand exchange in a new manner. DFT calculations and ultrafast transient spectroscopy reveal that the lowest-energy triplet state in [Ru(1-isocyTPQA)(MeCN)2](PF6)2 is a highly mixed 3MLCT/3ππ* excited state rather than a triplet metal-centered ligand-field (3LF) excited state; the latter is generally accepted for ligand photodissociation. In addition, Mulliken spin density calculations indicate that a majority of the spin density in [Ru(1-isocyTPQA)(MeCN)2](PF6)2 is localized on the isoquinoline arm, which is opposite to the cis MeCN, rather than on the ruthenium center. This ...

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

Cited by 42 publications

References 63 publications

Effects of Methyl Substitution in Ruthenium Tris(2-pyridylmethyl)amine Photocaging Groups for Nitriles

Effects of Methyl Substitution in Ruthenium Tris(2-pyridylmethyl)amine Photocaging Groups for Nitriles

Unusual Role of Excited State Mixing in the Enhancement of Photoinduced Ligand Exchange in Ru(II) Complexes

Ru(II) Polypyridyl Complexes Derived from Tetradentate Ancillary Ligands for Effective Photocaging

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