Solid-Phase Synthesis as a Platform for the Discovery of New Ruthenium Complexes for Efficient Release of Photocaged Ligands with Visible Light

Sharma, Rajgopal; Knoll, Jessica D.; Ancona, Nicholas; Martin, Phillip; Turró, Claudia; Kodanko, Jeremy J.

doi:10.1021/ic502791y

Cited by 21 publications

(29 citation statements)

References 104 publications

(193 reference statements)

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“…A comparison between the bond angles of 1 and 2 reveals that the only difference is that in 2 the N6 CH 3 CN cis to the basic amine nitrogen is tilted slightly toward the N2 arm, as evidenced by the slightly smaller N6–Ru1–N2 angle of 86.99(3)° in 2 as compared to 93.00(7)° in 1 . Again, the Ru–N bond lengths in 2 are comparable to 1 , as well as to those of the previously reported [Ru(TQA)(CH 3 CN) 2 ] 2+ 58 . In addition, the Ru–N(CH 3 CN) bond lengths in 2 also compare well with those reported for cis -[Ru(bpy) 2 (CH 3 CN) 2 ] 2+ 88.…”

Section: Resultssupporting

confidence: 87%

“…Like [Ru(TPA)(CH 3 CN) 2 ] 2+ and [Ru(TPA)(py) 2 ] 2+ , irradiation of [Ru(TQA)(CH 3 CN) 2 ] 2+ only results in ligand exchange of the CH 3 CN positioned cis to the basic amine nitrogen of the TQA ligand. 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: 98%

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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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Section: Resultssupporting

confidence: 87%

Section: Introductionmentioning

confidence: 98%

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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“…44 In an effort to tune the photochemistry of the Ru(TPA) caging group, ligands derived from TPA were designed and analyzed for photochemical reactivity of Ru(II) nitrile complexes. 45 Results revealed that absorptivity is shifted readily into the visible range upon tuning the ligand structure. However, a wide range of reactivities with light was observed for complexes derived from very similar ligands, even though several complexes absorbed light in the visible range.…”

Section: Introductionmentioning

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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“…48 Briefly, Ru(II)-caged MeCN complexes were synthesized using a library of TPA derivatives obtained on polystyrene resin, which were then metalated using fac -[Ru(DMSO) 3 (O 2 CCCF 3 ) 2 (H 2 O)], converted into caged nitriles upon treatment with MeCN/H 2 O, and cleaved from the resin for photochemical analysis (Figure 4). The data show a wide range of spectral tuning and reactivity with visible light for these complexes.…”

Section: The Development Of Ru(tpa) For Photocagingmentioning

confidence: 99%

“…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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Solid-Phase Synthesis as a Platform for the Discovery of New Ruthenium Complexes for Efficient Release of Photocaged Ligands with Visible Light

Cited by 21 publications

References 104 publications

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

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

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

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

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