Excited-State Acid−Base Chemistry:  Evidence for a Dissociative Excited State

Fan, Jianwei; Helmy, Roy; Kassis, Abe; Grunseich, Amanda; Mangubat, Peter; Hicks, Charles H.; Stevens, Nathan; Gafney, Harry D.

doi:10.1021/ic030055c

Cited by 3 publications

(6 citation statements)

References 11 publications

(21 reference statements)

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“…The eluent was evaporated to dryness, dissolved in a minimum of acetonitrile, and the complex was purified using an alumina column and eluting with acetonitrile. At wavelengths g350 nm, absorption and emission spectra of the nitrate salt are identical to those of PF 6 -and ClO 4 -salts, 8 and, within an experimental uncertainty of 10%, the emission lifetime of the complex in room temperature, aqueous solution is independent of the counteranion. Physical Measurements.…”

Section: Experimental Methodsmentioning

confidence: 65%

“…On the basis of a pK a of 1.12, at pH 5, g99.99% of the complex is present as Ru(bpy) 2 (dpp) 2+ , and the emission spectrum consists of only the 705 nm emission from the unprotonated complex. Taking the quantum efficiency of emission from room temperature, 22 ( 1°C, N 2 saturated, aqueous solutions of Ru(bpy) 3 2+ in water (6) to be 0.0429 (averaged from several references 18 ), the gradient method using a series of concentrations e0.10M 11 yields 1.98 ( 0.20 × 10 -3 as the quantum efficiency of the 705 nm emission from the unprotonated complex Ru(bpy) 2 (dpp) 2+ , designated Φ em u . The 735 nm emission from the protonated complex was then measured from a deaerated, aqueous solution containing the same concentration of Ru(bpy) 2 (dpp) 2+ but 1.0 M in HNO 3 .…”

Section: Nm Emissionmentioning

confidence: 99%

“…5 The [H + ] dependence of the quantum yield of dissociation of the bimetallic [bpy) 2 Ru(CN)(µ-CN)Rh(NH 3 ) 4 Br] 2+ and the appearance of a (bpy) 2 Ru(CN) 2 emission from a bimetallic composed of two components that, as individual molecules quench at a diffusion controlled rate, led to the suggestion that optical excitation of the (bpy) 2 Ru(CN) 2 ligand in [bpy) 2 Ru(CN)(µ-CN)Rh(NH 3 ) 4 Br] 2+ leads to a dissociative excited state. 6 Dissociation is attributed to the reduction in electron density at the cyano groups as evidenced by the decrease in their basicity on the population of the (bpy) 2 Ru(CN) 2 ligand's MLCT state.…”

Section: Introductionmentioning

confidence: 99%

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Excited-State Coordination Chemistry: Excited-State Basicity of Bis(2,2′-bipyridyl)(2,3-dipyridylpyrazine)ruthenium(II)

2009

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The proton dependencies of the absorption and emission spectra of bis(2,2′-bipyridyl)(2,3-bis(2-pyridyl)pyrazine)ruthenium(II), (bpy) 2 Ru(dpp) 2+ indicate that population of the dpp-localized MLCT state increases the basicity of dpp peripheral nitrogens. NMR spectra reveal the protonation of the peripheral dpp pyridine in the ground state, pK a of 1.12 ( 0.03, occurs intermediate between the changes evident in the absorption and emission spectra. As a result, the emissivity of aqueous solutions of (bpy) 2 Ru(dpp) 2+ as a function of [H + ] derives from two emissive species: the unprotonated complex and the monoprotonated complex [(bpy) 2 Ru(dppH py )] 3+ with the proton attached to the peripheral dpp pyridine. Although protonation in the MLCT state generally quenches the emission, the emissivity of the monoprotonated complex, albeit weak, is attributed to the asymmetric distribution of the charge in the MLCT state. The majority of the transferred charge resides at the peripheral pyrazinyl nitrogen, and excited-state acid-base chemistry occurs predominantly at this site. Nonetheless, ground-state protonation of the peripheral dpp pyridine dramatically increases the nonradiative decay rate and significantly influences subsequent excited-state protonation processes. Protonation of the excited state changes from a bimolecular process to a combination of inter-and intramolecular processes where the proton transfers from the dpp pyridyl nitrogen to the dpp pyrazinyl nitrogen and from the surrounding aqueous solvent shell. Energetically, changes in the absorption spectra originally attributed to the first protonation of the complex and from which the ∆pK a of the excited state have been estimated, in fact, correspond to the second protonation of the complex. IntroductionThe hydrogen ion dependencies of the absorption and emission spectra of Ru(II) diimines reveal substantial differences in the acid-base properties of the ground and emissive MLCT states of the complexes. 1 Depending on the direction of the charge transfer relative to the acid-base site, and the location of the acceptor orbital in the MLCT state, excitation changes electron distribution, which in turn increases or decreases acid-base properties by as much as 5 to 6 orders of magnitude. 2 Brønsted basicity usually does not correlate with the coordinating ability of a ligand, but, with diimine ligands, the equilibrium constant for coordination increases linearly with the Brønsted basicity of the ligand's coordinating nitrogens. 3 Work in this laboratory focuses on whether these photoinduced changes in acid-base properties translate into an excited-state coordination chemistry where a Ru(II) diimine possessing one or more acid-base sites on the ligand periphery functions as a ligand and whether excitation enhances or reduces its ability to coordinate to another metal.Excited-state coordination chemistry arises from the observation that excitation of bis(2,2′-bipyridyl)(2,3-dipyridylpyrazine)ruthenium(II), (bpy) 2 Ru(dpp) 2+ , in the presence of PtCl 6

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Section: Experimental Methodsmentioning

confidence: 65%

Section: Nm Emissionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Excited-State Coordination Chemistry: Excited-State Basicity of Bis(2,2′-bipyridyl)(2,3-dipyridylpyrazine)ruthenium(II)

2009

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“…13 Likewise, precedents of startling basicity or nucleophilicity upon photoexcitation leading to excited-state ligation are also known, most notably by Gafney et al for d 6 imine complexes. 14 In conclusion, the work here illustrates the feasibility of systematic tuning of the emission color by controlling the steric bulk in three-coordinate excited states of Au(I) complexes. MOLED applications are being pursued based on these findings because of desired emission properties that include brightness, stability, and phosphorescence with short triplet lifetimes.…”

mentioning

confidence: 66%

Beyond a T-Shape

2005

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Varying the steric bulk of either the phosphine or the halide in Au(PR3)2X complexes allows intuitive tuning of the phosphorescence energy to multiple visible colors, including the coveted blue for LED applications. The excited-state structure involves distortion of the trigonal coordination sphere beyond a T-shape. The [Au(TPA)2]Cl complex exhibits orange phosphorescence due to exciplex formation with the counterion to form the same type of excited state, representing the first example of a luminescent two-coordinate Au(I) complex in absence of both Au...Au interactions and aromatic moieties.

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“…The remarkable feature of this bimetallic complex is that the dissociated 3 Ru(bpy) 2 (CN) 2 fragment remains excited. 13 Investigation of systems containing Ru(bpy) 2 (CN) 2 and silver ion in MeCN indicated the formation of more than two species containing the Ru(II) complex and Ag + constituents. Whitten and Kinnard 14 estimated the formation constant of [Ag (NC)Ru(bpy) 2 (CN)] + , [(NC)Ru(bpy) 2 (CN)Ag (NC)Ru(bpy) 2 (CN)] + and [Ag(NC)Ru(bpy) 2 (CN)Ag] 2+ and revealed the appearance of polynuclear complexes by absorption and emission spectroscopy and luminescence lifetime measurements.…”

Section: Introductionmentioning

confidence: 99%

Polynuclear complexes of a dissociative excited state formed in the [Ru(bpy)2(CN)2]–HgCl2 system

Fodor-Kardos

Horváth

2005

Photochem Photobiol Sci

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The complex cis-dicyanobis(2,2'-bipyridine)ruthenium(II) forms various bimetallic complexes with mercury(II)chloride, such as [(NC)Ru(bpy)2(CN)-HgCl2], [Cl2Hg-(NC)Ru(bpy)2(CN)-HgCl2-(NC)Ru(bpy)2(CN)-HgCl2] and [Cl2Hg-(NC)Ru(bpy)2(CN)-(HgCl2)] in CH3CN. These polynuclear complexes of the equilibrium system have been identified and characterized by their formation constants and absorption spectra. Excitation of bimetallic complexes produces the MLCT state localized on [Ru(bpy)2(CN)2] ligand, resulting in the cleavage of the bond formed between the nitrogen atom of the coordinated cyanide ligand and the Hg(II) central atom in ground state. Unlike many photoinduced metal ligand dissociations, the dissociated fragment remains in a luminescent excited state.

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Excited-State Acid−Base Chemistry: Evidence for a Dissociative Excited State

Cited by 3 publications

References 11 publications

Excited-State Coordination Chemistry: Excited-State Basicity of Bis(2,2′-bipyridyl)(2,3-dipyridylpyrazine)ruthenium(II)

Excited-State Coordination Chemistry: Excited-State Basicity of Bis(2,2′-bipyridyl)(2,3-dipyridylpyrazine)ruthenium(II)

Beyond a T-Shape

Polynuclear complexes of a dissociative excited state formed in the [Ru(bpy)2(CN)2]–HgCl2 system

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