Resonance Raman and time‐resolved resonance Raman spectra of the monomeric and dimeric complexes of ruthenium(II) with 2,3‐bis(2‐pyridyl)pyrazine (dpp)

Su, Hongbo; Kincaid, James R.

doi:10.1002/jrs.1074

Cited by 9 publications

(4 citation statements)

References 51 publications

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“…These results complement resonance Raman spectroscopy 21 and collectively indicate that the charge transferred in the MLCT to dpp is principally localized at the dpp pyrazinyl group. The minimal involvement of the pendant pyridine is attributed to its orthogonality to the coordinated portion of dpp.…”

Section: Discussionsupporting

confidence: 69%

“…The second protonation occurs at the pyrazinyl nitrogen and, as a component of that portion of dpp coordinated to Ru(II) produces a larger change in the MLCT transition energy, ∆E ) 2900 cm -1 , relative to that which occurs on protonation of peripheral dpp pyridine, ∆E ) 600 cm -1 . These results complement resonance Raman spectroscopy 21 and collectively indicate that the charge transferred in the MLCT to dpp is principally localized at the dpp pyrazinyl group. The minimal involvement of the pendant pyridine is attributed to its orthogonality to the coordinated portion of dpp.…”

Section: Discussionsupporting

confidence: 69%

“…Therefore, the third factor is that excitation of the unprotonated complex may also lead to formation of the monoprotonated complex at the pyridyl nitrogen in the excited state. This is possible because Su and Kincaid have shown using resonance Raman that electron redistribution upon population of the MLCT is primarily to the pyrazine portion of the dpp, but is asymmetric with a finite, small portion onto the pendant pyridyl ring . This portion may be sufficient to translate into an enhanced basicity in the excited state.…”

Section: Discussionmentioning

confidence: 99%

“…This is possible because Su and Kincaid have shown using resonance Raman that electron redistribution upon population of the MLCT is primarily to the pyrazine portion of the dpp, but is asymmetric with a finite, small portion onto the pendant pyridyl ring. 21 This portion may be sufficient to translate into an enhanced basicity in the excited state.…”

Section: Scheme 1: Proposed Model For the Ground-and Excited-state Prmentioning

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: Discussionsupporting

confidence: 69%

Section: Discussionsupporting

confidence: 69%

Section: Discussionmentioning

confidence: 99%

Section: Scheme 1: Proposed Model For the Ground-and Excited-state Prmentioning

confidence: 99%

See 2 more Smart Citations

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

2009

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Applications in Coordination Chemistry

Nakamoto

2008

Infrared and Raman Spectra of Inorganic and Coordination Compounds

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Spectator ligand effects on the vibrational spectra of heteroleptic complexes of ruthenium with bipyrazine

Kincaid

2004

J Raman Spectroscopy

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Resonance Raman (RR) and transient resonance Raman (TR 2 ) spectra were acquired for a series of heteroleptic complexes of ruthenium, i.e. RuL 2 (bpz) 2+ , where bpz is 2,2 -bipyrazine and L is 2,2 -bipyridine (bpy) or an alkylated 2,2 -bipyridine [i.e. diazafluorene (daf) or 4,4 -dimethyl-5,5 -diethyl-2,2 -bipyridine (dmdeb)]. Resonance Raman spectra acquired at different excitation wavelengths for the ground-state complexes reveal selective enhancement of modes associated with the coordinated bpz or the spectator ligands, as expected. The TR 2 spectra, acquired with excitation at 355 nm, confirm selective population of a bpz-localized 3 MLCT excited state for each complex. Both the ground-state RR spectra and the excited state TR 2 data indicate that only slight shifts are observed in a few modes as the donor strengths of the spectator ligands are varied. Such data for a systematically manipulated set of complexes, acquired here for the first time, imply that both the RR and TR 2 spectral parameters are reliably characteristic for a given ligand, varying only slightly as the nature of other ligands in the complex is changed.

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Resonance Raman and time‐resolved resonance Raman spectra of the monomeric and dimeric complexes of ruthenium(II) with 2,3‐bis(2‐pyridyl)pyrazine (dpp)

Cited by 9 publications

References 51 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)

Applications in Coordination Chemistry

Spectator ligand effects on the vibrational spectra of heteroleptic complexes of ruthenium with bipyrazine

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