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Issue 30, 2017
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Frontier orbitals of photosubstitutionally active ruthenium complexes: an experimental study of the spectator ligands’ electronic properties influence on photoreactivity

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Abstract

The synthesis and characterization of [Ru(tpy)(R2bpy)(L)](X)n complexes (tpy = 2,2′:6′,2′′-terpyridine, R2bpy = 4,4′-dimethyl-2,2′-bipyridine (dmbpy), or 4,4′-bis(trifluoromethyl)-2,2′-bipyridine (tfmbpy), X = Cl or PF6, and n = 1 or 2) are described. The dmbpy and tfmbpy bidentate ligands allow for investigating the effects of electron-donating and electron-withdrawing ligands, respectively, on the frontier orbital energetics as well as the photoreactivity of these ruthenium polypyridyl complexes for five prototypical monodentate ligands L = Cl, H2O, CH3CN, 2-(methylthio)ethanol (Hmte), or pyridine. According to spectroscopic and electrochemical studies, the dmbpy analogues displayed a singlet metal-to-ligand charge transfer (1MLCT) transition at higher energy than the tfmbpy analogues. The shift of the 1MLCT to higher energy results from the lowest unoccupied molecular orbital (LUMO) for the dmbpy analogues being tpy-based, whereas for the tfmbpy analogues orbital inversion occurs resulting in a tfmbpy-based LUMO. The energy level of the highest occupied molecular orbital (HOMO) was considerably affected by the nature of the monodentate ligand. Visible light irradiation of the complexes demonstrated that the tfmbpy analogue increased the rate and quantum yields of photosubstitution reactions, compared to the dmbpy analogue, suggesting that the electron-withdrawing substituents allowed better thermal accessibility of the triplet metal-centered (3MC) state from the photochemically generated triplet metal-to-ligand charge transfer (3MLCT) excited state. A correlation between the photolability of the monodentate ligands and the electrochemical reversibility of the metal-based oxidation is also reported.

Graphical abstract: Frontier orbitals of photosubstitutionally active ruthenium complexes: an experimental study of the spectator ligands’ electronic properties influence on photoreactivity

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Publication details

The article was received on 27 Apr 2017, accepted on 12 Jul 2017 and first published on 20 Jul 2017


Article type: Paper
DOI: 10.1039/C7DT01540B
Citation: Dalton Trans., 2017,46, 9969-9980
  • Open access: Creative Commons BY-NC license
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    Frontier orbitals of photosubstitutionally active ruthenium complexes: an experimental study of the spectator ligands’ electronic properties influence on photoreactivity

    H. J. Jang, S. L. Hopkins, M. A. Siegler and S. Bonnet, Dalton Trans., 2017, 46, 9969
    DOI: 10.1039/C7DT01540B

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