A ππ State Enables Photoaccumulation of Charges on a π‑Extended Dipyridophenazine Ligand in a Ru(II) Polypyridine Complex

The π-extended dipyrido­[3,2-a:2′,3′-c]­phenazine (dppz) ligand of the Ru­(II) complex [Ru­(bpy)2(oxo-dppqp)]­(PF6)2 (oxo-dppqp = dipyrido­[3,2-a:2′,3′-c]­pyrido­[2″,3″-4,5,6]­quinolino­[2,3-h]­phenazin-15-one, bpy = 2,2′-bipyridine) enables the mononuclear complex for visible-light-driven accumulat...

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Published in:Journal of physical chemistry. C 2018-01, Vol.122 (1), p.83-95
Main Authors: Schindler, Julian, Zhang, Ying, Traber, Philipp, Lefebvre, Jean-François, Kupfer, Stephan, Demeunynck, Martine, Gräfe, Stefanie, Chavarot-Kerlidou, Murielle, Dietzek, Benjamin
Format: Article
Language:English
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Summary:The π-extended dipyrido­[3,2-a:2′,3′-c]­phenazine (dppz) ligand of the Ru­(II) complex [Ru­(bpy)2(oxo-dppqp)]­(PF6)2 (oxo-dppqp = dipyrido­[3,2-a:2′,3′-c]­pyrido­[2″,3″-4,5,6]­quinolino­[2,3-h]­phenazin-15-one, bpy = 2,2′-bipyridine) enables the mononuclear complex for visible-light-driven accumulation of two electrons on a single ligand structure. Although this has been shown before, the excited-state physics underlying this promising feature are exploited in this work. The photophysics of the complex was investigated by excitation-wavelength-dependent resonance Raman and transient absorption spectroscopy in combination with time-dependent density functional theory. The results show that excitation with visible light leads to the population of the two excited-state branches: (i) the population of a short-lived 3MLCT state in which the excess electronic density is localized on the pyridoquinolinone moiety of the extended ligand (τ = 105 ps) and (ii) the population of a more long-lived 3ππ* state (τ = 9 ns). Notably, the long-lived 3ππ* state rather than a 3MLCT state is prone to reductive quenching by the sacrificial electron donor and, hence, presents the critical excited-state intermediate in the photochemical charge accumulation experiments.
ISSN:1932-7447
1932-7455
DOI:10.1021/acs.jpcc.7b08989