Bistridentate ruthenium(II)polypyridyl-type complexes with microsecond 3MLCT state lifetimes: Sensitizers for rod-like molecular arrays

Maria Abrahamsson, Michael Jäger, Rohan J. Kumar, Tomas Österman, Petter Persson, Hans Christian Becker, Olof Johansson, Leif Hammarström

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153 Citations (Scopus)

Abstract

A series of bistridentate ruthenium(II) polypyridyl-type complexes based on the novel 2,6-di(quinolin-8-yl)pyridine (dqp) ligand have been synthesized and their photophysical properties have been studied. The complexes are amenable to substitution in the 4-position of the central pyridine with conserved quasi-C2v symmetry, which allows for extension to isomer-free, rod-like molecular arrays for vectorial control of electron and energy transfer. DFT calculations performed on the parent [Ru(dqp)2]2+ complex (1) predicted a more octahedral structure than in the typical bistridentate complex [Ru(tpy)2]2+ (tpy is 2,2′:6′,2″-terpyridine) thanks to the larger ligand bite angle, which was confirmed by X-ray crystallography. A strong visible absorption band, with a maximum at 491 nm was assigned to a metal-to-ligand charge transfer (MLCT) transition, based on time-dependent DFT calculations. 1 shows room temperature emission (Φ = 0.02) from its lowest excited ( 3MLCT) state that has a very long lifetime (τ = 3 μs). The long lifetime is due to a stronger ligand field, because of the more octahedral structure, which makes the often dominant activated decay via short-lived metal-centered states insignificant also at elevated temperatures. A series of complexes based on dqp with electron donating and/or accepting substituents in the 4-position of the pyridine was prepared and the properties were compared to those of 1. An unprecedented 3MLCT state lifetime of 5.5 μs was demonstrated for the homoleptic complex based on dqpCO2Et. The favorable photosensitizer properties of 1, such as a high extinction coefficient, high excited-state energy and long lifetime, and tunable redox potentials, are maintained upon substitution. In addition, the parent complex 1 is shown to be remarkably photostable and displays a high reactivity in light-induced electron and energy transfer reactions with typical energy and electron acceptors and donors: methylviologen, tetrathiofulvalene, and 9,10-diphenylanthracene. This new class of complexes constitutes a promising starting point for the construction of linear, rod-like molecular arrays for photosensitized reactions and applications in artificial photosynthesis and molecular electronics.

Original languageEnglish
Pages (from-to)15533-15542
Number of pages10
JournalJournal of the American Chemical Society
Volume130
Issue number46
DOIs
Publication statusPublished - Nov 19 2008

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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