Novel Ru(II)/Os(II)‐Exchange Homo‐ and Heterometallic Polypyridyl Complexes with Effective Energy Transfer

Abstract

Two novel homometallic Ru−Ru and heterometallic Ru−Os dimers and trimers, [MII(bpy)2(4‐tpy‐4′‐methyl‐2,2′‐bipyridine)MII(tpy)]4+ and [MII(bpy)2](4‐tpy‐4′‐tpy‐2,2′‐bipyridine)(MII(tpy))2]6+, have been first prepared and characterized. Electrochemical properties of the metal‐based reversible oxidation and ligand‐based reduction are measured. Spectroscopic analysis of these complexes exhibits for every Ru‐ or Os‐based subunit an individual intense absorption spectrum extended over the entire UV and visible region. The heteronuclear complexes [RuII(bpy)2(4‐tpy‐4′‐methyl‐2,2′‐bipyridine)OsII(tpy)]4+, [RuII(bpy)2](4‐tpy‐4′‐tpy‐2,2′‐bipyridine)(OsII(tpy))2]6+, and [OsII(bpy)2](4‐tpy‐4′‐tpy‐2,2′‐bipyridine)(RuII(tpy))2]6+ display a weak emission spectrum in the near‐infrared region (NIR). The luminescence of the polynuclear assemblies is quantitatively quenched, by intramolecular energy transfer to the lower‐lying metal‐to‐ligand charge transfer (3MLCT) and metal‐centered (3MC) state of the Os(II)‐based center or Ru(II)‐terpyridine moiety at room temperature.

Effect of electronic structure of energy transfer in bimetallic Ru(ii)/Os(ii) complexes

“…However, monometallic (μ-LL′)Ru presents only two 2,2′-bipyridine reduction waves at around −1.35 and −1.55 V. Ru(μ-L 2 L 2′ )Ru displays five reduction peaks, the first four reductions at −1.15, −1.32, −1.44 and −1.54 V are assigned to successive reductions of the simple 2,2′-bipyridine ligands, and the last at −1.76 V can be assigned to the 2,2′-bipyridine moiety on the bridging ligand L 2 L 2′ . 33 Ru(μ-L 1 L 1′ )Ru shows only two reduction waves of 2,2′-bipyridine moieties at −1.27, −1.50 V. Ru(μ-L 1 L 1′ )Os displays successive reduction processes of two simple 2,2′-bipyridine ligands at around −1.35 and −1.50 V, and another at −1.75 V, which can be assigned to the 2,2′-bipyridine moiety of L 2 L 2′ . Similarly, for Os(μ-LL′)Ru dinuclear complexes, the first and third reductions can be assigned to the two 2,2′-bipyridine moieties, the second potential present one reduction process of two electrons of two 2,2′-bipyridine moieties.…”

Probing the effect of nitro-substituents in the modulation of LUMO energies for directional electron transport through 4d6ruthenium(ii)-based metallosurfactants

“…Upon coordination to the metal center, the terpy ligand adopts a cis : cis type orientation, 24 and as a result, most of terpy OC18 ligand peaks of these species show an upfield peak shift in their NMR spectrum. 25 Complexes 1 and 2 show the expected symmetric signals in the 1 H-NMR spectrum owing to the presence of C 2V ligand environments around the metal center. In compounds 3 and 4 , a significant downfield shift was observed for proton H29 of the phenanthroline, compared to its corresponding peak position in the free ligand.…”

“…These potentials indicate that the nitro group brings the Ru 2+ /Ru 3+ couple to a more positive value. 25 The noticeable shift of ca . 0.50 V in species 3 and 4 is attributed to the σ donor ability of the chloride ligand, which increases the electron density around the metal center.…”

“…Upon coordination to the metal center, the terpy ligand adopts a cis:cis type orientation, 24 and as a result, most of terpy OC18 ligand peaks of these species show an upfield peak shift in their NMR spectrum. 25 Complexes 1 and 2 show the expected symmetric signals in the 1 H-NMR spectrum owing to the pres-…”

Ru(II)–Ru(II) and Ru(II)–Os(II) Homo-/Heterodinuclear Complexes and Ru3(II)–Ru(II) Homotetranuclear Complexes Based on Heteroditopic Bridging Ligands: Synthesis, Photophysics, and Effective Energy Transfer

“…40,41 Therefore, new NIR-emitting dyes with improved photophysical properties are still desirable. Recently, our group 38 reported two novel homometallic Ru−Ru and heterometallic Ru−Os dimers and trimers, the absorption spectra of which covered the entire UV and visible regions.…”