Trifluoromethyl-substituted 2,2'-bipyridine ligands. Synthetic control of excited-state properties of ruthenium(II) tris-chelate complexes

Abstract

The synthesis of the novel bidentate ligands 4,4'-bis(trifluoromethyl)-2,2'-bipyridine (4,4'-BTFMB), 5,5'-bis-(trifluoromethyl)-2,2'-bipyridine (5,5'-BTFMB), and 4,4',5,5'-tetrakis(trifluoromethyl)-2,2'-bipyridine (4,4',5,5'-TTFMB) is reported. The photophysical and photochemical properties of a series of tris-chelate complexes [Ru(bpy)"(BTFMB)3-n]2+ ( = 0-2; bpy = 2,2'-bipyridine) are described. From spectroscopic and electrochemical measurements, it has been shown that the BTFMB ligand has lower lying ir* levels which not only lead to significant changes in ground-and excited-state redox potentials but also exert relatively large effects on absorption and emission spectral properties. From measurements of emission lifetime and quantum yield at room temperature, the radiative (kr) and nonradiative (knr) decay rate constants were obtained. Trends in k", properties are understandable on the basis of the energy gap law. Possible applications in excited-state redox chemistry are also discussed.

Static and Time-Resolved Spectroscopic Studies of Low-Symmetry Ru(II) Polypyridyl Complexes

“…1,11 However, a comparable change in absorption and emission energies has been documented in a series containing CF 3 -substituted bipyridines. 13 In this case, the dramatic shift was attributed to the introduction of a low-lying π* level residing on the CF 3 ligand, thus leading to localization of the 3 MLCT state on the CF 3 -containing ligand in mixedligand complexes. As shown by the preceding discussions, such is not the case in our system, despite the indication of the absorption spectral trend.…”

Proton-Induced Tuning of Electrochemical and Photophysical Properties in Mononuclear and Dinuclear Ruthenium Complexes Containing 2,2‘-Bis(benzimidazol-2-yl)-4,4‘-bipyridine: Synthesis, Molecular Structure, and Mixed-Valence State and Excited-State Properties

“…Three reversible one-electron reduction processes for [(btfmb) 2 Ru(bbbpyH 2 )Ru(btfmb) 2 ] 4+ were observed at -1.30, -1.52, and -1.91 V. However, the assignment of the reduction processes is not straightforward since the btfmb ligand has its π* orbitals at lower energy. 25 Deprotonation of the bbbpyH 2 ligand does not affect these reduction potentials. Both btfmb and bbbpyH 2 reduction waves may be overlapping.…”

Photoinduced Electron Transfer in Linear Triarylamine–Photosensitizer–Anthraquinone Triads with Ruthenium(II), Osmium(II), and Iridium(III)

“…[38][39]52 Three bpy-localized reductions of the metal complex occur between -1.72 and -2.15 V vs. Fc + /Fc, also in agreement with literature values. [53][54] Although these are clearly ligandcentered reductions, for convenience we will later designate the first of these reduction processes as a reduction of the ruthenium(II) complex to a ruthenium(I) species (Ru II /Ru I ). Oxidation of the TAA unit occurs at 0.30 V vs. Fc + /Fc, reduction of AQ is at -1.27 V vs. Fc + /Fc, both in agreement with previously reported redox potentials for these moieties.…”