TRIFLUOROMETHYL-SUBSTITUTED 2,2'-BIPYRIDINE LIGANDS - SYNTHETIC CONTROL OF EXCITED-STATE PROPERTIES OF RUTHENIUM(II) TRIS-CHELATE COMPLEXES

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)n(BTFMB)3-n]2+ (n = 0-2; bpy = 2,2'-bipyridine) are described. From spectroscopic and electrochemical measurements, it has been shown that the BTFMB ligand has lower lying pi* 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 (k(r)) and nonradiative (k(nr)) decay rate constants were obtained. Trends in k(nr) properties are understandable on the basis of the energy gap law. Possible applications in excited-state redox chemistry are also discussed.