Synthesis and Photophysical Properties of 3,8-Disubstituted 1,10-Phenanthrolines and Their Ruthenium(II) Complexes

The palladium-catalysed cross-coupling reaction between 3,8-dibromo-1, 10-phenanthroline with phenylacetylene or 3,5-bis(trifluoromethyl)phenylboronic acid gives good yields of the 3,8-disubstituted products. These 1,10-phenanthroline derivatives are used for the formation of novel ruthenium complexes of the type [(tbbpy)(2)Ru(phenR(2))(2+) [where tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine, phen = 1,10-phenanthroline, R represents the substituents at the 3,8 positions with bromine, phenylacetylene or 3,5-bis(trifluoromethyl)phenyl]. All compounds are completely characterised by NMR and UV/Vis spectroscopy, MS, electrochemical measurements and Raman and resonance Raman spectroscopy. The photophysical properties indicate a strong influece of the substitution of the phenanthroline ligand on the absorption and Raman properties. With resonance Raman spectroscopy the localisation of the singlet metal-to-ligand charge-transfer ((MLCT)-M-1) excited state is determined. The solid-state structures of 3,8-dibromo-1,10-phenanthroline (phenBr(2)) and the corresponding ruthenium complex [(tbbpy)(2)-Ru(phenBr2)](2+) and a structural motif of [(tbbpy)(2)-Ru{phen-3,8-bis(trifluoromethyl)phenyl]}](2+) are also reported. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)