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)2Ru(phenR2)]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 influence of the substitution of the phenanthroline ligand on the absorption, emission and Raman properties. With resonance Raman spectroscopy the localisation of the singlet metal-to-ligand charge-transfer (1MLCT) excited state is determined. Thesolid-state structures of 3,8-dibromo-1,10-phenanthroline (phenBr2) and the corresponding ruthenium complex [(tbbpy)2Ru(phenBr2)]2+ and a structural motif of [(tbbpy)2Ru{phen-3,8-bis[3,5-bis(trifluoromethyl)phenyl]}]2+ are also reported.