Syntheses and Electrochemical, Photophysical, and Photochemical Properties of Ruthenium(II) 4,5-Diazafluorenone Complexes and Their Ketal Derivatives

Abstract

A series of ruthenium(II) complexes of the types [Ru(bpy)n(dafo)3-n]2+ and [Ru(bpy)n(dafo-ketal)3-n]2+, where n varies between 0 and 3 and dafo is 4,5-diazafluoren-9-one, were synthesized, and their chemical, physical, and photophysical properties were examined. The coordinated dafo-ketal ligand readily forms by the direct reaction of [Ru(bpy)n(dafo)3-n]2+ complexes with ethylene glycol or by reaction of the appropriate ruthenium precursors with the correct stoichiometric amount of the dafo ligand in ethylene glycol. In each series, the visible absorption band associated with the MLCT transition shifts to the blue and the electrochemical oxidation associated with the Ru(III)/Ru(II) couple becomes more positive as n decreases. Coordinated dafo undergoes a one-electron reduction at potentials <−1 V and a second one-electron reduction at ∼−1.2 V vs SSCE. The first reduction can be associated with reduction of the carbonyl group; the second, with reduction of the bipyridine portion. Coordinated dafo-ketal onl...