New star-shaped trinuclear Ru(ii) polypyridine complexes of imidazo[4,5-f][1,10]phenanthroline derivatives: syntheses, characterization, photophysical and electrochemical properties

Abstract

A series of new star-shaped trinuclear Ru(II) complexes of imidazo[4,5-f][1,10]phenanthroline derivatives, [{Ru(bpy)₂}₃{μ-mes(1,4-phO-Izphen)₃}](ClO₄)₆·4H₂O (6), [{Ru(phen)₂}₃{μ-mes(1,4-phO-Izphen)₃}](ClO₄)₆·3H₂O (7), [{Ru(bpy)₂}₃{μ-mes(1,2-phO-Izphen)₃}](ClO₄)₆·4H₂O (8), and [{Ru(phen)₂}₃{μ-mes(1,2-phO-Izphen)₃}](ClO₄)₆·3H₂O (9) [mes(1,4-phO-Izphen)₃ (4) = 2,4,6-tri methyl-1,3,5-tris(4-oxymethyl-1-yl(1H-imidazo-2-yl-[4,5-f][1,10]phenanthroline)phenyl)benzene and (mes(1,2-phO-Izphen)₃ (5) = 2,4,6-trimethyl-1,3,5-tris(2-oxymethyl-1-yl(1H-imidazo-2-yl[4,5-f][1,10]phenanthroline)phenyl)benzene] have been synthesized and characterized. Their photophysical and electrochemical properties have also been studied. The core molecule, 1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene (1) and the trialdehyde intermediate, 2,4,6-trimethyl-1,3,5-tris(4-oxymethyl-1-formylphenyl)benzene (2) are characterized by single crystal X-ray diffraction: triclinic, P. The complexes 6–9 exhibit Ru(II) metal centered emission at 618, 601, 615, and 605 nm, respectively, in fluid solution at room temperature. The emission profile and emission maxima are similar and independent of the excitation wavelength for each complex. The complexes 6–9 undergo metal centered oxidation and the E_1/2 values for the Ru(II)/Ru(III) redox couples are 1.33, 1.34, 1.35, and 1.35 V versus Ag/Ag⁺, respectively, which are cathodically shifted with respect to that of the mononuclear complex [Ru(bpy)₂(PIP)]²⁺ (PIP = 2-phenylimidazo[4,5-f][1,10]phenanthroline). The study demonstrates the versatility of the highly symmetric trinucleating imidazo[4,5-f][1,10]phenanthroline-based core ligands 4 and 5 in forming trinuclear Ru(II) complexes.