Diamines as auxiliary ligands for tuning photophysical and electrochemical properties of Ruthenium(II) polypyridyl complexes

The complex with the formula [Ru(bpy)(2)(2,3-diaminonaphthalene)1[PF6] (5) was synthesized and characterized by H-1 NMR spectroscopy, mass spectrometry and elemental analysis. A set of previously reported complexes with the formula [Ru(bpy)(2)(diamine)][PF6]{diamine = 1,2-diaminoethane (2), o-phenylenediamine (3), 1,2-diaminocyclohexane (4) I was synthesized and crystal structures were obtained for complexes 3 and 4. UV vis absorption spectra of the complexes 2-5 were collected and compared to that of [Ru(bPY)(3)][PF6](2) (1), showing that the MLCT band is red-shifted upon introducing the diamine ligands in place of bipyridine. Emission spectra, excited-state lifetimes and emission quantum yields were collected at room temperature for the complexes 1-5, showing considerable changes in the photophysical characteristics upon the introductions of the diamine. The emission spectrum of 5 exhibits an intense emission in the far red-NIR region when excited at 510 nm. The cyclic voltammograms of the complexes 1-5 show one oxidation peak between 0.98 V and 1.15 V which is attributed to the Ru(II)/Ru(III) oxidation couple. Calculated HOMO and LUMO energy levels from both electrochemical data and theoretical calculations suggest a lower HOMO energy level for complex 1 than the diamino-containing complexes, presumably due to the stronger ligand field of the bipyridine. (C) 2018 Elsevier B.V. All rights reserved.