Broad HOMO-LUMO gap tuning through the coordination of a single phosphine, aminophosphine or phosphite onto a Ru(tpy)(bpy)2+ core.

The synthesis of new ruthenium(II) terpyridine bipyridine complexes bearing a phosphorus(III) ligand is presented. The steric and electronic properties of the phosphorus ligand were varied using aminophosphines, alkyl and aryl phosphites and the bulky tri(isopropyl) phosphine. All complexes were characterized by multi-nuclear NMR spectroscopy, mass spectrometry and X-ray diffraction analysis. The electronic properties of the complexes were probed by cyclic voltammetry, absorption and luminescence spectroscopy. The complexes do not show luminescence at room temperature, whereas at 77 K in an alcoholic matrix, emission is observed in the range 600-650 nm with lifetimes of 3.5-5.5 mu s, originating from (MLCT)-M-3 states. The MLCT transition spans over 65 nm, which corresponds to a variation of 0.4 eV in the HOMO LUMO gap. The oxidation potential of the ruthenium varies over a broad range of 290 mV, from +1.32 V vs. SCE with L = (PPr3)-Pr-i to + 1.61 V vs. SCE with L = P(OPh)(3). This range is unprecedented upon the variation of a single monodentate ligand coordinated by the same heteroatom in the same oxidation and charge states. This work underlines the specific capacity of phosphorus in bringing up a large variety of electronic properties by changing its substituents.