HIGH-PRESSURE STUDIES OF PHOTOLUMINESCENCE PROPERTIES OF RUTHENIUM(II) POLYPYRIDYL COMPLEXES

The intensities, lifetimes, and peak locations for the luminescence of [Ru(bpy)2(py)2]2+ (bis) and [Ru(bpy)3]2+ (tris) complexes (bpy =- 2,2'-bipyridine; py = pyridine) have been measured as a function of pressure in three media: the crystalline solid, poly(4-vinylpyridine) (PVP), and poly(acrylic acid) (PAA). At atmospheric pressure the bis complex exhibited a weak emission which varied only slightly with the medium. For the tris complex the emission was much more intense and media dependent. It has been established that the emission is a 3MLCT transition ito an orbital localized primarily on the bpy. In addition to the radiative path (k(r)) there is a direct nonradiative path (k(nr)) as well as a thermal pathway via transfer to an excited ligand field state (k0' exp(-DELTAE/RT)). In all cases the pressure effects on the relative intensities and lifetimes match each other qualitatively very well. The tris emission intensity and lifetime decrease monotonically with increasing pressure, in proportion to the peak shift to lower energy, and thus primarily involve an increase in k(nr) caused by the decreasing energy gap. For the bis emission there is a strong intensity increase at lower pressures apparently involving a decrease in k(nr) due to inhibition of pyridine motion and at higher pressures a decrease essentially paralleling the behavior of the tris.