PHOTOPHYSICS OF RUTHENIUM(II) COMPLEXES WITH 2-(2'-PYRIDYL)PYRIMIDINEAND 2,2'-BIPYRIDINE LIGANDS IN FLUID SOLUTION

The photophysics of three complexes of the form Ru(bpy)(3-p)(pypm)(p)( 2+) (where bpy=2,2'-bipyridine, pypm=2-(2'-pyridyl)pyrimidine and p=1, 2 or 3) was examined in H2O, propylene carbonate, CH2CN and 4 : 1 (v/ v) C2H5OH-CH3OH; comparison was made with the well-known photophysical behavior of Ru(bpy)(3)(2+). The lifetimes of the luminescent metal-to -ligand charge transfer (MLCT) excited states were determined as a fun ction of temperature (between -103 and 90 degrees C, depending on the solvent), from which were extracted the rate constants for radiative a nd non-radiative decay and Delta E, the energy gap between the MLCT an d metal-centered (MC) excited states. The results indicate that Ru(bp y)(2)(pypm)(2+) decays via a higher lying MLCT state, whereas Ru(pypm )(3)(2+) and Ru(pypm)(2)(bpy)(2+) decay predominantly via the MC stat e. (C) 1997 Elsevier Science S.A.