Photophysics of ruthenium(II) complexes with 2-(2′-pyridyl)pyrimidine and 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 function of temperature (between -103 and 90 degrees C, depending on the solvent), from which were extracted the rate constants for radiative and non-radiative decay and Delta E, the energy gap between the MLCT and metal-centered (MC) excited states. The results indicate that *Ru(bpy)(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 state. (C) 1997 Elsevier Science S.A.