A COMBINED SPECTROSCOPIC, PHOTOPHYSICAL AND THEORETICAL (DFT) STUDY OF THE ELECTRONICALLY EXCITED INORGANOMETALLIC COMPLEXES [RU(E)(E')(CO)(2)(IPR-DAB)] (E=CL, ME, SNPH(3), PBPH(3) E'=GEPH(3), SNR(3), PBR(3), (R=ME, PH), IPR-DAB=N,N'-DIISOPROPYL-1,4-DIAZA-1,3-BUTADIENE) - EVIDENCE OF AN EXCEPTIONALLY LONG-LIVED (3)SIGMA-PI-ASTERISK EXCITED-STATE FOR [RU(SNPH(3))(2)(CO)(2)(IPR-DAB)]

The photophysical properties of the metal-metal bonded complexes [Ru(E )(E')(CO)(2)(iPr-DAB)] (E = Cl, E' = SnPh(3), PbPh(3); E = Me, E' = Sn Ph(3), PbPh(3); E = SnPh(3), E' = SnMe(3), SnPh(3), GePh(3); E = PbPh( 3), E' = PbMe(3), PbPh(3). GePh(3); iPr-DAB = N,N'-diisopropyl-1,4-dia za-1,3-butadiene) have been studied. According to time-resolved emissi on, UV/vis and IR spectra, combined with density functional (DFT) MO c alculations. the lowest excited state has triplet metal-to-ligand char ge-transfer ((3)MLCT). triplet halide-to-ligand charge-transfer ((3)XL CT) or (3) sigma((E-Ru-E'))pi character, depending pending on the nat ure and combination of the ligands E and E'. The (3) sigma((E-Ru-E'))p i state is a bound state whose lifetime is strongly influenced by the ligands E and E'. An exceptionally long lifetime (264 mu s at 80 K) i s observed for the (3) sigma((Sn-Ru-Sn))pi state of the symmetrically substituted [Ru(SnPh(3))(2)(CO)(2)(iPr-DAB)] complex. The reason for this long lifetime is the fact that the excited state of this complex is hardly distorted with respect to the ground state, owing to the del ocalised character of the sigma(Sn-Ru-Sn) bonding orbital, which mixes strongly with the pi orbital of the iPr-DAB ligand. This delocalisat ion is also responsible for the unusually high oscillator strength of the sigma --> pi electronic transition in the visible spectral region .