NEW CHARGE-TRANSFER LUMINESCENT POLYMETALLIC COMPLEXES OF RHODIUM(III), IRIDIUM(III), AND RUTHENIUM(II) WITH THE BRIDGING LIGAND 1,4,5,8,9,12-HEXAAZATRIPHENYLENE

New emitting binuclear (Rh)(i)-(Ru)(2-i) (i = 1, 2), (Ir)-(Ru), and trinuclear (Rh)(i)-(Ru)(3-i) (i = 1, 2, 3) complexes assembled by the trischelating bridging ligand HAT (1,4,5,8,9,12-hexaazatriphenylene), have been synthesized. Their characterization by mass spectrometry (FAB and electrospray) is in accordance with their expected structure, where Rh(PPY)(2)(+) (or Ir(PPY)(2)(+)) and Ru(BPY)(2)(2+) correspond to the building blocks (PPY is the ortho-C-deprotonated form of 2-phenylpyridine and BPY is 2,2'-bipyridine). The HPLC data of these polymetallic compounds reveal that the trimetallic homo- and heteronuclear complexes are not stable under the chromatographic conditions and in some organic solvents. Therefore, the electrochemical and photophysical data are given only for the bimetallic compounds, stable under these conditions. Under electrochemical oxidation, the bimetallic Rh(III) complex shows one irreversible wave in the accessible potential range, while the heteronuclear Rh(III)-Ru(II) and Ir(III)-Ru(II) compounds exhibit an irreversible process followed by a reversible wave. For the bimetallic (homo- and heteronuclear) complexes, the first reduction wave involves a HAT-centered pi* orbital. On the basis of the electrochemical, luminescence and resonance Raman data, the lowest electronic transitions are CT (charge transfer) transitions involving the bridging HAT. These transitions have an MLCT (metal to ligand charge transfer) type for the Ru(II) moiety and a SBLCT (sigma-bond to ligand charge transfer) character for the Rh(III) unit; in the case of the Ir(III) moiety there is a strong admixture of SBLCT and MLCT character. An energy transfer would take place from the Ru-HAT (3)MLCT state towards the Ir-HAT (3)SBLCT (mixed with (3)MLCT character) in the Ir(III)-Ru(II) compound. For the Rh(III)-Ru(II) complex the nature of the luminescent excited state (Ru-HAT (3)MLCT or Rh-HAT (3)SBLCT) cannot be unambiguously determined.