SYNTHESIS AND CHARACTERIZATION OF A MULTIBRIDGED PORPHYRIN COMPLEX CONTAINING PERIPHERAL BIS(BIPYRIDINE)-RUTHENIUM(II) GROUPS

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Abstract
The synthesis and characterization of a new meso-tetrapyridylporphyrin (TPyP) modified with four [Ru(bipy)2Cl]+ groups is reported. Cyclic voltammograms of this species in N,N′-dimethylformamide exhibit three reversible waves at 0.92, −0.68 and −0.93 V versus SHE, ascribed to the ruthenium(III/II) redox couple, and to successive monoelectronic redox processes at the porphyrin ring. Electronic spectra show the characteristic Soret band at 418 nm and the β, α doublets of the porphyrin at 518, 558; and 594, 650 nm, respectively, in addition to the absorption bands of the [Ru(bipy)2(pyP)Cl] groups at 298 nm (bipy φ*), 470 nm (RuII→bipy charge-transfer) and 368 nm (ligand field transition). The complex emits around 655 nm, when excited at the porphyrin or Ru(bipy)2Cl+ absorption bands. The diprotonated species [H2TPyP{RuII(bipy)2Cl}4] displays a new intense band at 690 nm which disappears when the metal ions are oxidized, or when the porphyrin is reduced, suggesting a ruthenium(II)-to-protonated porphyrin charge-transfer transition.