Synthesis and Molecular-assembling of Metal Polynuclear Complexes as a Switching Molecular Devices by Proton Transfer

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In the Ru complexes containing the proton dissociable LH, the thermodynamic relations between electron transfer, proton transfer and photoexcitation can be summarized by a three-dimensional cubic scheme(Fig.1). In this scheme, the thermodynamic quantities such as pK_a and redox potential E_<1/2> are correlated each other. This thermodynamic scheme inspires us to design the supramolecular complexes which can possess a proton-induced switching activity. The proton dissociation in Ru complexes leads to the changes of redox potentials and donor poperty of the ligand, which induces the switching of redox and photochemical properties in the complexes. To elucidate this phenomenon, new dinuclear Ru complexes containing proton dissociable benzimidazole derivatives have been prepared. As a bridging ligand, several new ligands were introduced ; i.e., 2,2'-bis(2-benzimidazolyl)-4,4'-bipyridine(bbbpyH_2) and 2,2'-bis(2-pyridyl)-bibenzimidazole(bpbimH_2). A series of mono-, di-, tri-and tetranuclear Ru complexes bridged by these benzimidazole derivatives have been synthezized. Proton transfer in these complexes can functionas an external perturbation for (1) the change of the metal-metal interaction through bnridging ligand ; (2) the change of the localized position for the excited electron ; (3) the change of the pathway for the electron transfer ; (4) the change of the multielectron transfer pocesses ; for example, the change from the two-electron process to two one-electron processes. The complexes exhibit different switching modes on the redox behaviors, emission, or metal-metal interaction.