Synthesis and Molecular Design of Ruthenium Polynuclear Complexes Responding Logically to Trigger Signals

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We are focusing on the molecular design of the Ru polynuclear complexes which can respond logicaly to the trigger signal such proton movements. The summary of this project during the term is the following :(1) Synthesis of Ru di- and tetranuclear complexes bridged by organice benzimidazole. We have developed the chemical principle underlying the proton-induced switching of redox potential, i.e., reversible protonation of uncoordinated nitrogen site in 2- (2-pyridyl) benzimidazole Ru di- and tetranuclear complexes. In heteronuclear Ru-Rh dinuclear complex, the emission was observed at the deprotonated state of Rh site, however when the protonation occurred at Rh site, no emission was observed. Thus, the emission switching was observed in this dinuclea complex. We are extending this chemistry to the dendrimer type tetranuclear complexes. Two oxidation patterns have been reported in ligand-bridged dendrimer tetranuclear complexes when the four metal ions are connected by bridging ligands … More in the star-burst like manner and each metal-metal interaction is weak. Pattern A consists in simultaneous oxidation of three peripheral metals at almost same potentials prior to one-electron oxidation of the central metal ion. The second pattern B is the reverse. In the present RuOs mixed metal tetranuclear complex, [ {Os (bpy)_2 (bbbpyH_2) }_3 Ru] (CIO_4)_8 (bpy=2,2'-bipyridine) , the two redox patterns A and B can be interchanged by protonation of basic sites. Within the one-electron oxidized form of the deprotonated complex 2^+ (Ru^<III>Os^<II>_3) , the electron transfer from peripheral Os^<II> to central Ru^<III> moiety has occurred on protonation.(2) Formation of photoinduced charge separated state in RuOs Complex : The picosecond laser flash photolysis of dinuclear Ru (II) -NDI-Os (III) complex shows that the bleaching of MLCT band and then the appearance of new bands at 650 nm were observed. These new bands corresponds to the fprmation of Ru (III) -NDI-Os (II) state. The stepwise photoinduced electron transfer from the Ru (bpy) moiety to the dicarboximide, and then Os (III) occurred.(3) We showed that electrospray ionization mass spectra is a powerful tool for the characterization and purity check of tetranuclear Ru complexes. Less