Si-Hai Wu

Transition from a Metal-Localized Mixed-Valence Compound to a Fully Delocalized and Bridge-Biased Electrophore in a Ruthenium-Amine-Ruthenium Tricenter System.

A series of cyclometalated diruthenium complexes with a redox-active amine bridge were synthesized. Depending on the terminal ligands of the ruthenium components and the substituent on the amine unit, the one-electron-oxidized state can be either in the form of a weakly or strongly coupled mixed-valence diruthenium complex, a fully charge-delocalized three-center system, or a bridge-biased electrophore. This transition among different electronic forms was supported by electrochemistry, near-infrared absorption, electron paramagnetic resonance, and density functional theory analysis.

Cyclometalated ruthenium oligomers with 2,3-di(2-pyridyl)-5,6-diphenylpyrazine: a combined experimental, computational, and comparison study with noncyclometalated analogous.

Recent investigations on polypyridine transition-metal complexes as potential molecular wires have provided new impetus for these long-studied and well-established systems. Using bridging ligands 2,3-di(2-pyridyl)-5,6-diphenylpyrazine (dpdpz) and 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz), a tetrametallic cyclometalated ruthenium complex has been prepared and characterized, with each metal having one Ru-C bond. The electronic properties of this complex and two known monoruthenium and diruthenium complexes with dpdpz (DPDPZ series) were probed by electrochemical and spectroscopic techniques and compared to the previously reported tppz-based noncyclometalated ruthenium complexes (TPPZ series). The frontier orbital energy levels and electronic structures of the two series have been characterized by density functional theory (DFT) calculations. In accordance with the experimental results, these studies suggest that the DPDPZ series oligomers generally have a narrower energy gap relative to the TPPZ series. In addition, the large energy density of states in longer oligomers suggests the possibility of band-type conduction. The DPDPZ series exhibits red-shifted light absorption with enhanced intensity relative to the TPPZ series congeners. Time-dependent DFT computations have been performed to rationalize the electronic absorption of the DPDPZ series. Oxidative spectroelectrochemical measurements of the DPDPZ tetrametallic complex indicate the presence of intervalence charge-transfer transitions among ruthenium sites.