The goal of artificial photosynthesis is to use the energy of the sun to make high-energy chemicals for energy production. One approach, described here, is to use light absorption and excited-state electron transfer to create oxidative and reductive equivalents for driving relevant fuel-forming half-reactions such as the oxidation of water to O2 and its reduction to H2. In this "integrated modular assembly" approach, separate components for light absorption, energy transfer, and long-range electron transfer by use of free-energy gradients are integrated with oxidative and reductive catalysts into single molecular assemblies or on separate electrodes in photelectrochemical cells. Derivatized porphyrins and metalloporphyrins and metal polypyridyl complexes have been most commonly used in these assemblies, with the latter the focus of the current account. The underlying physical principles--light absorption, energy transfer, radiative and nonradiative excited-state decay, electron transfer, proton-coupled electron transfer, and catalysis--are outlined with an eye toward their roles in molecular assemblies for energy conversion. Synthetic approaches based on sequential covalent bond formation, derivatization of preformed polymers, and stepwise polypeptide synthesis have been used to prepare molecular assemblies. A higher level hierarchial "assembly of assemblies" strategy is required for a working device, and progress has been made for metal polypyridyl complex assemblies based on sol-gels, electropolymerized thin films, and chemical adsorption to thin films of metal oxide nanoparticles.

Chemical approaches to artificial photosynthesis. 2.

Coordination complexes have been used extensively as the photoactive component of artificial photosynthetic devices. While polynuclear arrays increase the probability of light absorption, the incorporation of the stereogenic Ru(2,2′-bipyridine)32+ motif gives rise to diastereomeric mixtures whereas the achiral Ru(2,2′:6′,2″-terpyridine)22+ motif creates stereopure polynuclear complexes. Thus, polynuclear arrays composed of ruthenium(II) complexes of tridentate ligands are the targets of choice for light-harvesting devices. As Ru(II) complexes of tridentate ligands have short excited state lifetimes at room temperature (r. t.), considerable effort has been focused on trying to increase their r. t. luminescence lifetime for practical applications. This tutorial review will report on the sophisticated synthetic strategies currently in use to enhance the room temperature photophysical properties of Ru(II) complexes of tridentate ligands.

Designing tridentate ligands for ruthenium(II) complexes with prolonged room temperature luminescence lifetimes

Aromatic nitrogen heterocycles as bridging ligands; a survey

Electrochemical studies of ruthenium compounds part I. Ligand oxidation levels

The role of autophagy in cancer development and response to cancer therapy has been a subject of debate. Here we demonstrate that a series of ruthenium(II) complexes containing a β-carboline alkaloid as ligand can simultaneously induce autophagy and apoptosis in tumor cells. These Ru(II) complexes are nuclear permeable and highly active against a panel of human cancer cell lines, with complex 3 displaying activities greater than those of cisplatin. The antiproliferative potentialities of 1−3 are in accordance with their relative lipophilicities, cell membrane penetration abilities, and in vitro DNA binding affinities. Complexes 1−3 trigger release of reactive oxygen species (ROS) and attenuation of ROS by scavengers reduced the sub-G1 population, suggesting ROS-dependent apoptosis. Inhibition of ROS generation also reduces autophagy, indicating that ROS triggers autophagy. Further studies show that suppression of autophagy using pharmacological inhibitors (3-methyladenine and chloroquine) enhances apoptot...

Nuclear Permeable Ruthenium(II) β-Carboline Complexes Induce Autophagy To Antagonize Mitochondrial-Mediated Apoptosis

The synthesis, structure, and redox and photophysical properties of (Ru(bpy)/sub n/(BL)/sub 3-n/)/sup 2 +/, where n = 0-2, bpy is 2,2'-bipyridine, and BL is 2,3-bis(2-pyridyl)quinoxaline, are described. The (Ru(bpy)/sub 2/(BL))(PF/sub 6/)/sub 2/ complex crystallized in the monoclinic space group P2/sub 1//a and the cell parameters are repeated. All non-H atoms were refined anisotropically to an R value of 0.0672 for 5766 reflections with I > sigma(I). The ruthenium to nitrogen bond distances were Ru-N(pyridine) = 2.06 A (average) and Ru-N(pyrazine) = 2.096 (4) A. Absorption spectra contained bands (250-300 nm) in the ultraviolet region that were assignable to ligand ..pi.. ..-->.. ..pi..* transitions and visible bands (517-300 nm) that were assignable to d..pi.. ..-->.. ..pi..* MLCT transitions. Reduction potentials for the Ru/sup 3+/2+/ couples varied from about 1.40 to 1.70 V vs SSCE. Three reductions were observed and assigned to the one-electron reduction of each bidentate ligand. Weak luminescence was observed, and corrected emission energy maxima were located at 766 +/- 4 nm. Excited-state reduction potentials were estimated from the difference between emission energy maxima and ground-state reduction potentials. Excited-state lifetimes at room temperature in 4:1 EtOH-MeOH ranged from 167 to < 70 ns. Temperature-dependent-lifetime (90-298 K) data gave evidencemore » for ..delta..E' values of 1100 +/- 300 cm/sup -1/. The temperature dependence was attributed to either the third MLCT state according to the localized-orbital model or the presence of a fourth CT state for (Ru(BL)/sub 2/(bpy))/sup 2 +/, since little photochemistry was found for it, and to the third and/or the fourth CT state and the dd state for both (Ru(BL)/sub 2/(bpy))/sup 2 +/ and (Ru(BL)/sub 3/)/sup 2 +/. 54 references, 7 figures, 6 tables.« less

Structure and redox and photophysical properties of a series of ruthenium heterocycles based on the ligand 2,3-bis(2-pyridyl)quinoxaline

The structures of [Ru(bpy)[sub 3]](PF[sub 6])[sub 2] (bpy = 2,2[prime]-bipyridine) and [Ru(bpm)[sub 3]](PF[sub 6])[sub 2][center dot]CH[sub 3]CN (bpm = 2,2[prime]-bipyrimidine) have been determined by single-crystal X-ray diffraction. [Ru(bpy)[sub 3]](PF[sub 6])[sub 2] crystallized in the hexagonal space group. [Ru(bpm)[sub 3]](PF[sub 6])[sub 2][center dot]CH[sub 3]CN crystallized in the triclinic space group. Ru-N bond distances in [Ru(bpy)[sub 3]][sup 2+] were 2.056 (2) [angstrom] and average 2.067 (4) [angstrom] in [Ru(bpm)[sub 3]][sup 2+]. Other bond distances and angles lead to the conclusion that the structures of the [Ru(bpy)[sub 3]][sup 2+] and [Ru(bpm)[sub 3]][sup 2+] cations are basically the same.

H. A. Levy

Papers

Structure and redox and photophysical properties of a series of ruthenium heterocycles based on the ligand 2,3-bis(2-pyridyl)quinoxaline

Comparison of the crystal structures of tris heterocyclic ligand complexes of ruthenium(II)

Structure and Redox and Photophysical Properties of a Series of Ruthenium Heterocycles Based on the Ligand 2,3-Bis(2-pyridyl)quinoxaline.