Ground- and excited-state properties of a photostable hemicage ruthenium(II) polypyridine complex

Self-Photosensitizing Dinuclear Ruthenium Catalyst for CO2 Reduction to CO

The promise of artificial photosynthesis to solve environmental and energy issues such as global warming and the depletion of fossil fuels has inspired intensive research into photocatalytic systems for CO2 reduction to produce value-added chemicals such as CO and CH3OH. Among the photocatalytic systems for CO2 reduction, self-photosensitizing catalysts, bearing the functions of both photosensitization and catalysis, have attracted considerable attention recently, as such catalysts do not depend on the efficiency of electron transfer from the photosensitizer to the catalyst. Here, we have synthesized and characterized a dinuclear RuII complex bearing two molecules of a tripodal hexadentate ligand as chelating and linking ligands by X-ray crystallography to establish the structure explicitly and have used various spectroscopic and electrochemical methods to elucidate the photoredox characteristics. The dinuclear complex has been revealed to act as a self-photosensitizing catalyst, which acts not only as a photosensitizer but also as a catalyst for CO2 reduction. The dinuclear RuII complex is highly durable and performs efficient and selective CO2 reduction to produce CO with a turnover number of 2400 for 26 h. The quantum yield of the CO formation is also very high─19.7%─and the catalysis is efficient, even at a low concentration (∼1.5%) of CO2.

Synthesis and Characterization of Ferrocene Based Hemicages

We present a series of tripodal ligands L1-3, which fold into hemicages C1-3 by using coordination-driven dynamic combinational chemistry. The identities of these hemicages were characterized using ¹H NMR, ¹H-¹H COSY, DOSY, and ESI-TWIM-MS. Free rotation of the ferrocene structural units in the ligands affords an adaptable directionality, which is essential for the construction of these hemicages. Encapsulation of adamantane by C2 indicates the presence of a well-defined inner cavity as the binding pocket.

Supramolecular Hemicage Cobalt Mediators for Dye-Sensitized Solar Cells

A new class of dye-sensitized solar cells (DSSCs) using the hemicage cobalt-based mediator [Co(ttb)]2+/3+ with the highly preorganized hexadentate ligand 5,5'',5''''-((2,4,6-triethyl benzene-1,3,5-triyl)tris(ethane-2,1-diyl))tri-2,2'-bipyridine (ttb) has been fully investigated. The performances of DSSCs sensitized with organic D-π-A dyes utilizing either [Co(ttb)]2+/3+ or the conventional [Co(bpy)3 ]2+/3+ (bpy=2,2'-bipyridine) redox mediator are comparable under 1000 W m-2 AM 1.5 G illumination. However, the hemicage complexes exhibit exceptional stability under thermal and light stress. In particular, a 120-hour continuous light illumination stability test for DSSCs using [Co(ttb)]2+/3+ resulted in a 10 % increase in the performance, whereas a 40 % decrease in performance was found for [Co(bpy)3 ]2+/3+ electrolyte-based DSSCs under the same conditions. These results demonstrate the great promise of [Co(ttb)]2+/3+ complexes as redox mediators for efficient, cost-effective, large-scale DSSC devices.

Highly phosphorescent platinum(ii) emitters: photophysics, materials and biological applications

The structural effects of ligands on the emission properties of Pt(ii) complexes and promising applications of luminescent Pt(ii) complexes in various areas are discussed.

In recent years a blossoming interest in the synthesis, photophysics and application of phosphorescent Pt(ii) complexes, particularly on their uses in bioimaging, photocatalysis and phosphorescent organic light-emitting diodes (OLEDs), has been witnessed. The superior performance of phosphorescent Pt(ii) complexes in these applications is linked to their diverse spectroscopic and photophysical properties, which can be systematically modulated by appropriate choices of auxiliary ligands. Meanwhile, an important criterion for the practical application of phosphorescent metal complexes is their stability which is crucial for biological utilization and industrial OLED applications. Taking both the luminescence properties and stability into consideration, chelating ligands having rigid scaffolds and with strong σ-donor atoms are advantageous for the construction of highly robust phosphorescent Pt(ii) complexes. The square-planar coordination geometry endows Pt(ii) complexes with the intriguing spectroscopic and photophysical properties associated with their intermolecular interactions in both the ground and excited states. In this article, we discuss the design and synthesis of phosphorescent Pt(ii) complexes with elaboration on the effects of ligands on the structure and luminescence properties. Based on their photophysical and emission properties, we intend to shed light on the great promise of highly robust phosphorescent Pt(ii) emitters in an array of applications from molecular materials to biosensors.

Coordination mode dependent excited state behavior in group 8 phosphino(terthiophene) complexes

The ground and excited state behavior of four Ru(II) and Os(II) bipyridyl complexes containing the 3'-(diphenylphosphino)-2,2':5',2''-terthiophene (PT(3)) ligand in two different coordination modes (P,S and P,C) is reported. The complexes are generally stable under extended photoirradiation, except for [Ru(bpy)(2)PT(3)-P,S](PF(6))(2) which decomposes. Emission lifetimes and transient absorption spectra and lifetimes have been obtained for all the complexes. These data support a PT(3) ligand based lowest excited state in the case of both P,S bound complexes, and a charge separated lowest excited state in both P,C bound complexes, conclusions supported by Density Functional Theory (DFT) calculations.

Controlling the Helicity of 2,2‘-Bipyridyl Ruthenium(II) and Zinc(II) Hemicage Complexes

Two enantiomers of a new 4,5-pineno-2,2'-bipyridine ligand were synthesized and subsequently incorporated into hemicage ligands through a phenyl linker to yield ligands (+)-L1 and (-)-L1 or through a mesityl linker to yield ligands (+)-L2 and (-)-L2. Complexation of these ligands to Ru(II) afforded diastereomerically pure Delta and Lambda isomers, as verified through circular dichroism and circularly polarized luminescence spectroscopy. Ligands (+)-L2 and (-)-L2 were further coordinated to Zn(II) to form a complex with intriguing photophysical properties. Whereas Zn(bpy)32+ was shown to be a fluorescent emitter outside the visible spectrum, the caging process provided an unprecedented enhancement of intersystem crossing and subsequent switching to the phosphorescent emission of blue light. Additionally, the chiroptical properties of the Zn(II) complexes were also studied.

Synthesis, Characterization, and Photochemical/Photophysical Properties of Ruthenium(II) Complexes with Hexadentate Bipyridine and Phenanthroline Ligands

Three hexadentate, podand-type, polypyridyl ligands, (5-bpy-2C)(3)Bz, (4-bpy-2C-Ph)(3)Et, and (4-phen-2C-Ph)(3)Et, and their Ru(II) and Fe(II) complexes have been prepared. Reaction of these ligands with Fe(II) produces only the monometallic hemicage species, while monometallic, bimetallic, and polymetallic Ru(II) complexes are formed. These species are separable by column chromatography, and NMR and ESI mass spectrometry demonstrate that with each ligand the first band to elute corresponds to the monometallic species, [RuL](2+). The ESI mass spectra show peaks for [RuL](2+) and [RuL](PF(6))(+) with expected m/z values and isotope peak spacings. (1)H NMR spectroscopy shows that [Ru(5-bpy-2C)(3)Bz](2+) is trigonally symmetric and contains a rigid methylene bridge between the capping group and the bipyridines. The excited-state lifetimes and emission quantum yields for the hemicage complexes, [Ru(5-bpy-2C)(3)Bz](2+), [Ru(4-bpy-2C-Ph)(3)Et](2+), and [Ru(4-phen-2C-Ph)(3)Et](2+), are significantly enhanced (tau = 2800, 1470, and 3860 ns, and Phi(em) = 0.271, 0.104, 0.202, respectively) relative to the model compounds and to the polymetallic complexes with the same ligand. An Arrhenius fit of temperature-dependent lifetime data for [Ru(5-bpy-2C)(3)Bz](2+) indicates a high activation energy for crossover to the dd state (DeltaE = 4960 cm(-)(1)) as well as the existence of an additional pathway for deactivation via a "4th MLCT" state. Only after extensive photolysis of [Ru(5-bpy-2C)(3)Bz](2+) is any decrease in emission intensity observed; this is accompanied by the formation of a bimetallic photoproduct, [Ru(2)L(2)](4+), with a quantum yield of 7.4 x 10(-)(6). Quenching studies with a variety of quenchers show that the useful excited-state redox and energy-transfer properties characteristic of Ru(II) polypyridyls are retained, but with improved photoinertness and photophysical properties arising from the rigidity of the hemicage complex.

Large Clusters of Metal Ions: The Transition from Molecular to Bulk Magnets

Clusters of metal ions are a class of compounds actively investigated for their magnetic properties, which should gradually change from those of simple paramagnets to those of bulk magnets. However, their interest lies in a number of different disciplines: chemistry, which seeks new synthetic strategies to make larger and larger clusters in a controlled manner; physics, which can test the validity of quantum mechanical approaches at the nanometer scale; and biology, which can use them as models of biomineralization of magnetic particles.