Photo-induced 6π-electrocyclisation and cycloreversion of isolated dithienylethene anions.

The diarylethene chromophore is commonly used in light-triggered molecular switches. The chromophore undergoes reversible 6π-electrocyclisation (ring closing) and cycloreversion (ring opening) reactions upon exposure to UV and visible light, respectively, providing bidirectional photoswitching. Here, we investigate the gas-phase photoisomerisation of - () and - () substituted dithienylethene carboxylate anions (DTE) using tandem ion mobility mass spectrometry coupled with laser excitation.

Post-Assembly Covalent Di- and Tetracapping of a Dinuclear [Fe2L3](4+) Triple Helicate and Two [Fe4L6](8+) Tetrahedra Using Sequential Reductive Aminations.

The use of a highly efficient reductive amination procedure for the postsynthetic end-capping of metal-templated helicate and tetrahedral supramolecular structures bearing terminal aldehyde groups is reported. Metal template formation of a [Fe2L3](4+) dinuclear helicate and two [Fe4L6](8+) tetrahedra (where L is a linear ligand incorporating two bipyridine domains separated by one or two 1,4-(2,5-dimethoxyaryl) linkers and terminated by salicylaldehyde functions is described. Postassembly reaction of each of these "open" di- and tetranuclear species with excess ammonium acetate (as a source of ammonia) and sodium cyanoborohydride results in a remarkable reaction sequence whereby the three aldehyde groups terminating each end of the helicate, or each of the four vertices of the respective tetrahedra, react with ammonia then undergo successive reductive amination to yield corresponding fully tertiary-amine capped cryptate and tetrahedral covalent cages.

Controlling ground and excited state properties through ligand changes in ruthenium polypyridyl complexes.

The capture and storage of solar energy requires chromophores that absorb light throughout the solar spectrum. We report here the synthesis, characterization, electrochemical, and photophysical properties of a series of Ru(II) polypyridyl complexes of the type [Ru(bpy)2(N-N)](2+) (bpy = 2,2'-bipyridine; N-N is a bidentate polypyridyl ligand). In this series, the nature of the N-N ligand was altered, either through increased conjugation or incorporation of noncoordinating heteroatoms, as a way to use ligand electronic properties to tune redox potentials, absorption spectra, emission spectra, and excited state energies and lifetimes.

Synthesis of phosphonic acid derivatized bipyridine ligands and their ruthenium complexes.

Water-stable, surface-bound chromophores, catalysts, and assemblies are an essential element in dye-sensitized photoelectrosynthesis cells for the generation of solar fuels by water splitting and CO2 reduction to CO, other oxygenates, or hydrocarbons. Phosphonic acid derivatives provide a basis for stable chemical binding on metal oxide surfaces. We report here the efficient synthesis of 4,4'-bis(diethylphosphonomethyl)-2,2'-bipyridine and 4,4'-bis(diethylphosphonate)-2,2'-bipyridine, as well as the mono-, bis-, and tris-substituted ruthenium complexes, [Ru(bpy)2(Pbpy)](2+), [Ru(bpy)(Pbpy)2](2+), [Ru(Pbpy)3](2+), [Ru(bpy)2(CPbpy)](2+), [Ru(bpy)(CPbpy)2](2+), and [Ru(CPbpy)3](2+) [bpy = 2,2'-bipyridine; Pbpy = 4,4'-bis(phosphonic acid)-2,2'-bipyridine; CPbpy = 4,4'-bis(methylphosphonic acid)-2,2'-bipyridine].

Electrogenerated polypyridyl ruthenium hydride and ligand activation for water reduction to hydrogen and acetone to iso-propanol.

The complex [Ru(tpy)(bpy)(S)](2+) (tpy = 2,2':6',2''-terpyridine, bpy = 2,2'-bipyridine, S = solvent) is an electrocatalyst for water or proton reduction to hydrogen and for reduction of acetone to iso-propanol in CH3CN. Electrocatalysis is initiated by sequential 1e(-) reductions at the tpy and bpy ligands followed by addition of water to give a ruthenium hydride intermediate. Significant rate enhancements for hydrogen evolution are observed with added weak acids, such as H2PO4(-), for the latter, with a rate enhancement of 10(4) compared to water.

Photoinduced electron transfer in a chromophore-catalyst assembly anchored to TiO2.

Photoinduced formation, separation, and buildup of multiple redox equivalents are an integral part of cycles for producing solar fuels in dye-sensitized photoelectrosynthesis cells (DSPECs). Excitation wavelength-dependent electron injection, intra-assembly electron transfer, and pH-dependent back electron transfer on TiO(2) were investigated for the molecular assembly [((PO(3)H(2)-CH(2))-bpy)(2)Ru(a)(bpy-NH-CO-trpy)Ru(b)(bpy)(OH(2))](4+) ([TiO(2)-Ru(a)(II)-Ru(b)(II)-OH(2)](4+); ((PO(3)H(2)-CH(2))(2)-bpy = ([2,2'-bipyridine]-4,4'-diylbis(methylene))diphosphonic acid); bpy-ph-NH-CO-trpy = 4-([2,2':6',2″-terpyridin]-4'-yl)-N-((4'-methyl-[2,2'-bipyridin]-4-yl)methyl) benzamide); bpy = 2,2'-bipyridine). This assembly combines a light-harvesting chromophore and a water oxidation catalyst linked by a synthetically flexible saturated bridge designed to enable long-lived charge-separated states.

Sensitized photodecomposition of organic bisphosphonates by singlet oxygen.

During efforts to stabilize metal oxide bound chromophores for photoelectrochemical applications, a novel photochemical reaction has been discovered. In the reaction, the bisphosphonate functional groups -C(PO(3)H(2))(2)(OH) in the metal complex [Ru(bpy)(2)(4,4'-(C(OH)(PO(3)H(2))(2)bpy)](2+) are converted into -COOH and H(3)PO(4). The reaction occurs by sensitized formation of (1)O(2) by the lowest metal-to-ligand charge transfer excited state(s) of [Ru(bpy)(2)(4,4'-(C(PO(3)H(2))(2)(OH))(2)(bpy))](2+)* followed by (1)O(2) oxidation of the bisphosphonate substituent.

Self-assembled bilayers on indium-tin oxide (SAB-ITO) electrodes: a design for chromophore-catalyst photoanodes.

A novel approach for creating assemblies on metal oxide surfaces via the addition of a catalyst overlayer on a chomophore monolayer derivatized surface is described. It is based on the sequential self-assembly of a chromophore, [Ru(bpy)(4,4'-(PO(3)H(2)bpy)(2))](2+), and oxidation catalyst, [Ru(bpy)(P(2)Mebim(2)py)OH(2)](2+), pair, resulting in a spatially separated chromophore-catalyst assembly.

Interfacial dynamics and solar fuel formation in dye-sensitized photoelectrosynthesis cells.

Dye-sensitized photoelectrosynthesis cells (DSPECs) represent a promising approach to solar fuels with solar-energy storage in chemical bonds. The targets are water splitting and carbon dioxide reduction by water to CO, other oxygenates, or hydrocarbons. DSPECs are based on dye-sensitized solar cells (DSSCs) but with photoexcitation driving physically separated solar fuel half reactions.

An amide-linked chromophore-catalyst assembly for water oxidation.

The synthesis and analysis of a new amide-linked, dinuclear [Ru(bpy)(2)(bpy-ph-NH-CO-trpy)Ru(bpy)(OH(2))](4+) (bpy = 2,2'-bipyridine; bpy-ph-NH-CO-trpy = 4-(2,2':6',2"-terpyridin-4'-yl)-N-[(4'-methyl-2,2'-bipyridin-4-yl)methyl]benzamide) assembly that incorporates both a light-harvesting chromophore and a water oxidation catalyst are described. With the saturated methylene linker present, the individual properties of both the chromophore and catalyst are retained including water oxidation catalysis and relatively slow energy transfer from the chromophore excited state to the catalyst.

Photostability of phosphonate-derivatized, Ru(II) polypyridyl complexes on metal oxide surfaces.

The photostability of [Ru(II)(bpy)(2)(4,4'-(PO(3)H(2))(2)bpy)]Cl(2) (bpy = 4,4'-bipyridine) on nanocrystalline TiO(2) and ZrO(2) films was investigated using a standard measurement protocol. Stability was evaluated by monitoring visible light absorbance spectral changes, in real time, during 455 nm photolysis (30 nm fwhm, 475 mW/cm(2)) in a variety of conditions relevant to dye-sensitized solar cells and dye-sensitized photoelectrosynthesis cells. Desorption (k(des)) and photochemical (k(chem)) processes were observed and found to be dependent upon solvent, anion, semiconductor, and presence of oxygen.

Nickel(II) and iron(II) triple helicates assembled from expanded quaterpyridines incorporating flexible linkages.

In the present study the interaction of Fe(II) and Ni(II) with the related expanded quaterpyridines, 1,2-, 1,3- and 1,4-bis-(5'-methyl-[2,2']bipyridinyl-5-ylmethoxy)benzene ligands (4-6 respectively), incorporating flexible, bis-aryl/methylene ether linkages in the bridges between the dipyridyl domains, was shown to predominantly result in the assembly of [M(2)L(3)](4+) complexes; although with 4 and 6 there was also evidence for the (minor) formation of the corresponding [M(4)L(6)](8+) species. Overall, this result contrasts with the behaviour of the essentially rigid 'parent' quaterpyridine 1 for which only tetrahedral [M(4)L(6)](8+) cage species were observed when reacted with various Fe(II) salts. It also contrasts with that observed for 2 and 3 incorporating essentially rigid substituted phenylene and biphenylene bridges between the dipyridyl domains where reaction with Fe(II) and Ni(II) yielded both [M(2)L(3)](4+) and [M(4)L(6)](8+) complex types, but in this case it was the latter species that was assigned as the thermodynamically favoured product type.

New nickel(II) and iron(II) helicates and tetrahedra derived from expanded quaterpyridines.

As an extension of prior studies involving the linear quaterpyridine ligand, 5,5'''-dimethyl-2,2':5',5'':2'',2'''-quaterpyridine 1, the synthesis of the related expanded quaterpyridine derivatives 2 and 3 incorporating dimethoxy-substituted 1,4-phenylene and tetramethoxy-substituted 4,4'-biphenylene bridges between pairs of 2,2'-bipyridyl groups has been carried out via double-Suzuki coupling reactions between 5-bromo-5'-methyl-2'-bipyridine and the appropriate di-pinacol-diboronic esters using microwave heating. Reaction of 2 and 3 with selected Fe(II) or Ni(II) salts yields a mixture of both [M(2)L(3)](4+) triple helicates and [M(4)L(6)](8+) tetrahedra, in particular cases the ratio of the products formed was shown to be dependent on the reaction conditions; the respective products are all sufficiently inert to allow their chromatographic separation and isolation. Longer reaction times and higher concentrations were found to favour tetrahedron formation.

A new FeII quaterpyridyl M4L6 tetrahedron exhibiting selective anion binding.

A rigid linear bis-bidentate quaterpyridine undergoes metal directed self-assembly with iron(ii) salts yielding M(4)L(6) host-guest complexes; selective anion binding for PF(6)(-) over BF(4)(-) is observed.

5,5'-Bis[(trimethyl-silyl)meth-yl]-2,2'-bipyridine.

The mol-ecule of the title compound, C(18)H(28)N(2)Si(2), occupies a special position on an inversion centre. The Si-CH(2)-C(ipso) plane is approximately orthogonal to the plane of the pyridine rings, the corresponding dihedral angle being 82.0 (2)°.