Laura Teruel

Periodic mesoporous silica having covalently attached tris(bipyridine)ruthenium complex: synthesis, photovoltaic and electrochemiluminescent properties

A tris(bipyridine)ruthenium derivative with two terminal triethoxysilyl groups attached to one of the bipyridine ligands has been synthesized and used in combination with TEOS for the preparation of a tris(bipyridine)ruthenium-containing mesoporous silica, using CTABr as a structure-directing agent, under basic conditions at 100 °C. The resulting solids exhibited XRD patterns, isothermal gas adsorption and electron-microscopy images characteristic of hexagonal mesoporous silica, while the presence of tris(bipyridine)ruthenium complexes at the walls is manifested by the orange coloration of the solids and the optical spectra of the material corresponding to tris(bipyridine)ruthenium(II). The removal of the structure-directing agent without damaging the complex or the mesoporous structure of the pores was done by exhaustive solid–liquid extraction. As-synthesized mpRu exhibits photovoltaic (VOC = 140 mV, ISC = 2.6 µA) and electrochemiluminescence activity (λmax = 610 nm), the presence of CTABr plays a positive role in the activity by promoting intraparticle charge migration. In contrast, for an analogous material prepared under the same conditions but in the absence of the structure-directing agent and having a low surface area, the amorphous structure did not exhibit significant a photovoltaic or electrochemiluminescence response. This result exemplifies the benefits of having porosity and accessibility to the photoactive metallic complexes.

Hydrotalcites of zinc and titanium as precursors of finely dispersed mixed oxide semiconductors for dye-sensitized solar cells

Hydrotalcites are layered materials whose sheets are constituted by octahedra occupied by two different metals (one divalent and the other tri- or tetravalent) and having oxide or hydroxide at the corners. The excess of positive charge of the sheets is compensated by anions located at the interlamellar space. In the present work we have synthesized two hydrotalcites containing zinc and titanium (Zn/Ti atomic ratio in the gel synthesis 6.25) that differ on the absence or presence of sodium dodecyl sulfate in the interlamellar spaces. Calcination of these hydrotalcites leads to a film of intimately dispersed mixed oxide semiconductor that was used as semiconductor for dye sensitised solar cells. Using a ruthenium polypyridyl complex as dye, two photovoltaic cells constructed by films of mixed oxides derived from hydrotalcite calcination were prepared. The highest efficiency parameters were VOC = 0.63 V, JSC = 2.18 mA cm−2, FF = 0.465, η = 0.64%. These efficiency values are not far from those obtained for an analogous photovoltaic cell prepared using P25 titania.

Structured Mesoporous Tin Oxide with Electrical Conductivity. Application in Electroluminescence

Tin oxide nanoparticles (2-5 nm) have been structured using CTAB surfactant into mesoporous mpSnO(2) materials that exhibit lower electrical resistivity than the precursors SnO(2) nanoparticles and over nine orders the magnitude lower than that of mesoporous MCM-41 silica. The superior performance of these conductive mesoporous mpSnO(2) materials as hosts is clearly manifested by the fact that a conjugated polymer with 2,5-dimethoxyphenylenevinylene structure emits light at voltages below 10 V direct current when incorporated in mpSnO(2) materials, but not in analogous mesoporous MCM-41 silica or when adsorbed on the nonporous precursor SnO(2) nanoparticles.

Organosilica Spheres Covalently Functionalized with Diphenylanthracene and Viologen Units

Organosilica spheres functionalized with two different photoactive units, diphenylanthracene, DPA@SPH, and viologen, VIO@SPH, covalently linked to the silica framework are prepared. These new materials have a uniform diameter, 300 nm for the DPA@SPH and 550 nm for the VIO@SPH, and exhibit the typical photochemical response of the organic moieties. It is observed that organic radical cations incorporated in the structure of the functionalized silica spheres are remarkably persistent. Due to their morphology and regular diameter DPA@SPH do not tend to aggregate and they form a highly regular, ordered and homogeneous multilayer film of high surface coverage which is employed as the active layer for the preparation of an electroluminescence cell.

Unexpected photochemistry and charge-transfer complexes of [CB11H12]2 carborane

Although the [CB(11)H(12)](-) carborane does not exhibit an absorption band in UV, its triplet excited state can be generated upon 308 nm laser excitation; also unexpectedly carborane acts as electron donor forming a charge transfer complex with methylviologen that upon illumination gives rise to viologen radical cation.