Homoleptic imidazolate frameworks (3)(infinity)[Sr1-xEux(Im)(2)]-hybrid materials with efficient and tuneable luminescence.

Homoleptic frameworks of the formula 3∞[Sr1−xEux(Im)2] (1) x = 0.01–1.0; Im− = imidazolate anion, C3H3N2−) are hybrid materials that exhibit an intensive green luminescence. Tuning of both emission wavelength and quantum yield is achieved by europium/strontium substitution so that a QE of 80% is reached at a Eu content of 5%. Even 100% pure europium imidazolate still shows 60% absolute quantum efficiency. Substitution of Sr/Eu shows that doping with metal cations can also be utilized for coordination compounds to optimize materials properties. The emission is finely tuneable in the region 495–508 nm via variation of the europium content. The series of frameworks 3∞[Sr1−xEux(Im)2] presents dense MOFs with the highest quantum yields reported for MOFs so far

Luminescence tuning of MOFs via ligand to metal and metal to metal energy transfer by co-doping of 2∞[Gd2Cl6(bipy)3]*2bipy with europium and terbium

The series of anhydrous lanthanide chlorides LnCl3, Ln=Pr–Tb, and 4,4'-bipyridine (bipy) constitute isotypic MOFs of the formula 2∞[Ln2Cl6(bipy)3]*2bipy. The europium and terbium containing compounds both exhibit luminescence of the referring trivalent lanthanide ions, giving a red luminescence for Eu3+ and a green luminescence for Tb3+ triggered by an efficient antenna effect of the 4,4'-bipyridine linkers. Mixing of different lanthanides in one MOF structure was undertaken to investigate the potential of this MOF system for colour tuning of the luminescence. Based on the gadolinium containing compound, co-doping with different amounts of europium and terbium proves successful and yields solid solutions of the formula 2∞[Gd2-x-yEuxTbyCl6(bipy)3]*2bipy (1–8), 0≤x, y≤0.5. The series of MOFs exhibits the opportunity of tuning the emission colour in-between green and red. Depending on the atomic ratio Gd:Eu:Tb, the yellow region was covered for the first time for an oxygen/carboxylate-free MOF system. In addition to a ligand to metal energy transfer (LMET) from the lowest ligand-centered triplet state of 4,4'-bipyridine, a metal to metal energy transfer (MMET) between 4f-levels from Tb3+ to Eu3+ is as well vital for the emission colour. However, no involvement of Gd3+ in energy transfers is observed rendering it a suitable host lattice ion and connectivity centre for diluting the other two rare earth ions in the solid state. The materials retain their luminescence during activation of the MOFs for microporosity

Temperature-Dependent Polarized Raman Spectra of CaFe2O4

The Raman spectra of CaFe2O4 were measured with several exact scattering configurations between 20 and 520K and the symmetry of all observed Raman lines was determined. The Ag and B2g lines were assigned to definite phonon modes by comparison to the results of lattice dynamical calculations. No anomaly of phonon parameters was observed near the magnetic ordering temperature TN = 160K.Comment: 4 pages, 1 table, 4 figure

Molecularly imprinted conductive polymers for controlled trafficking of neurotransmitters at solid–liquid interfaces

We realize a molecularly imprinted polymer (MIP) which is imprinted with the retinal neurotransmitter glutamate. The films prepared by electrochemical deposition have a smooth surface with a granular morphology as observed using an atomic force microscope. Multiple reflection attenuated total reflection infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) are used to chemically confirm the imprint of a neurotransmitter in the MIP at the solid–liquid and the solid–air interface, respectively. Fluorescence spectroscopy using the dye fluorescamine is used to monitor the changes in neurotransmitter concentration in various solvents induced by application of voltage to the MIP. By controlling neurotransmitter trafficking across a solid–liquid interface with voltage, we suggest the possibility of using such a neurotransmitter imprinted MIP for chemical stimulation of retinal neurons. The current state of the art approach to restore sight in certain cases of blindness is the replacement of damaged photoreceptors by a subretinal implant consisting of light-sensitive photodiodes. Thus a future perspective of our work would be to chemically stimulate the neurons by replacing the photodiodes in the subretinal implant by the neurotransmitter imprinted polymer film

Tuneable interfacial surfactant aggregates mimic lyotropic phases and facilitate large scale nanopatterning.

It is shown that the air-liquid interface can be made to display the same rich curvature phenomena as common lyotropic liquid crystal systems. Through mixing an insoluble, naturally occurring, branched fatty acid, with an unbranched fatty acid of the same length, systematic variation in the packing constraints at the air-water interface could be obtained. The combination of atomic force microscopy and neutron reflectometry is used to demonstrate that the water surface exhibits significant tuneable topography. By systematic variation of the two fatty acid proportions, ordered arrays of monodisperse spherical caps, cylindrical sections, and a mesh phase are all observed, as well as the expected lamellar structure. The tuneable deformability of the air-water interface permits this hitherto unexplored topological diversity, which is analogous to the phase elaboration displayed by amphiphiles in solution. It offers a wealth of novel possibilities for the tailoring of nanostructure

Correlation of Thermoelectric Performance, Domain Morphology and Doping Level in PEDOT:PSS Thin Films Post-Treated with Ionic Liquids.

AbstractIonic liquid (IL) post‐treatment of poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) thin films with ethyl‐3‐methylimidazolium dicyanamide (EMIM DCA), allyl‐3‐methylimidazolium dicyanamide (AMIM DCA), and 1‐ethyl‐3‐methylimidazolium tetracyanoborate (EMIM TCB) is compared. Doping level modifications of PEDOT are characterized using UV–Vis spectroscopy and directly correlate with the observed Seebeck coefficient enhancement. With conductive atomic force microscopy (c‐AFM) the authors investigate changes in the topographic‐current features of the PEDOT:PSS thin film surface due to IL treatment. Grazing incidence small‐angle X‐ray scattering (GISAXS) demonstrates the morphological rearrangement towards an optimized PEDOT domain distribution upon IL post‐treatment, directly facilitating the interconductivity and causing an increased film conductivity. Based on these improvements in Seebeck coefficient and conductivity, the power factor is increased up to 236 µW m−1K−2. Subsequently, a model is developed indicating that ILs, which contain small, sterically unhindered ions with a strong localized charge, appear beneficial to boost the thermoelectric performance of post‐treated PEDOT:PSS films

Effect of Blend Composition and Additives on the Morphology of PCPDTBT:PC71BM Thin Films for Organic Photovoltaics.

The use of solvent additives in the fabrication of bulk heterojunction polymer:fullerene solar cells allows to boost efficiencies in several low bandgap polymeric systems. It is known that solvent additives tune the nanometer scale morphology of the bulk heterojunction. The full mechanism of efficiency improvement is, however, not completely understood. In this work, we investigate the influences of blend composition and the addition of 3 vol % 1,8-octanedithiol (ODT) as solvent additive on polymer crystallization and both, vertical and lateral morphologies of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] and [6,6]-phenyl C71-butyric acid methyl ester (PCPDTBT:PC71BM) blend thin films processed from chlorobenzene-based solutions. The nanoscale morphology is probed with grazing incidence small- and wide-angle X-ray scattering as well as X-ray reflectivity and complemented with UV/vis spectroscopy. In PCPDTBT:PC71BM films the use of ODT is found to lower the solubility of fullerene in the polymer matrix and to promote polymer crystallization, both vertical and lateral microphase separation with morphological coarsening, and formation of a fullerene-rich topping layer. The enhanced photovoltaic performance is explained by these findings