Exploring simple ancillary ligands in copper-based dye-sensitized solar cells: effects of a heteroatom switch and of co-sensitization

The copper( I ) complexes [Cu(1) 2 ][PF 6 ], [Cu(2) 2 ][PF 6 ], [Cu(3) 2 ][PF 6 ] and [Cu(4) 2 ][PF 6 ] (1 . 2-(1H-imidazol-2-yl)- 6-methylpyridine, 2 . 2-(6-methylpyridin-2-yl)oxazole, 3 . 2-(6-methylpyridin-2-yl)thiazole and 4 . 2- methyl-6-(1-methyl-1H-imidazol-2-yl)pyridine) are reported. The crystal structures of [Cu(2) 2 ][PF 6 ]$ 0.5CH 2 Cl 2 and [Cu(3) 2 ][PF 6 ] confirm N,N 0 -chelation modes for 2 and 3, and tetrahedral copper( I ). In the solution absorption spectra, the MLCT band shifts to lower energy with a change in heteroatom (O, 424 nm; NH, 435 nm; NMe, 446 nm; S, 465 nm). [Cu(1) 2 ][PF 6 ] and [Cu(4) 2 ][PF 6 ] undergo copper-centred oxidative processes at lower potential than the complexes with O or S heteroatoms. Heteroleptic complexes [Cu(5)(L)] + (5 . ((6,6 0 -dimethyl-[2,2 0 -bipyridine]-4,4 0 -diyl)bis(4,1-phenylene)bis(phosphonic acid)), L . 1–4) were assembled on FTO/TiO 2 electrodes. The shift in the MLCT band (O NH < NMe < S) in the solid-state absorption spectra of the dye-functionalized electrodes parallels that of solution. The photoconversion efficiencies (h) of masked, dye-sensitized solar cells (DSCs) containing [Cu(5)(L)] + (L . 1– 4) dyes and an I/I 3 redox shuttle follow the order [Cu(5)(1)] + (3.03%) > [Cu(5)(3)] + (2.88%) > [Cu(5)(4)] + (2.71%) > [Cu(5)(2)] + (2.62%) relative to 7.55% for N719. Ancillary ligand 1 (with NH) leads to the highest open-circuit voltage (V OC . 608 mV) whilst 3 (S-heteroatom) gives the highest short-circuit current density (J SC . 7.76 mA cm 2 ). The performances of [Cu(5)(1)] + and [Cu(5)(3)] + are understood with the aid of electrochemical impedance spectroscopy (EIS). The DSC with [Cu(5)(1)] + exhibits a high chemical capacitance (C m ) and a low recombination resistance (R rec ); since the latter is offset by a low transport resistance (R tr ), a high J SC and V OC are observed for [Cu(5)(1)] + . DSCs with [Cu(5)(3)] + have the lowest R tr of all four devices. The performance of DSCs sensitized by a combination of [Cu(5)(1)] + and [Cu(5)(3)] + were assessed in order to capitalize upon the high V OC of [Cu(5)(1)] + and the high J SC of [Cu(5)(3)] + . After FTO/ TiO 2 functionalization with anchor 5, the electrodes were treated with a 1 : 1 mix of [Cu(5)(1)] + and [Cu(5)(3)] + or sequentially with [Cu(5)(3)] + then [Cu(5)(1)] + , or [Cu(5)(1)] + then [Cu(5)(3)] + . The DSC performances and the EIS parameters are consistent with competition between 1 and 3 for surface binding-sites; 1 dominates over 3, both in binding and in contribution to the overall photoresponse

Enforcing Multifunctionality: A Pressure-Induced Spin-Crossover Photomagnet

Photomagnetic compounds are usually achieved by assembling preorganized individual molecules into rationally designed molecular architectures via the bottom-up approach. Here we show that a magnetic response to light can also be enforced in a nonphotomagnetic compound by applying mechanical stress. The nonphotomagnetic cyano-bridged Fe^II–Nb^IV coordination polymer {[Fe^II(pyrazole)₄]₂[Nb^IV(CN)₈]·4H₂O}_<i>n</i> (<b>FeNb</b>) has been subjected to high-pressure structural, magnetic and photomagnetic studies at low temperature, which revealed a wide spectrum of pressure-related functionalities including the light-induced magnetization. The multifunctionality of <b>FeNb</b> is compared with a simple structural and magnetic pressure response of its analog {[Mn^II(pyrazole)₄]₂[Nb^IV(CN)₈]·4H₂O}_<i>n</i> (<b>MnNb</b>). The <b>FeNb</b> coordination polymer is the first pressure-induced spin-crossover photomagnet

Hexafluoridophosphate partial hydrolysis leading to the one-dimensional coordination polymer [{Cu(xantphos)(µ-PO2F2)}n]

The one-dimensional coordination polymer [{Cu(xantphos)(μ-PO2F2)}n] (xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) is reported, the first extended structure in which copper(I) centres are linked by μ-PO2F2 units

Codigestione anaerobica di rifiuti urbani provenienti da raccolta differenziata e fanghi di supero

Atti delle Giornate di Studio tenutesi a Milano nel 1987 e nel 1988

The beneficial effects of trifluoromethyl-substituents on the photoconversion efficiency of copper(I) dyes in dye-sensitized solar cells

The synthesis and characterization of [Cu(2)2][PF6] and [Cu(3)2][PF6] in which 2 1/4 6,60-bis(trifluoromethyl)- 2,20-bipyridine and 3 1/4 6-trifluoromethyl-2,20-bipyridine are reported. The single crystal structure of [Cu(2)2][PF6] confirms that the copper(I) centre is sterically protected by the four CF3 groups in a near regular tetrahedral environment. The Cu+/Cu2+ oxidation potential is shifted from +0.44 to +0.72 V on going from [Cu(1)2][PF6] to [Cu(2)2][PF6] (1 1/4 6,60-dimethyl-2,20-bipyridine), in keeping with the electronwithdrawing effects of the CF3 groups. 1H and 19F NMR spectroscopic data for a CH2Cl2 solution containing [Cu(1)2][PF6] and [Cu(2)2][PF6] demonstrate that the ligands in [Cu(2)2][PF6] remain highly labile. An on-surface procedure was used to assemble the dyes [Cu(4)(2)]+ and [Cu(4)(3)]+ (4 1/4 anchoring ligand ((6,60-dimethyl-[2,20-bipyridine]-4,40-diyl)bis(4,1-phenylene))bis(phosphonic acid)) on TiO2; solid-state adsorption spectra show that dye coverage for [Cu(4)(3)][PF6] exceeds that of [Cu(4)(2)]- [PF6]. The performances of the dyes in dye-sensitized solar cells (DSCs) are compared with that of [Cu(4)(1)]+. DSCs containing the fluorinated ancillary ligands exhibit photoconversion efficiencies of z30–34% relative to N719 set at 100%; this is a significant enhancement with respect to DSCs containing [Cu(4)(1)]+ with no fluoro-groups. Density functional theory (DFT) calculations for the heteroleptic dyes demonstrate that the HOMO is stabilized upon introduction of the CF3 groups, but that the compositions of the molecular orbitals in the HOMO–LUMO manifold are little changed. The improved DSC performance is associated with enhanced short-circuit current density (JSC) for [Cu(4)(3)]+ and [Cu(4)(2)]+ versus [Cu(4)(1)]+; this is also seen in high EQEmax values of 46% for [Cu(4)(2)]+ and 51% for [Cu(4)(3)]+ (both at lmax 1/4 480 nm)

Towards laser-manipulated deposition for atom-scale technologies

We have developed an apparatus for nanostructure fabrication based on direct deposition of laser-manipulated cesium vapors onto pyrolitic graphite. Key features of our apparatus are production and manipulation of a longitudinally cooled atom beam, which allows for straightforward operation in the moderate to low flux density conditions. Both unstructured and structured low surface coverage depositions have been carried out and samples carefully analyzed at the atom scale by in situ tunneling microscopy. Results represent a step forward to the realization of a novel technology for spacecontrolled deposition of few, eventually single, atoms. (C) 2009 Elsevier B.V. All rights reserved