Are Alkynyl Spacers in Ancillary Ligands in Heteroleptic Bis(diimine)copper(I) Dyes Beneficial for Dye Performance in Dye-Sensitized Solar Cells?

The syntheses of 4,40 -bis(4-dimethylaminophenyl)-6,60 -dimethyl-2,20 -bipyridine (1 ), 4,40 -bis(4-dimethylaminophenylethynyl)-6,60 -dimethyl-2,20 -bipyridine (2 ), 4,40 -bis(4- diphenylaminophenyl)-6,60 -dimethyl-2,20 -bipyridine (3 ), and 4,40 -bis(4-diphenylaminophenylethynyl)- 6,60 -dimethyl-2,20 -bipyridine (4 ) are reported along with the preparations and characterisations of their homoleptic copper(I) complexes [CuL2 ][PF6 ] (L = 1 -4 ). The solution absorption spectra of the complexes exhibit ligand-centred absorptions in addition to absorptions in the visible region assigned to a combination of intra-ligand and metal-to-ligand charge-transfer. Heteroleptic [Cu(5 )(Lancillary )]+ dyes in which 5 is the anchoring ligand ((6,60 -dimethyl-[2,20 -bipyridine]- 4,40 -diyl)bis(4,1-phenylene))bis(phosphonic acid) and Lancillary = 1 -4 have been assembled on fluorine-doped tin oxide (FTO)-TiO2 electrodes in dye-sensitized solar cells (DSCs). Performance parameters and external quantum e ciency (EQE) spectra of the DSCs (four fully-masked cells for each dye) reveal that the best performing dyes are [Cu(5 )(1 )]+ and [Cu(5 )(3 )]+ . The alkynyl spacers are not beneficial, leading to a decrease in the short-circuit current density (JSC ), confirmed by lower values of EQEmax . Addition of a co-absorbent (n -decylphosphonic acid) to [Cu(5 )(1 )]+ lead to no significant enhancement of performance for DSCs sensitized with [Cu(5 )(1 )]+ . Electrochemical impedance spectroscopy (EIS) has been used to investigate the interfaces in DSCs; the analysis shows that more favourable electron injection into TiO2 is observed for sensitizers without the alkynyl spacer and confirms higher JSC values for [Cu(5 )(1 )]

Back to the future: asymmetrical DπA 2,2'-bipyridine ligands for homoleptic copper(I)-based dyes in dye-sensitized solar cells

Metal complexes used as sensitizers in dye-sensitized solar cells (DSCs) are conventionally constructed using a push-pull strategy with electron-releasing and electron-withdrawing (anchoring) ligands. In a new paradigm we have designed new D π A ligands incorporating diarylaminophenyl donor substituents and phosphonic acid anchoring groups. These new ligands function as organic dyes. For two separate classes of D π A ligands with 2,2'-bipyridine metal-binding domains, the DSCs containing the copper(I) complexes [Cu(D π A) 2 ] + perform better than the push-pull analogues [Cu(D D )(AA) ] + . Furthermore, we have shown for the first time that the complexes [Cu(D π A) 2 ] + perform better than the organic D π A dye in DSCs. The synthetic studies and the device performances are rationalised with the aid of density functional theory (DFT) and time-dependent DFT (TD-DFT) studies

Asymmetrical DπA 2,2'-diimines for homoleptic copper(I)-based dyes in dye-sensitised solar cells

We live in times of grave precariousness for our environment. It is a proven fact that global warming is mainly caused by the uncontrolled human emissions of CO2 in the atmosphere. The Earth as we know it may irreparably change if we as humans do not take action. The prospects for the future are in rapid change and the temperatures increase must be contained at all costs. In order to do so, new policies must be enforced to promote a conversion of our primary energy sources away from fossil fuels and greatly develop non-emissive sources. Hydroelectric, wind and solar are at the forefront of the renewable energies. The solar sector has been expanding quite rapidly in the last twenty years and will continue to do so. However, the high production costs of silicon solar panels are yet a limiting factor. As described in Chapter 1, the invention of the dye-sensitised solar cell (DSC) paved the way to the development of a rising technology. The DSC is easy to manufacture and its inexpensive production costs are appealing. State-of-the-art devices are sensitised with organic or ruthenium-based dyes. However, ruthenium is a noble metal, its low abundance is responsible of the prohibitive costs, and together with its general toxicity it is unsuitable for commercial applications. Copper(I) is a metal with similar photophysical properties to ruthenium(II), and it is widely available thanks to a greater abundance on the Earth’s crust. In Chapter 2, heteroleptic bis(diiminine) copper(I)-based dyes are initially investigated in the classical push-pull architecture, where two 2,2'-bipyridine ligands are functionalised with an anchoring and electron-donor units. The focus of this chapter is the effects of introducing alkynyl spacers in the ancillary ligand. In Chapters 3–5, an attempt has been made to overcome known issues such as ligand dissociation and to improve the photoconversion efficiencies, by making a shift from the heteroleptic copper(I)-based dyes with the push-pull design to homoleptic copper(I)-based dyes with the alternative [Cu(DπA)2]+ design. Organic dyes bearing a coordinating domain are presented as new asymmetrical DπA 2,2'-bipyridine ligands. The old and the new design are compared thanks to the study of pairs of structural isomers. It is demonstrated that the properties of the [Cu(DπA)2]+ dyes are superior through a thorough analysis of the DSC performances, corroborated by DFT and TD-DFT studies. The properties of these dyes are investigated by structural changes at the 2,2'-bipyridine scaffold. Finally, the properties of the [Cu(DπA)2]+ design are further studied by broadening the scope with 2,2'-biquinoline ligands. Furthermore, one of the presented [Cu(DπA)2]+ dye nears 50% of relative photoconversion efficiency to the reference N719 ruthenium dye, being among the best efficiencies recorded for copper(I)-based dyes

Simulating hydrology with an isotopic land surface model in western Siberia: what do we learn from water isotopes?

International audienceImprovements in the evaluation of land surface models would translate into more reliable predictions of future climate changes, as significant uncertainties persist in the quantification and representation of the relative contributions of soil and vegetation to the water and energy cycles. In this paper, we investigate the usefulness of water stable isotopes in land surface models studying land surface processes. To achieve this, we implemented 18O and 2H and the computation of the oxygen (δ18O) and deuterium (δD) stable isotope composition of soil and leaf water pools in a~recent version of the land surface model ORCHIDEE. We performed point-wise simulations with this new model and evaluated its performance on vertical profiles of soil water isotope ratios measured in summer 2012 at four experimental sites located in a boreal region of the Artic zone of western Siberia. The model performed relatively well in simulating some features of the δ18O soil profiles, but poorly reproduced the d-excess profiles, at all four stations. The response of the simulated δ18O profiles to variations in key hydrological parameters revealed the importance of the choice of a correct infiltration pathway in ORCHIDEE. Our results show also that the strength of the evaporative enrichment signal plays a role in shaping the profiles, too and, therefore, the relevance of the vegetation and bare soil characterization. We investigated furthermore to which extent we are able to determine the relative contribution of the evaporation to the evapotranspiration. This study's results confirm that the use of water stable isotopes measurements helps constrain the representation of key land surface processes in land surface models

Using water isotopes in the evaluation of land surface models

International audienc

Epigenetic alterations in glioblastomas: Diagnostic, prognostic and therapeutic relevance

Glioblastoma, the most common and heterogeneous tumor affecting brain parenchyma, is dismally characterized by a very poor prognosis. Thus, the search of new, more effective treatments is a vital need. Here, we will review the druggable epigenetic features of glioblastomas that are, indeed, currently explored in preclinical studies and in clinical trials for the development of more effective, personalized treatments. In detail, we will review the studies that have led to the identification of epigenetic signatures, IDH mutations, MGMT gene methylation, histone modification alterations, H3K27 mutations and epitranscriptome landscapes of glioblastomas, in each case discussing the corresponding targeted therapies and their potential efficacy. Finally, we will emphasize how recent technological improvements permit to routinely investigate many glioblastoma epigenetic biomarkers in clinical practice, further enforcing the hope that personalized drugs, targeting specific epigenetic features, could be in future a therapeutic option for selected patients

The water isotopic version of the land-surface model ORCHIDEE: implementation, evaluation, sensitivity to hydrological parameters

International audienceLand-Surface Models (LSMs) exhibit large spread and uncertainties in the way they partition precipitation into surface runoff, drainage, transpiration and bare soil evaporation. To explore to what extent water isotope measurements could help evaluate the simulation of the soil water budget in LSMs, water stable isotopes have been implemented in the ORCHIDEE (ORganizing Carbon and Hydrology In Dynamic EcosystEms: the land-surface model) LSM. This article presents this implementation and the evaluation of simulations both in a stand-alone mode and coupled with an atmospheric general circulation model. ORCHIDEE simulates reasonably well the isotopic composition of soil, stem and leaf water compared to local observations at ten measurement sites. When coupled to LMDZ (Laboratoire de Météorologie Dynamique-Zoom: the atmospheric model), it simulates well the isotopic composition of precipitation and river water compared to global observations. Sensitivity tests to LSM (Land-Surface Model) parameters are performed to identify processes whose representation by LSMs could be better evaluated using water isotopic measurements. We find that measured vertical variations in soil water isotopes could help evaluate the representation of infiltration pathways by multi-layer soil models. Measured water isotopes in rivers could help calibrate the partitioning of total runoff into surface runoff and drainage and the residence time scales in underground reservoirs. Finally, co-located isotope measurements in precipitation, vapor and soil water could help estimate the partitioning of infiltrating precipitation into bare soil evaporation