Infrared irradiation-assisted solvent-free Pd-catalyzed (hetero)aryl-aryl coupling via C-H bond activation

The increasing attention towards environmentally friendly synthetic protocols has boosted studies directed to the development of green and sustainable methods for direct C−H bond arylation of (hetero)arenes. In this context, here the infrared (IR) irradiation-assisted solvent-free Pd-catalyzed direct C−H bond arylation of (hetero)arenes was achieved. Several heteroaryl-aryl coupling reactions were described, also involving heterocycles commonly used as building blocks for the synthesis of organic semiconductors. The reaction tolerated many functional groups on the aromatic nuclei. The IR-irradiation as the energy source compared favorably with thermal heating and, in combination with solvent-free conditions, provided an important contribution to the development of protocols fitting with the principles of green chemistry

Effect of Posttreatment of Titania Mesoscopic Films by TiCl4 in Solid- State Dye-Sensitized Solar Cells: A Time-Resolved Spectroscopy Study

Post-treatment of mesoporous titanium dioxide films by TiCl4 solutions is commonly applied during the fabrication of solid-state dye-sensitized solar cells (ssDSCs), as this operation markedly improves the performance of the photovoltaic device. The effect of the post-treatement upon the charge carrier dynamics was scrutinized in ssDSC aiming at unraveling its mechanism. Kinetic studies carried out using femtosecond and nanosecond transient absorption spectroscopy, showed that a biphasic electron injection from the dye excited state is observed, for both treated and non-treated films, which kinetics is not significantly affected by the surface modification step. However, hole injection in the hole transport material (HTM) spiro-OMeTAD and charge recombination were found to be markedly slower in TiCl4-treated films. These findings are rationalized by a model describing the interaction at the interface between TiO2, the dye-sensitizer and spiro-OMeTAD. Rather than resulting from a modification of the energetics of the conduction band of the oxide, the effect of the TiCl4 post-treatment appears to be associated with a subtle change of the film morphology. Results emphasize the importance of controlling the contact at the heterojunction between the HTM and the sensitized semiconductor oxide network

Applicazioni di acido abscissico in ‘Crimson Seedless’ per migliorare la colorazione delle bacche

Tra le cultivar ad uva da tavola a bacca rossa coltivate in Puglia, la 'Crirnson seedless' è una delle più importanti per il contributo produnivo offerto alla produzione totale regionale. È una cultivar molto interessante per l'epoca medio-tardiva di maturazione (settembre-ottobre), per produttività, per caratteri qualitativi (pezzatura, consistenza e sapore della bacca), ma presenta frequentemente una colorazione dell'epicarpo non adeguata agli standard commerciali. La difformità di colorazione delle bacche, osservata nei climi caldo-aridi, può dipendere sia dalle elevate temperature estive che dalle limitate escursioni termiche giorno/notte che ostacolano l'accumulo di antociani nell'epicarpo. Per migliorare la colorazione delle bacche della cultivar 'Crimson seedless' si è pensato di ricorrere all 'applicazione dell' acido abscissico (SABA), verificando gli effetti dello stesso sulla qualità generale dell'uva e determinandone la concentrazione nelle bacche alla raccolta. Nell'annata 2010-2011 è stata condotta una prova in un vigneto commerciale di 'Crirnson seedless' in agro di Rutigliano (Ba) per valutare gli effetti dell'S-ABA sulla colorazione e su altri aspetti qualitativi dell'uva. Una formulazione commerciale di S-ABA (ProTone®) è stata impiegata a due concentrazioni (200 e 400 mg/L) ed in diverse epoche a partire dall 'invaiatura. I risultati ottenuti hanno indicato che, al momento della raccolta, l'applicazione di S-ABA ha significativamente influenzato i parametri del colore dell'epicarpo. In particolare, i grappoli trattati con S-ABA alla concentrazione maggiore all'invaiatura si sono colorati prima ed in maniera più uniforme rispetto al testimone, con conseguente anticipo della raccolta di circa 15 giorni, aspetto molto importante dal punto di vista commerciale. Alla raccolta, i valori di consistenza della bacca, °Brix , pH e acidità titolabile non hanno mostrato differenze significative fra i trattamenti. In conclusione, l'applicazione di S-ABA ha svolto un positivo effetto sul colore dell'epicarpo delle bacche di 'Crimson seedless', migllorandone la colorazione commerciale che è stata raggiunta in anticipo

Photoinduced Interfacial Electron Injection Dynamics in Dye-Sensitized Solar Cells under Photovoltaic Operating Conditions

We report a pump–probe spectroscopy study of electron injection rates in dye-sensitized solar cell (DSSC) devices. We examine the case of working devices employing an N719 ruthenium sensitizer and an iodide electrolyte. Electron injection is found to occur mainly on a sub-100 fs time scale, followed by a slower component with a lifetime of 26.9 ps, in accordance with previous reports on model samples. The amplitude of this latter component varies with electrolyte composition from 25 to 9%. The appearance of slower components in the electron injection dynamics may be attributed to an aggregated or weakly bound state of the surface-adsorbed N719 sensitizer. Further measurements are reported varying the cell light bias and load conditions, revealing no influence on electron injection dynamics. No other electron injection event is found to occur up to 1 ns. These results show no evidence for a slowdown of electron injection under working conditions compared to model systems for the electrolytes examined in this study

Photoinduced interfacial electron transfer and lateral charge transport in molecular donor–acceptor photovoltaic systems

Nanostructured liquid|solid and solid|solid bulk heterojunctions designed for the conversion of solar energy offer ideal models for the investigation of light-induced ET dynamics at surfaces. Despite significant study of processes leading to charge generation in third-generation solar cells, a conclusive picture of the photophysics of these photovoltaic converters is still missing. More specifically searched is the link between the molecular structure of the interface and the kinetics of surface photoredox reactions. Fundamental scientific issues in this field are addressed by the research project undertaken in the frame of the NCCR-MUST endeavor, an outline of which is given here

Dynamics and mechanisms of interfacial photoinduced electron transfer processes of third generation photovoltaics and photocatalysis

Photoinduced electron transfer (PET) across molecular/bulk interfaces has gained attention only recently and is still poorly understood. These interfaces offer an excellent case study, pertinent to a variety of photovoltaic systems, photo- and electrochemistry, molecular electronics, analytical detection, photography, and quantum confinement devices. They play in particular a key role in the emerging fields of third-generation photovoltaic energy converters and artificial photosynthetic systems aiming at the production of solar fuels, creating a need for a better understanding and theoretical treatment of the dynamics and mechanisms of interfacial PET processes. We aim at achieving fundamental understanding of these phenomena by designing experiments that can be used to test and alter modern theory and computational modeling. One example illustrating recent investigations into the details of the ultrafast processes that form the basis for photoinduced charge separation at a molecular/bulk interface relevant to dye-sensitized solar cells is briefly presented here. Kinetics of interfacial PET and charge recombination processes were measured by fs and ns transient spectroscopy in a heterogeneous donor-bridge-acceptor (D-B-A) system, where D is a RuII(terpyridyl-PO3)(NCS)3 complex, B an oligo-p-phenylene bridge, and A nanocrystalline TiO2. The forward ET reaction was found to be faster than the vibrational relaxation of the vibronically excited state of the donor. Instead, the back ET occurred on the μs time scale and involved fully thermalized species. The D-A distance dependence of the electron transfer rate was studied by varying the number of p-phenylene units contained in the bridge moiety. The remarkably low damping factor β = 0.16 Å–1 observed for the ultrafast charge injection from the dye excited state into the conduction band of TiO2 is attributed to the coupling of electron tunneling with non-equilibrium vibrations redistributed on the bridge, giving rise to polaronic transport of charges from the donor ligand to the acceptor solid oxide surface

The Effect of Hole Transport Material Pore Filling on Photovoltaic Performance in Solid-State Dye-Sensitized Solar Cells

A detailed investigation of the effect of hole transport material (HTM) pore filling on the photovoltaic performance of solid-state dye-sensitized solar cells (ss-DSCs) and the specific mechanisms involved is reported. It is demonstrated that the efficiency and photovoltaic characteristics of ss-DSCs improve with the pore filling fraction (PFF) of the HTM, 2,2’,7,7’-tetrakis-( N, N-di-p-methoxyphenylamine)9,9’-spirobifluorene(spiro-OMeTAD). The mechanisms through which the improvement of photovoltaic characteristics takes place were studied with transient absorption spectroscopy and transient photovoltage/photocurrent measurements. It is shown that as the spiro- OMeTAD PFF is increased from 26% to 65%, there is a higher hole injection efficiency from dye cations to spiro-OMeTAD because more dye molecules are covered with spiro-OMeTAD, an order-of-magnitude slower recombination rate because holes can diffuse further away from the dye/HTM interface, and a 50% higher ambipolar diffusion coefficient due to an improved percolation network. Device simulations predict that if 100% PFF could be achieved for thicker devices, the efficiency of ss-DSCs using a conventional ruthenium dye would increase by 25% beyond its current value

Precision measurements of the top quark mass from the Tevatron in the pre-LHC era

The top quark is the heaviest of the six quarks of the Standard Model. Precise knowledge of its mass is important for imposing constraints on a number of physics processes, including interactions of the as yet unobserved Higgs boson. The Higgs boson is the only missing particle of the Standard Model, central to the electroweak symmetry breaking mechanism and generation of particle masses. In this Review, experimental measurements of the top quark mass accomplished at the Tevatron, a proton-antiproton collider located at the Fermi National Accelerator Laboratory, are described. Topologies of top quark events and methods used to separate signal events from background sources are discussed. Data analysis techniques used to extract information about the top mass value are reviewed. The combination of several most precise measurements performed with the two Tevatron particle detectors, CDF and \D0, yields a value of \Mt = 173.2 \pm 0.9 GeV/$c^2$.Comment: This version contains the most up-to-date top quark mass averag

Search for large extra dimensions in the production of jets and missing transverse energy in p(p)over-bar collisions at root s=1.96 TeV

We present the results of a search for new physics in the jets plus missing transverse energy data sample collected from 368 pb(-1) of p (p) over bar collisions at root s = 1.96 TeV recorded by the Collider Detector at Fermilab. We compare the number of events observed in the data with a data-based estimate of the standard model backgrounds contributing to this signature. We observe no significant excess of events, and we interpret this null result in terms of lower limits on the fundamental Planck scale for a large extra dimensions scenario

Measurement of the W+W- production cross section in p(p)over-bar collisions at root s=1.96 TeV using dilepton events

We present a measurement of the W+W- production cross section using 184 pb(-1) of p (p) over bar collisions at a center-of-mass energy of 1.96 TeV collected with the Collider Detector at Fermilab. Using the dilepton decay channel W+W-→ l(+)ν l(-)(ν) over bar, where the charged leptons can be either electrons or muons, we find 17 candidate events compared to an expected background of 5.0(-0.8)(+2.2) events. The resulting W+W- production cross-section measurement of σ(p (p) over bar → W+W-)=14.6(-5.1)(+5.8)(stat)(-3.0)(+1.8)(syst)± 0.9(lum) pb agrees well with the standard model expectation