Design and development of new organic molecules as alternative fluorophores for LSC application

Presently, Luminescent Solar Concentrators (LSCs) are considered promising alternative optical devices for the sunlight harvest and production of energy. A LSC is composed by a thin transparent polymer slab, doped with a fluorophore able to absorb solar radiation and concentrate it, at a specific wavelength, at the edges of the slab, where a thin PV cell can capture and use to produce electricity. Due to the low-priced materials and their innovative aesthetic properties, LSCs find an easy integration in architectural systems, such as roofs, windows, canopies and greenhouse. The heart of LSC device remains fluorophore, which needs to follow several optoelectronic properties: broad absorption range, long-wavelength emission maximum, large Stokes shift, high fluorescence quantum yield, low-priced materials and production, good optical efficiency and good dispersion in the host materials. The organic molecules are more versatile class of luminophores, which can largely satisfy LSC requirements, due to their close relationship between molecular design and optoelectronic tunability. During this Ph.D., keeping in mind all these targets, a careful and specific molecular design supported by computational analysis have been accomplished. Three classes of new organic fluorophores characterized by D-A-D structure have been planned and executed. The synthetic optimization and the employment of sustainable procedures have been carried out when possible, favoring cross-coupling reactions and more eco-friendly approaches. All organic chromophores have spectroscopically characterized in solution and polymer dispersion, designing a common prototype of LSC device for all chromophores. Alternative matrices have been tested to evaluate their impact on optoelectronic properties of the various fluorophores. LSC performances of each chromophore have been assessed and compared with those of literature reference Lumogen F Red 305 (LR305)

Green/Yellow-Emitting Conjugated Heterocyclic Fluorophores for Luminescent Solar Concentrators

In this study, we report on the synthesis of new organic fluorophores containing either the benzo[1,2-d:4,5-d]bisthiazole or the dithieno[3,2-b:2,3-d]silole heterocyclic unit, and on their application for the fabrication of luminescent solar concentrators (LSCs) made of poly(methyl methacrylate) (PMMA) thin films. In solution, the new compounds absorbed light in the visible region and displayed a brilliant green emission in the 500-600 nm range with moderate-to-good fluorescence quantum yields (0.25-0.68). Dispersions of selected fluorophores in PMMA thin films mostly maintained the light absorption features observed in solution, although in the case of benzobisthiazole-based fluorophore 1a an evident fluorescence red-shift was observed when increasing the compound concentration in the film. In agreement with its promising optical properties, LSCs prepared with the latter compound yielded interesting optical efficiencies up to 6.42%, not far from those of state-of-the-art PMMA LSC devices

Luminescent solar concentrators with outstanding optical properties by employment of D–A–D quinoxaline fluorophores

Luminescent solar concentrators (LSCs) are devices designed to efficiently collect both direct and diffuse solar radiation and concentrate it on photovoltaic cells to foster their use in building-integrated photovoltaics (BIPV). The optimization of LSC performances involves the adjustment of both the fluorophore and the guest polymer matrix. On this account, we investigated a series of high quantum yield, donor-acceptor-donor (D-A-D) photostable fluorophores (DQ1-5), presenting a central quinoxalinic acceptor core, not previously employed in LSCs, and triarylamines or phenothiazine as donor groups. The molecules were also decorated with alkyl chains on the central core and/or the donor groups, to explore their compatibility with the poly(methyl methacrylate) (PMMA) and poly(cyclohexyl methacrylate) (PCMA) matrices utilized in this study. The PMMA and PCMA films (25 mu m thick), containing 0.2-2.2 wt% of DQ1-5, absorbed in the 370-550 nm range and presented emission maxima at 550-600 nm, with fluorescence quantum yields higher than 40% even at the highest doping contents. Notably, the DQ1/PMMA thin-films showed enhanced phase compatibility and excellent quantum yields, i.e., >95%. Accordingly, they were designed to obtain 25 cm(2) area LSCs with remarkable internal (eta(int)) and external (eta(ext)) photon efficiencies of 42.9% and 6.2%, respectively, higher than those observed from state-of-the-art devices based on the Lumogen Red 305 (LR305) as the reference fluorophore. Overall, these were the best results ever achieved in our laboratory for thin-film LSCs built with organic fluorescent emitters

Search for electroweak production of charginos and neutralinos using leptonic final states in pp collisions at s=7\sqrt{s} = 7 TeV

The 2011 dataset of the CMS experiment, consisting of an integrated luminosity of 4.98 inverse femtobarns of pp collisions at sqrt(s) = 7 TeV, enables expanded searches for direct electroweak pair production of charginos and neutralinos in supersymmetric models as well as their analogs in other models of new physics. Searches sensitive to such processes, with decays to final states that contain two or more leptons, are presented. Final states with three leptons, with a same-sign lepton pair, and with an opposite-sign lepton pair in conjunction with two jets, are examined. No excesses above the standard model expectations are observed. The results are used in conjunction with previous results on four-lepton final states to exclude a range of chargino and neutralino masses from approximately 200 to 500 GeV in the context of models that assume large branching fractions of charginos and neutralinos to leptons and vector bosons.Comment: Replaced with published version. Added journal reference and DO