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Borexino, a large volume detector for low energy neutrino spectroscopy, is currently running underground at the Laboratori Nazionali del Gran Sasso, Italy. The main goal of the experiment is the real-time measurement of sub MeV solar neutrinos, and particularly of the mono energetic (862 keV) Be7 electron capture neutrinos, via neutrino-electron scattering in an ultra-pure liquid scintillator. This paper is mostly devoted to the description of the detector structure, the photomultipliers, the electronics, and the trigger and calibration systems. The real performance of the detector, which always meets, and sometimes exceeds, design expectations, is also shown. Some important aspects of the Borexino project, i.e. the fluid handling plants, the purification techniques and the filling procedures, are not covered in this paper and are, or will be, published elsewhere (see Introduction and Bibliography)

The solvent effect on the photophysical and photochemical properties of the iodides of three trans (E) isomers of 2-D-vinyl,1-methylpyridinium, where D is a donor group (4-dimethylaminophenyl, 3,4,5-trimethoxyphenyl and 1-pyrenyl), was studied by stationary and transient absorption techniques. The results obtained allowed the negative solvatochromism and relaxation pathways of the excited states in the singlet manifold to be reasonably interpreted. Resorting to ultrafast absorption techniques and DFT calculations allowed information on the excited state dynamics and the role of the solvent-controlled intramolecular charge transfer (ICT) processes to be obtained. The structure-dependent excited state dynamics in nonpolar solvents, where the ICT is slower than solvent rearrangement, and in polar solvents, where an opposite situation is operative, was thus explained. The push-pull character of the three compounds, particularly the anilino-derivative, suggests their potential application in optoelectronics.

We report the direct measurement of the 7 Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV 7 Be neutrinos is 49±3stat±4syst counts/(day·100 ton). The hypothesis of no oscillation for 7 Be solar neutrinos is inconsistent with our measurement at the 4σ C.L.. Our result is the first direct measurement of the survival probability for solar νe in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of 7 Be, pp, and CNO solar νe, and the limit on the magnetic moment of neutrinos.PACS numbers: 13.35. Hb, 14.60.St, 26.65.+t, 95.55.Vj, 29.40.Mc Neutrino oscillations [1] are the established mechanism to explain the solar neutrino problem, which originated from observations in radiochemical experiments with a sub-MeV threshold [2,3] and from real time observation of high energy neutrinos [4,5]. Neutrino oscillations were also observed in atmospheric neutrinos [4] and have been confirmed with observation of reactorν e [6]. Borexino is the first experiment to report a real-time observation arXiv:0805.3843v2 [astro-ph]

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P. Allegrini and V. Malatesta" EniChem Synthesis, 20097 San Donato Milanese ~ Itat./Three spiro[indoline-naphthoxazines] and a spiro[ind~iine-phenanthroxazine], which exhibit photochromic and thermochromic properties, have been investigated. So vent and structure effects on the absorption spectra of the merocyanines produced under UV irradiation and kine:ic parameters for the ring-closure and ring-opening reactions were studied. Positive solvatochromism was fcund, indicating that the opened form is a weakly polar species. Equilibrium constants and rate constants for the forward and back reactions spiroxazine e merocyanine increase with increasing the solvent polarity and with electron-donating groups in the oxazine moiety. The reaction is endothermic by 10-20 kJ mol-' and almost isoentropic. The activation entropy is generally negative, while the activation Gibbs energy is approximately independent of solvent and structure.Photochromism involving changes in the visible absorption spectrum has attracted much attention in the last decades because of the variety of practical applications of photochromic systems. ' The photochromic properties of the spir ocompounds are well known. Spiropyrans have been extensively studied2 and, more recently. spiroxazines hac t' been the subject of many investigation^.^ I s Interest in these compounds is justified by their high durability with respect to photoexci tation.The photochromism of these molecules is due to photocleavage of the spirobond under UV irradiation to give 'in open merocyanine structure (photomerocyanine) which absorbs in the visible region.General agreement can be found in the literature about some aspects of the mechanistic behaviour of these photochromic systems. It is well known, from experiments uirh picosecond time resolution, that the C-0 bond breakage in the excited state occurs on the picosecond timescale.-' Experimental evidence has been reported for the production of several (at least two') merocyanine isomers in a transoid structure.' Thermal bleaching of the coloured form is knoun to be a relatively slow process (rate constant: 0.01 1Cl However, there are some doubts about the nature of the primary photoproduct 'X', whether it is a non-planar cisoid structure,-or a transoid form undergoing very fast thermd equilibration.' Conflicting results have been reported on the quantum efficiency of the photocolouration reaction, which in some cases differs, for the same molecule, by more than 100°/0.4.5.'3 Large discrepancies can also be found in the molar absorption coefficients of the open forms determined by different method^.^.' 3 * 1 J In this paper we report the effect of the solvent and strubture on the thermal equilibrium between coloured and colourless forms, on the kinetics of thermal bleaching of the photomerocyanines and on their absorption properties. These measurements. which give an overall view of the energetics of these systems, can also give mechanistic information about the thermal breaking and reforming of the spirobond. 1 'L.5.13 1. Ex per ...

A series of derivatives of 5,10,15,20-tetrakis-(4-N-methylpyridyl)-porphine, where one N-methyl group was replaced by a hydrocarbon chain ranging from C6 to C22, were characterized for their photophysical and photosensitizing properties. The absorption and fluorescence features of the various compounds in neutral aqueous solutions were typical of largely monomeric porphyrins, with the exception of the C22 derivative, which appeared to be extensively aggregated. This was confirmed by the very low triplet quantum yield and lifetime of the C22 derivative as compared with 0.2-0.7 quantum yields and 88-167 micros lifetimes for the other porphyrins. The photophysical properties and photosensitizing activity toward N-acetyl-L-tryptophanamide of the C22 porphyrin became comparable to those typical of the other derivatives in 2% aqueous sodium dodecyl sulfate, where the C22 compound is fully monomerized. All the porphyrin derivatives exhibited at micromolar concentrations photoinactivation activity against both Staphylococcus aureus and Escherichia coli, even though the gram-negative bacteria were markedly less photosensitive. The photosensitizing efficiency was influenced by (1) the amount of cell-bound porphyrin, which increased with increasing length of the hydrocarbon chain; and (2) the tendency to undergo partial aggregation in the cell, which seems to be especially important for the C22 derivative.

This work concerns a combined photophysical, photochemical and photobiological study of three drugs (psychotherapeutic agents) of the phenothiazine series: perphenazine, fluphenazine hydrochloride and thioridazine hydrochloride. The excited-state properties were first investigated by stationary and time-resolved fluorimetry and by laser flash photolysis. The spectral description was assisted by quantum-mechanical calculations with the INDO/1-CI method. In organic media the lowest excited singlet state was found to decay by fluorescence (small quantum yield) and mainly by intersystem crossing to the lowest triplet state, which is responsible for oxygen photosensitization (high yields of singlet oxygen production) and photodegradation. A further decay pathway in aqueous solutions was the photoionization process, which led to the formation of the phenothiazine radical cations and the solvated electron. After the preliminary study of the photobehavior in organic solvents and in water, the phototoxicity of the three drugs was investigated on various biological substrates through a series of in vitro assays under UVA irradiation. Photohemolysis of mouse erythrocytes and phototoxicity on cultured murine fibroblasts were observed for all three compounds. Lipid photoperoxidation was then investigated using linoleic acid as the unsaturated lipid model and isolated red blood cell membranes. The drug-induced photodamage was also evaluated on proteins by measuring the photosensitizing cross-linking in erythrocyte ghosts. The combined approach proved to be useful in understanding the mechanism by which these phenothiazine derivatives induce skin photosensitization. In particular, the photophysical properties of the compounds under investigation and the results of the study on their phototoxicity are in agreement with a mechanism that involves the radical cation of the drugs as a main intermediate.