Improved Measurement of Solar Neutrinos from the Carbon-Nitrogen-Oxygen Cycle by Borexino and Its Implications for the Standard Solar Model.

We present an improved measurement of the carbon-nitrogen-oxygen (CNO) solar neutrino interaction rate at Earth obtained with the complete Borexino Phase-III dataset. The measured rate, R_{CNO}=6.7_{-0.8}^{+2.0} counts/(day×100 tonnes), allows us to exclude the absence of the CNO signal with about 7σ C.L. The correspondent CNO neutrino flux is 6.6_{-0.9}^{+2.0}×10^{8} cm^{-2} s^{-1}, taking into account the neutrino flavor conversion. We use the new CNO measurement to evaluate the C and N abundances in the Sun with respect to the H abundance for the first time with solar neutrinos. Our result of N_{CN}=(5.78_{-1.00}^{+1.86})×10^{-4} displays a ∼2σ tension with the "low-metallicity" spectroscopic photospheric measurements. Furthermore, our result used together with the ^{7}Be and ^{8}B solar neutrino fluxes, also measured by Borexino, permits us to disfavor at 3.1σ C.L. the "low-metallicity" standard solar model B16-AGSS09met as an alternative to the "high-metallicity" standard solar model B16-GS98.

Molecular-based upconversion in homo/heterogeneous liquids and in micro/nanostructured solid materials.

Radiation upconversion can be an elegant and efficient strategy to minimize waste in energy harvesting and storage processes. The upconversion based on triplet-triplet annihilation processes of molecular dyes is a very versatile approach, but it requires a systematic photophysical characterization of the systems to optimize the upconversion yields and develop materials for technological applications. This paper represents an overview of the work carried out in our laboratories for the study and characterization of a molecular dye pair, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(ii) (PtOEP) and 1,3,6,8-tetraphenylpyrene (TPPy), suitable as the sensitizer and emitter, respectively, in a triplet-triplet annihilation based upconversion process. The investigation has been carried out in various media with increasing complexity. First, we used the dye pair to characterize the UC-efficiencies in homogeneous solvents of different viscosities and in oil-in-water microemulsions; then we explored the possibility to achieve upconversion in solid materials, like nanostructured silica matrices and liquid filled microcapsules. The possibility to achieve upconversion emission even in confined and rigid media has been confirmed and can inspire further applications of the process.

A laser flash photolysis study of curcumin in dioxane-water mixtures.

Curcumin [bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione] was studied by means of UV-VIS absorption spectroscopy and nanosecond laser flash photolysis in 1,4-dioxane-water mixtures in a series of dioxane-water volume ratios. The transient characteristics were found to be dependent on the amount of water. In pure dioxane the triplet state of the molecule in its enolic form was detected (lambda(max) = 720 nm, tau = 3.2 micros), whereas upon water addition, the diketo form was found to prevail, because of the perturbation of intramolecular H-bonded structure. This led to hydrogen abstraction from dioxane by curcumin triplet state and the formation of the corresponding ketyl radical (lambda(max) = 490 nm, tau approximately 10 micros). Laser flash photolysis measurements, carried out in solvents of different polarity and proticity (benzene, cyclohexane and various alcohols), allowed the transient assignments to be confirmed, supporting our interpretation.

Laser flash photolysis of diphenylsulfonyldiazomethane: detection of the sulfene and a sulfene-pyridine ylide

The photochemistry of diphenylsulfonyldiazomethane (DSD) was studied by means of nanosecond laser flash photolysis. The photochemical behavior of this molecule upon UV irradiation is characterized by sulfene formation, presumed to arise via Wolff rearrangement of a carbene. We were able to detect the sulfene and the sulfene ylide formed upon sulfene trapping by pyridine. Sulfene quenching by nucleophiles was also examined.

Laser flash photolysis of 2-diazo-1,3-diphenyl-1,3-propanedione: An unusual long-lived triplet as a reaction intermediate

Laser flash photolysis of 2-diazo-1,3-diphenyl-1,3-propanedione (DBD) is presumed to involve a short-lived carbene, followed by Wolff rearrangement to a long-lived ketene. We have detected ketene ylides following photolysis of DBD in the presence of amines but not with pyridine. The triplet state of DBD lives several microseconds, an unusual observation for a diazo compound; however, the triplet is not a ketene precursor, which must result from excited singlet state fragmentation of DBD.