Search results for "SINGLET"
showing 10 items of 352 documents
Chemi- and Bioluminescence of Cyclic Peroxides
2018
Bioluminescence is a phenomenon that has fascinated mankind for centuries. Today the phenomenon and its sibling, chemiluminescence, have impacted society with a number of useful applications in fields like analytical chemistry and medicine, just to mention two. In this review, a molecular-orbital perspective is adopted to explain the chemistry behind chemiexcitation in both chemi- and bioluminescence. First, the uncatalyzed thermal dissociation of 1,2-dioxetane is presented and analyzed to explain, for example, the preference for triplet excited product states and increased yield with larger nonreactive substituents. The catalyzed fragmentation reaction and related details are then exemplif…
A Functionalized Noncovalent Macrocyclic Multiporphyrin Assembly from a Dizinc(II) Bis-Porphyrin Receptor and a Free-Base Dipyridylporphyrin
2003
The bis-porphyrin system ZnP 2 , in which two zinc porphyrins are connected by a phenanthroline linker in an oblique fashion, acts as a bifunctional receptor towards the complexation of free-base meso-5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin (4'-cisDPyP). In solution, NMR spectroscopy evidenced quantitative formation of the tris-porphyrin macrocyclic assembly ZnP 2 (4'-cisDPyP), in which the two fragments are held together by two axial 4'-N(pyridyl)-Zn interactions. The remarkable stability of the edifice (an association constant of about 6 x 10 8 M - 1 was determined by UV/Vis absorption and emission titration experiments in toluene) is due to the almost perfect geometrical match betwe…
Complete basis set B3LYP NMR calculations of CDCl3solvent's water fine spectral details
2008
The assignment of singlet at 1.55 ppm and the 1:1:1 triplet at 1.519 ppm to H2O and HOD in the 400 MHz 1H NMR spectrum of CDCl3 solvent were supported by complete basis set (CBS) GIAO-B3LYP calculated chemical shift and the CBS B3LYP estimated 2J(D,H) spin–spin coupling constant (SSCC). The CBS fitting of B3LYP/cc-pCVxZ and B3LYP/pcJ-n predicted SSCC values, the accurate value of 2J(D,H) = − 1.082 ± 0.030 Hz of HOD in chloroform-d1 and the H/D isotopic shift of 0.0307(1) ppm were reported for the first time. The agreement between CBS B3LYP predicted chemical shift, spin–spin values and experiment was good. Copyright © 2008 John Wiley & Sons, Ltd.
Exposure to elevated temperatures and risk of preterm birth in Valencia, Spain
2014
Abstract Background Prematurity is the second-leading cause of death in children under the age of 5 worldwide. It is predicted that the future climate will have more intense, longer lasting and frequent extreme heat episodes, and so the temperature effect on the risk of preterm birth is generating considerable interest in the public health field. Our aim was to explore the potential short-term effects of elevated temperatures on the risk of preterm birth in Valencia (Spain). Methods All singleton natural births born in the metropolitan area of Valencia during the warm season (May–September, 2006–2010) were included ( N =20,148). We applied time-series quasi-Poisson generalized additive mode…
Hyperchargeless triplet Majoron model.
1989
We study the general conditions to maintain the scale of the lepton-number-breaking vacuum expectation value at the electroweak scale. It is shown that the only possibilities are if the main component of the resulting Majoron is a hyperchargeless complex triplet or a neutral singlet. Models with a hyperchargeless triplet, even though phenomenologically more interesting, seem to be very difficult to build because they like to break charge conservation. However, we have found a particular extension, by adding an additional neutral singlet, that solves this problem. The model can give a Majorana mass to the neutrinos in the eV range, ..mu -->..e..gamma.. can proceed with branching ratios at th…
Photocatalytic partial oxidation of limonene to 1,2 limonene oxide
2018
The silylation of crystalline TiO2 P25, commonly used for photocatalytic degradation of pollutants, results in an exceptionally selective catalyst for the aerobic limonene epoxidation to 1,2-limonene oxide under solar light irradiation. The hypothesized mechanism involves the singlet oxygen generated through energy transfer from the excited TiO2 to adsorbed O2 molecules. The reaction product is the valued precursor of bio-based poly(limonene carbonate), a thermoplastic polymer of superior thermal and optical properties whose industrial production is in need of an efficient green synthesis of limonene oxide.
Oxygen and vacancy defects in silicon. A quantum mechanical characterization through the IR and Raman spectra.
2021
The Infrared (IR) and Raman spectra of various defects in silicon, containing both oxygen atoms (in the interstitial position, Oi) and a vacancy, are computed at the quantum mechanical level by using a periodic supercell approach based on a hybrid functional (B3LYP), an all-electron Gaussian-type basis set, and the Crystal code. The first of these defects is VO: the oxygen atom, twofold coordinated, saturates the unpaired electrons of two of the four carbon atoms on first neighbors of the vacancy. The two remaining unpaired electrons on the first neighbors of the vacancy can combine to give a triplet (Sz = 1) or a singlet (Sz = 0) state; both states are investigated for the neutral form of …
Dynamics of Singlet Oxygen Molecule Trapped in Silica Glass Studied by Luminescence Polarization Anisotropy and Density Functional Theory
2020
The support from M-ERANET project “MyND” is acknowledged. A.A., M.M-S., and L.R. were supported by the Research Council of Lithuania (Grant M-ERA.NET-1/2015). The authors thank A. Pasquarello for providing the structures of the amorphous SiO 2 matrix for our computational work and K. Kajihara (Tokyo Metropolitan University) for valuable advice in PL kinetics measurements.
CEMS Study of 57Fe Implanted in Diamond
2002
Conversion electron Mossbauer (CEMS) measurements have been made on a diamond sample implanted with 70 keV 57Fe to a dose of 5 × 1014 cm−2. CEMS spectra were collected in the as-implanted state and after annealing the diamond up to 1470 K. The lower temperature spectra were consistently fitted with three symmetric doublets. With annealing the areal fractions of two of the doublets increased to 44% and 48 %, respectively, while that of the third doublet decreased to be replaced by a single line component with isomer shift δ = 0.0 mm/s. Comparison of the observed isomer shifts with recent in-beam Mossbauer measurements and theoretical calculations allow us to attribute the singlet to intersti…
Torsional Bias as a Strategy To Tune Singlet–Triplet Gaps in Organic Diradicals
2018
Quinoidal compounds with proaromatic structures possess differing degrees of diradical character, where the open-shell diradical resonance form has restored aromaticity throughout the compound. Methods to tune the diradical character of these compounds have traditionally focused on altering the length and the molecular composition of the π-conjugated backbones. However, other molecular design strategies to tune the singlet–triplet gap of π-conjugated quinoidal molecules have not been extensively explored. We previously reported a strikingly small energy gap between the quinoidal and diradical states of a quinoidal small molecule containing methano[10]annulene (TMTQ) that was dictated in lar…