Search results for "PHOTOCHEMISTRY"
showing 10 items of 2034 documents
Photocatalytic coalescence of functionalized gold nanoparticles.
2009
A novel strategy for the synthesis of chromophore-functionalized AuNPs with a narrow size distribution is reported. It consists of increasing the size of preprepared NPs by means of a fast (second scale) and clean (light and an organic photocatalyst) method. The results agree with thiolate ligand liberation from the NP surface promoted by photogenerated radicals. This lets gold cores come together and finally coalesce.
The fragmentation of 5- and 3-substituted thiophene-2-carboxamides under electron impact
1980
The 70 eV electron impact mass spectra of twelve 5- and 3-substituted thiophene-2-carboxamides are discussed with the aid of exact mass measurements and labelling experiments. All mass spectra exhibit pronounced molecular ions. Some isomeric 5- and 3-substituted title compounds can be differentiated by mass spectrometry. The fragmentation is influenced by a strong ‘ortho-effect’ which activates the NH3 elimination. In the other cases the most important fragmentation is NH2˙ loss, followed by CO elimination.
Studies in organic mass spectrometry. Part 17—Formation of phenol radical ions by rearrangement of the molecular ions of someN-arylthiophenecarboxami…
1995
It has been shown by exact mass measurements and collision-induced dissociation mass-analysed ion kinetic energy spectra that the structure of the m/z 124 ion observed in the mass spectra of N-(4-methoxyphenyl)thiophene-2-carboxamide, N-(4-methoxyphenyl)thiophene-3-carboxamide, N-(4-methoxyphenyl)-5-nitrothiophene-3-carboxamide and N-(4-methoxyphenyl)benzamide is identical with that of the molecular ion of 4-methoxyphenol. This ion becomes abundant in metastable energy window reactions. A probable mechanism for its formation is discussed.
Unveiling anion-induced folding in tripodal imidazolium receptors by ion-mobility mass spectrometry.
2021
The anion-induced folding of tripodal imidazolium receptors has been investigated by NMR spectroscopy, electrospray ionization ion mobility mass spectrometry and DFT calculations. Such folding can be switched by anion release upon collision induced dissociation.
The Role of Polyvinylpyrrolidone as a Potential Fluorophore for the Detection of Nitroaromatic Explosives
2022
Background: Detection of explosives (Nitroaromatic compounds) is one of the major issues faced in global security and, to date, remains a challenge even though some materials are developed for their detection. This study introduces the use of polyvinylpyrrolidone (PVP), a nonconjugated conducting polymer, as a potential fluorophore for sensing nitroaromatics. The stimuliresponse of fluorescence of PVP on interaction with energetic nitroaromatics was investigated in the present study. Methods: Fluorescence quenching studies of 5% PVP was carried out by the addition of varying concentration of quenchers (m-dinitrobenzene, trinitrobenzene and 2,4,6-trinitrophenol). To study the effect of diff…
Recent Advances in Photocatalytic Functionalization of Quinoxalin‐2‐ones
2020
Quinoxalin‐2(1H)‐one is an important class of nitrogen heterocycle in medicinal and pharmaceutical industry, which became a synthetic target in organic chemistry in recent years. This review covers the recent advances in the functionalization of this particular nitrogen heterocycle through photocatalysis.
Stability of E' centers induced by 4.7eV laser radiation in SiO2
2007
The kinetics of E' centers (silicon dangling bonds) induced by 4.7eV pulsed laser irradiation in dry fused silica was investigated by in situ optical absorption spectroscopy. The stability of the defects, conditioned by reaction with mobile hydrogen of radiolytic origin, is discussed and compared to results of similar experiments performed on wet fused silica. A portion of E' and hydrogen are most likely generated by laser-induced breaking of Si-H precursors, while an additional fraction of the paramagnetic centers arise from another formation mechanism. Both typologies of E' participate to the reaction with H_2 leading to the post-irradiation decay of the defects. This annealing process is…
Hydrogen-related conversion processes of Ge-related point defects in silica triggered by UV laser irradiation
2005
The conversion processes of Ge-related point defects triggered in amorphous SiO2 by 4.7eV laser exposure were investigated. Our study has focused on the interplay between the (=Ge•-H) H(II) center and the twofold coordinated Ge defect (=Ge••). The former is generated in the post-irradiation stage, while the latter decays both during and after exposure. The post-irradiation decay kinetics of =Ge•• is isolated and found to be anti-correlated to the growth of H(II), at least at short times. From this finding it is suggested that both processes are due to trapping of radiolytic H0 at the diamagnetic defect site. Furthermore, the anti-correlated behavior is preserve…
Optical properties of Ge-oxygen defect center embedded in silica films
2007
The photo-luminescence features of Ge-oxygen defect centers in a 100nm thick Ge-doped silica film on a pure silica substrate were investigated by looking at the emission spectra and time decay detected under synchrotron radiation excitation in the 10-300 K temperature range. This center exhibits two luminescence bands centered at 4.3eV and 3.2eV associated with its de-excitation from singlet (S1) and triplet (T1) states, respectively, that are linked by an intersystem crossing process. The comparison with results obtained from a bulk Ge-doped silica sample evidences that the efficiency of the intersystem crossing rate depends on the properties of the matrix embedding the Ge-oxygen defect ce…
Tuning of the photoinduced charge transfer process in donor-acceptor "double cable" copolymers
2003
The covalent linking of acceptor molecules to electron donating conjugated polymer is an approach for the development of new photoactive materials for the fabrication of organic photoelectric conversion devices. With this strategy we have designed a polyalkylthiophene copolymer series containing in the side chain anthraquinone molecules as electron acceptor. The peculiar features of the copolymers are the good processability and the ease in tailoring the content of acceptor moieties. Their potential use as photoactive materials is investigated in terms of the photoinduced charge transfer properties, studied by FTIR photoinduced absorption and Light Induced Electron Spin Resonance spectrosco…