1,721,036 research outputs found
Lower rim amide (1, 3) functionalised calix [4] arene amido-thiourea derivatives as dimetallic Zn (II) coordination complexes for anion recognition/sensing
No full textA laser flash photolytic study of para-methoxytoluene cation radicals. The effect of -substituents on the proton transfer reactions
No full textAn acridinium-based sensor as a fluorescent photoinduced electron transfer probe for proton detection modulated by anionic micelles
No full textA water-soluble fluorescent pH sensor of 9-amino-10-methylacridinium chromophore with the
2-(diethylamine)ethyl chain as a receptor shows an “off–on” response going from basic to acidic solution.
Photoinduced electron transfer has been directly demonstrated to be the quenching mechanism by the
observation of the long-lived acridinyl radical. The interaction of the protonated sensor with anionic
micelles causes a significant increase in the detection sensitivity of pH
Unusual high fluorescence of two nitro-distyrylbenzene-like compounds induced by CT processes affecting the fluorescence/intersystem-crossing competition
No full textTwo nitro-substituted 1,4-distyrylbenzene-like compounds have been investigated using stationary and time- resolved (ns/fs) spectrometric techniques as a function of solvent polarity. In the two compounds the central benzene ring is substituted with a p-nitrostyryl group at one side while, at the other side, compound 1 (asymmetric) bears a pyrid-4-ylethenyl group and compound 2 (symmetric) another p-nitrostyryl group. The solvent dependent intramolecular charge transfer (ICT) in the singlet manifold was found to strongly affect the competition among fluorescence, intersystem crossing and trans–cis photoisomerization. The presence of nitro-groups in the 1,4-distyrylbenzene skeleton causes the usual strong decrease of fluorescence in favour of intersystem crossing to a reactive triplet state. However, the favoured formation of the ICT state in polar solvents induces an unexpected important increase of the fluorescence quantum yield (three/two order of magnitude for the nitro and dinitro derivatives, respectively). The ultrafast spectral transients helped to understand the solvent effects measured by stationary techniques and gave information on the dynamics of the locally excited singlet state (1LE*) and the 1ICT* state, fast produced in polar solvents. Evidence of dual fluorescence in a limited range of solvent polarity, particularly for compound 1, is also reported. The role of an upper triplet state in a non-polar solvent is discussed also based on quantum- mechanical calculations (TD-DFT method) and temperature effects on the photophysical parameters
Photophysics of cyanophenylpyrroles: Investigation of solvatochromic properties and charge transfer by ultrafast spectroscopy and DFT calculations
No full textA comprehensive investigation of the photophysics of cyanophenylpyrrole derivatives has been carried out by means of steady-state, nanosecond and femtosecond resolved absorption and fluorescence techniques, and quantum-mechanical calculations. This study revealed that the investigated compounds (1-3) are highly fluorescent molecules (Phi(F) = 0.2-0.9) with lifetimes in the range 2-8 ns. The compounds exhibit weak hypsochromic solvatochromic changes in the absorption and large batochromic shifts in the fluorescence spectra. An increase in solvent polarity does not induce a reduction of the fluorescence quantum yields, but causes a lengthening of the fluorescence lifetimes. The density functional theoretical calculations predicted similar energies for S-1 and S-2, probably resulting in the state mixing and IT character of the relaxed S-1 state. Furthermore, the computed dipole moments have been found to be higher in the excited with respect to the ground state, in agreement with the strong solvatochromic properties experimentally observed in the emission spectra. Ultrafast transient absorption measurements indicated the existence of three decay components assigned to the hot Franck-Condon S-1 state that undergoes vibrational cooling (VC, several picoseconds), the species formed by VC undergoing a torsional motion of the C-C bond between the phenyl and the pyrrole ring (several hundreds of picoseconds), and the relaxed S-1 state that decays radiatively (nanoseconds). Indeed, the calculated optimized geometry of 1-3 in the ground state is characterized by a dihedral angle between the pyrrole and phenyl moieties of about 10-25 degrees, whereas the S1 state is predicted to be more planar than S-0. Due to the fast population of the relaxed S-1 states, the typical dual fluorescence reported for N-phenylpyrroles was not observed for 1-3. (C) 2014 Elsevier B.V. All rights reserved
Photoinduced Reduction of Chloranyl with Alkyl- and Thio-aromatics Investigated by Laser Flash Photolysis
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