Search results for "quench"
showing 10 items of 306 documents
Assemblies of semiconductor quantum dots and light-harvesting-complex II
2010
Abstract A novel hybrid system composed of fluorescent core/shell semiconductor quantum dots and the light harvesting complex II (LHCIIb), a membrane protein of higher plants, has been assembled. Experiments with different mutants show that hybrid formation can be mediated by a C-terminal His 6 tag attached to the protein as well as by positive charges of the first N-terminal amino acids of LHCIIb. Quenching of the quantum dot fluorescence upon binding of LHCIIb was partially attributed to energy transfer from the quantum dots to LHCIIb.
The Role of Site-Specific Hydrogen Bonding Interactions in the Solvation Dynamics of N-Acetyltryptophanamide
2012
Measurements of the ultrafast broadband UV fluorescence of N-acetyltryptophanamide (NATA) provide detailed information on its relaxation patterns in three different solvents: methanol (MeOH), water and acetonitrile (ACN). Several processes leading to excited state solvation and cooling are found to occur on different characteristic time scales and are thoroughly analyzed. Comparison between protic MeOH and aprotic ACN allows one to single out a 12 Ps component in the former, which is attributed to the rearrangement of H-bonds existing between the protic solvent and excited NATA. This significantly stabilizes the excited state and provides the molecule with an efficient cooling mechanism. Th…
Kinetic solvent effects on the reaction of an aromatic ketone pi,pi* triplet with phenol. rate-retarding and rate-accelerating effects of hydrogen-bo…
2007
Quenching of the 2-benzoylthiophene π,π* triplet, 3BT*, by phenol yields the corresponding ketyl and phenoxyl radicals. Reaction rates were measured in 10 solvents having a range of hydrogen-bond acceptor strengths (β2H values). There appear to be two mechanisms: (i) a bimolecular reaction of 3BT* with “free” (i.e., not H-bonded) phenol in which the 3BT* accepts both a proton and an electron from the phenol, the rate decreasing as β2H increases; (ii) a trimolecular reaction of 3BT* with phenol that is H-bonded to a solvent molecule, PhO−H···S, in which the proton goes to the S and the electron to the 3BT*, the rate increasing as β2H increases.
Spontaneous lifetimes and relaxation cross-sections of the D1Π state of NaRb
2003
Abstract The time-resolved intensity of dispersed laser induced fluorescence following the Ar + -laser D 1 Π←X 1 Σ + excitation was measured for both 23 Na 85 Rb and 23 Na 87 Rb isotopomers in a thermal cell. Spontaneous radiative lifetime values determined for v ′ ( J ′ ) rovibronic levels of the D 1 Π state in the v ′ range from 0 to 17 and J ′ from 8 to 131 varied from 22.5 to 17.3 ns. Averaged collisional quenching cross-section values of (3–6)×10 −14 cm 2 were obtained for NaRb (D 1 Π, v ′ , J ′ ) + Rb collisions from the Stern–Volmer plots.
Covalent and non-covalent coupling of a Au102 nanocluster with a fluorophore: energy transfer, quenching and intracellular pH sensing
2021
Interactions between an atomically precise gold nanocluster Au102(p-MBA)44 (p-MBA = para mercaptobenzoic acid) and a fluorescent organic dye molecule (KU, azadioxatriangulenium) are studied. In solution, the constituents form spontaneously a weakly bound complex leading to quenching of fluorescence of the KU dye via energy transfer. The KU can be separated from the complex by lowering pH, leading to recovery of fluorescence, which forms a basis for an optical reversible pH sensor. However, the sensor is not a stable entity, which could be delivered inside cells. For this purpose, a covalently bound hybrid is synthesized by linking the KU dye to the ligand layer of the cluster via an ester b…
Rotational quenching of monodeuterated water by hydrogen molecules
2011
Cross sections and rate coefficients for low lying rotational transitions in HDO induced by para and ortho-H(2) collisions are presented for the first time. Calculations have been performed at the close-coupling and coupled-states levels with the deuterated variant of the H(2)O-H(2) interaction potential of Valiron et al. [J. Chem. Phys., 2008, 129, 134306]. Rate coefficients are presented for temperatures between 5 and 100 K and are compared to the corresponding rates for H(2)O and D(2)O. Significant differences caused by the isotopic substitution, in particular the C(2v) symmetry breaking, are observed. Finally, our rates are found to be significantly larger (by up to three orders of magn…
Photochemistry of 3,6-bis(styryl)pyridazines in solution and in neat liquid crystalline phase—optical switching and imaging techniques
2008
Abstract 3,6-Bis(styryl)pyridazines 1a – f with 2–6 alkoxy groups show on irradiation in solution a stereoisomerization which leads to a photostationary state of ( E , E )- and ( E , Z )-isomer. Sensitizing and quenching experiments reveal that the ( E , E )→( E , Z ) route is a pure triplet process, whereas the ( E , Z )→( E , E ) route can have a minor singlet by-reaction. Hexyloxy or dodecyloxy chains on the terminal benzene rings convey the ( E , E )-isomers of compounds 1a , b , d – f thermotropic liquid crystalline properties. In particular S A , S C , and S F/I phases were studied with regard to their photochemical behavior. Depending on the system, photodegradation of the smectic ph…
Oligophenylenevinylenes in Spatially Confined Nanochannels: Monitoring Intermolecular Interactions by UV/Vis and Raman Spectroscopy
2008
Perhydrotriphenylene-based channel-forming inclusion compounds (ICs) and thin films made of polyphenylenevinylene (PPV)-type oligomers with terminal alkoxy groups are investigated and compared in a combined experimental and theoretical approach. Interchromophore interactions and host-guest interactions are elucidated by UV/Vis and Raman spectroscopy. The impact of the local environment of the chromophore on the optical and photophysical properties is discussed in light of quantum-chemical calculations. In stark contrast to thin films where preferential side-by-side orientation leads to quenching of photoluminescence (PL) via non-emissive traps, the ICs are found to be attractive materials f…
Sensitive laser spectroscopy on trapped barium ions by quenching with hydrogen
1983
The sensitivity of laser spectroscopy on barium ions stored in a radio frequency quadrupole trap was drastically increased by using hydrogen for quenching the optically pumped metastable states. The attained fluorescence intensity per ion permits the detection of single ions. The method will be applied to environmental studies on actinides.
Molecular quenching and relaxation in a plasmonic tunable system
2008
Molecular fluorescence decay is significantly modified when the emitting molecule is located near a plasmonic structure. When the lateral sizes of such structures are reduced to nanometer-scale cross sections, they can be used to accurately control and amplify the emission rate. In this Rapid Communication, we extend Green's dyadic method to quantitatively investigate both radiative and nonradiative decay channels experienced by a single fluorescent molecule confined in an adjustable dielectric-metal nanogap. The technique produces data in excellent agreement with current experimental work.