Energy transfer quenching reaction

The rates and chemiluminescent intensities of atom-transfer reactions are proportional to the concentrations of the reactants, but the intensity is inversely proportional to the concentration of inert gas present. The latter quenches the excited state through coUision with an efficiency dependent on the stmcture of the inert gas. Chemiluminescence Qc increases with temperature, indicating that excitation has a higher activation energy than the ground state... 

Taylor and Jarman [1] observed SL spectra in the range of 280-740 nm from 2 M NaCl solutions saturated with argon, krypton and xenon sonicated at frequencies of 16 and 500 kHz. The spectra showed a continuum background with bands at about 310 nm and a peak of sodium D line, which exhibited appreciable asymmetric broadening, as shown in Fig. 13.2. The bands around 310 nm result from the A2L+ — X2n transition of OH radicals. The OH bands are quenched in salt solutions compared with those in water, which suggests the energy transfer reaction... 

Bimolecular reactions with paramagnetic species, heavy atoms, some molecules, compounds, or quantum dots refer to the first group (1). The second group (2) includes electron transfer reactions, exciplex and excimer formations, and proton transfer. To the last group (3), we ascribe the reactions, in which quenching of fluorescence occurs due to radiative and nonradiative transfer of excitation energy from the fluorescent donor to another particle - energy acceptor. 

Quenching is the reduction in fluorescence intensity and can be caused by various processes. It occurs either during the lifetime of the excited state or in the ground state. Quenching processes that happen in the excited state are collisional quenching, charge transfer reactions, or energy transfer. The latter is the basis for FRET probes but the other events happen as well under certain conditions and it is important to consider them. 

In the scheme, the assumption is made that the only important quenching event is electron transfer and that energy transfer quenching is negligible. The series of electron transfer events in the scheme are initiated by optical excitation to give the excited state and the electron transfer reactions which occur fol-... 

A.J. Bard, University of Texas The fact that one can generate chemiluminescence in polymer films containing Ru-(bpy)3 2 implies that the excited state may not be quenched completely by electron transfer reactions. Are the photoreactions you describe thermodynamically uphill (i.e., with chemical storage or radiant energy) or are they photocatalytic ... 

Quantum yields, free energy changes, — AG°, for the electron transfer reaction from the P fragment to the Q fragment of P-L Q molecules in methylene chloride solution [55]... 

The efficiency of luminescence quenching (see Table 1) was found to correlate with the change in the free energy, — AG°, of the electron transfer reaction estimated according to the formula (see Chap. 7, Sect. 4.2)... 

Quenching.—Any deactivation of an excited state (but not necessarily to the ground state) by interaction with other components of the system, which prevents some otherwise observable process such as emission or chemical reaction. Energy transfer is always involved but the detailed mechanisms may vary considerably. 

Upon laser flash photolysis of a cyclohexane solution containing DTT and DNB, no transient absorption band ascribable to the products of electron-transfer reactions was observed. The transient absorption due to t(326) disappeared within 500 ns after laser excitation, and a new absorption band appeared at wavelengths <350 nm. The new band can be attributed to the triplet excited state of DNB. The result indicates that t(326) is quenched by energy transfer to DNB. The decay rate constant of t(326) for the energy transfer was estimated to be 8.8 x 109 M 1 s. As for cyclohexane solution of 327 and DNB, quenching of T(327) by energy transfer was also observed and the rate constant was 1.1 x 1010 M-1 s... 

Bimolecular quenching of the excited states of metal complexes generally involves electron transfer or energy transfer processes ( 1). Recently, however, Pt2(pop)4 " has been found to undergo a photochemical reaction involving atom abstraction as a primary photoprocess (.26). The reaction involves the catalytic conversion of isopropanol to acetone ... 

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