The magnetic-field dependence of the cage escape efficiency ( ce ) of [Ru(bpy) 3 ] 3+ and methyl viologen radicals (MV +• ) from the primary redox pair formed upon quenching of photoexcited [Ru(bpy) 3 ] 2+ by MV 2+ was measured by laser flash spectroscopy in aqueous solution as a function of the magnetic field (0-2.85 T) in the temperature range from 5 to 69°C. Furthermore, the 1 H NMR T 1 times of the paramagnetic [Ru(bpy) 3 ] 3+ were measured between -40 and 42°C. The kinetic data were analyzed in terms of a kinetic model that takes into account spin conservation in the forward reaction between the 3 MLCT state of [Ru(bpy) 3 ] 2+ and the electron acceptor MV 2+ yielding a triplet spin-correlated radical pair (RP) and the in-cage backward electron transfer requiring singlet character of the RP. The triplet-to-singlet spin conversion of the geminate RP is explicitly treated by the stochastic Liouville equation formalism. By theoretical simulation of the observed magnetic field dependence of ce , the temperature dependent absolute values of the rate constants k ce (cage escape), k bet (backward electron transfer in singlet RPs), and k TS (magnetic-field independent triplet-to-singlet interconversion) could be assessed. The temperature dependence of k ce exhibits a very good proportionality to the solvent viscosity. The values obtained for k TS are in good agreement with the results on the electron spin relaxation time of [Ru(bpy) 3 ] 3+ derived by the Solomon relation from the 1 H NMR T 1 times. The effective rate of backward electron transfer in the geminate RP turns out to be close to spin-controlled, i.e., it is determined by the rate constant k TS of the triplet-singlet spin conversion process. The true rate constant k bet , varying from 5.5 × 10 10 s -1 to 1.2 × 10 11 s -1 , is about seven times larger than the effective value for the total backward electron transfer comprising spin conversion and spin-allowed backward electron transfer.

Cu(II) mediated low density lipoprotein (LDL) oxidation has been followed by the changes in absorbance at 234 nm and the emitted low level chemiluminescence (CL). The similarity of the time profiles allows us to conclude that the emitted CL is due to the decomposition of a transient product, most likely a hydroperoxide. Red wine, as well as its fractions, afford a noticeable protection when added prior to the start of the LDL oxidation process. On the other hand, when they are added after the onset of the autocatalytic oxidation phase, red wine and its fractions behave as pro-oxidants. This is particularly evidenced by a strong burst of CL (enhancement of the light by a factor approximately 20). This burst is reduced by metal chelators (EDTA and DFO) and can be associated to a sequence of reactions such as XOH + Cu(II) --> X* + H(+) + Cu(I), Cu(I) + LOOH --> chemiluminescence where XOH is a phenolic compound and LOOH is a peroxide-like compound produced in the LDL oxidation.

The influence of ionic strength variation and of exciplex formation between silver ions and triplet excited RuL

In practical sensor applications it is advantageous for the sensor material to be a solid. Yet, even for the simplest intramolecular processes, where no bonds are broken or formed, reactions are generally different in fluids than in solids. For example, in the case of photoexcitation of a molecule and its return to the ground state, the rates of the processes are strongly dependent on the medium's chemical composition and physical state. 1-3 Sometimes it would be desirable for a material to have macroscopic properties of a solid and nanoscopic (and thus chemical) properties of a fluid. This latter case is the subject of this report. Developing new materials to detect small magnetic fields (MF) (<100 mT) could serve to impact magnetic data storage processes. 4-8 Nonincremental improvements will likely require new paradigms such as shifting from electronic to optical-based sensing of magnetized domains. The potential advantages of electrooptical systems over purely electrical systems have been much touted. 9-12 To date, however, very limited efforts have been directed at finding materials that respond optically to weak MFs. 13 As suggested above, aside from other considerations, a practical MF sensor would require fabrication from solids.