Magnetic field effects triplet emission

A number of techniques have been applied to probe the details of the ECL processes. Triplet intermediates resulting from the redox reaction have been identified by interception with fnms-stilbene and determination of the extent of trans- to cis-isomerization (Freed and Faulkner, 1971) as well as by observing the effect of an external magnetic field on the emission intensity (Faulkner et al., 1972 Tachikawa and Bard, 1974). In the latter studies, it was shown that a magnetic field decreases the rate of the triplet-triplet annihilation reaction, (112) or (114), and also the rate of quenching of triplets by radical ions [eqn (116)]. Since the rate of the radical ion redox... 

From the Stem-Volmer plots, Matsuzaki and Nagakura found the collision-free lifetime to become shorter in the presence of a magnetic field and they explained the reduction in fluorescence lifetime and the decrease in fluorescence intensity by an enhancement of ISC (due to the perturbation of the excited singlet state by triplet states). The influence of the magnetic field on the emission spectrum, which consists of a banded structure and a continuum, has not been examined and hence the magnetic effect on the continuum emission is unknown. 

An external magnetic field was observed to have practically no effect on the intensity of the thianthrene (430 nm) emission, indicating that no triplet states are involved. The shorter-wavelength emission of the oxadiazole 102, however, is probably due to a triplet-triplet annihilation reaction of diphenyloxadiazole triplets. These are produced in the radical-ion reaction between 101 and 102, yielding thianthrene excited-singlet molecules and diphenyl-oxadiazole excited-triplet molecules ... 

Electron Spin Resonance Electron spin resonance measures the effect of micro-waves on a molecule with spin (usually a free radical or triplet) in a magnetic field. The detection can be either through the absorption of microwave energy (conventional ESR) or the effect of a microwave frequency on the emission of light (Fluorescence Detected Magnetic Resonance FDMR). Because the transition energy of the electron in a molecule depends on the interaction of that electron with much of the molecule, spectra have many lines and contain substantial information about the structure of the species being studied. 

The lifetimes of these bands at 1.4 K are 77 ps and 62 ps, respectively, which corresponds in each case to an emissive triplet state. The possible assignments for the lowest triplet state are Eu from dxz, dyz cg), A2u from d (ai ), and from dxy (feig). The application of a magnetic field causes a shortening in the Ufetime of both excited states, with the effect being greatest when the field is applied along the Tl-Pt molecular axis. 

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