Luminescence dissymmetry ratio

In circularly polarized luminescence spectroscopy, one normally reports the ratio of Al to the total intensity 7. The results are most often reported in terms of the luminescence dissymmetry ratio, glum, which is defined as the ratio of the differential emission intensity to the average total emission intensity.75... 

Luminescence dissymmetry ratio values (glum) the spectral range of the D4 transition for 0.01 M... 

We thus define the luminescence dissymmetry ratio, as follows ... 

A = absorbance c = concentration d = path length / = frequency 1,5 = absorption dissymmetry ratio glujjj = luminescence dissymmetry ratio I = light intensity J = total angular quantum number t = time = extinction coefficient A = wavelength a = standard deviation. 

Because of the difficulty in measuring absolute emission intensities, it is common to report the degree of CPL in terms of the luminescence dissymmetry ratio (or factor)... 

Under the assumptions that the hneshapes for CPL and total luminescence are identical (this is appropriate for the usually sharp isolated pure electronic transitions that are often target of CPL measurements), and that the number of molecules in the emitting state is independent of their orientation, the luminescence dissymmetry ratio can then be related to the molecular... 

Because of the difficulty in measuring absolute emission intensities, in CPL spectroscopy one commonly reports the ratio of AI(X) to the total intensity I(X). This ratio, glum(X), is referred to as the luminescence (or emission) dissymmetry ratio, and is explicitly defined at wavelength, X, as... 

The Pfeiffer effect, the outer-sphere interaction of a chiral substrate with a rapidly interconverting racemic solution of a chiral lanthanide complex, can be investigated by measurement of the luminescence dissymmetry factor (the ratio of circularly polarized luminescence to total luminescence) for Eu or Tb " complexes. Thus the racemic D chiral complexes [M(dpa)3], where M = Eu or Tb, interact in an outer-sphere manner with the following optically active spiecies cationic chiral transition metal complexes, ascorbic acid, aminocarboxylates, tartrates, amines and phenols. Association constants can be obtained from limiting values of the dissymmetry factors. In some cases, inner-sphere complexation can be demonstrated, as judged by changes in the general nature of the circularly polarized luminescence spectrum and pH irreversibility of the complexation. 

Absorption (gabs) luminescence (gium) dissymmetry ratios for selected transitions of a chiral crystal of... 

For the simple model enantiopure systems described above, it was concluded that the time dependence of the CPL and total luminescence were identical, and, therefore, the dissymmetry ratio contained no dynamic molecular information. This, of course, would not be the case if intramolecular geometry changes, that would effect the chirality of the molecular transitions, were occurring on the same time scale as emission. However, no such examples of this type of study have yet appeared. Time-resolved CPL measurements have been useful in the study of racemic mixtures of lanthanide complexes in which racemi-zation or excited state quenching is occurring on the same time scale as emission. 

Measurement of CPL from racemic mixtures is not a technique that can be applied to all racemic solutions. For moderately luminescence systems values of approximately 10 are measurable. This means that the intrinsic absorption and emission dissymmetry ratios need to be on the order of 10 for this experiment to be successful. Although there have been a couple of examples using this technique in organic systems, by far the most widely studied systems are racemic lanthanide complexes, such as given in Figure 5, because of the large and g bs values that may exist for certain f o f transitions. It is also useful to perform these experiments in a time-resolved mode and as a function of temperature to determine racemization rate constants. 

The experimental determination of the emission intensity in absolute units is quite complex as it commonly happens in luminescence measurements, /(A) and A/(A) are often measured in arbitrary units, which are dependent on the equipment and the experimental conditions adopted. The dissymmetry factor gem(- ) is a significant quantity because it is a ratio of emission intensities and is therefore unaffected by the instrumental and experimental parameters. Its value gives an absolute quantification of the chirality of the emitting excited state. 

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