Circular polarized luminescence CPL

Circular polarized luminescence (CPL) is not covered in this book because the field of application of this phenomenon is limited to chiral systems that emit different amounts of left and right circularly polarized light. Nevertheless, it is worth mentioning that... 

Circularly polarized luminescence (CPL) from chiral molecular systems is the emission analog of circular dichroism (CD) and as such reflects the chirality of the excited state in the same maimer as CD probes reflect the chirality of the ground state (Riehl and Muller, 2005). For lanthanide ions, laige CPL (and/or CD) signals are expected for f-f transitions obeying magnetic dipole selection rules, in particular A J = 0, 1 Eu(5Do —> 7Fi), Tb(5D4 7F4, 5D4 7F5), Dy(4F9/2 6Hn/2), Yb(2Fs/2 2F7/2) emissions are typical examples. Recent... 

Figure 14 shows another example the absorption, emission, ECD, and the emission counterpart of ECD - circular polarized luminescence (CPL) - for the lowest energy excitation of <7-camphorquinone. from a recent TDDFT study... 

The J sublevels of rare earths are split by ligand fields of low symmetry. These splittings may be observed in circularly polarized luminescence (CPL) but not in the fluorescence spectrum. Hence CPL spectra provide information on the rare earth ion and thus throw light on the binding site. The emission and CPL spectra of Tb3+ bound to transferrin and cobalbumin were found to be similar leading to the conclusion that the structure and... 

Similarities between CD and absorbance methods are also found between CD and fluorescence and CD and circularly polarized luminescence (CPL). Three prerequisites are needed to produce FDCD and CPL activities. Intense emission signals normally associated with fluorescence are attractive because limits of detection are lowered considerably. FDCD finds more uses as a chromatographic detection device. A CD signal is usually induced by some kind of molecular complexation reaction. Association can be with a simple molecule or with an aggregate of molecules, such as chiral micelles, which are known to be fluorescence enhancers. In cases of color induction combined with fluorescence induction, FDCD can lead to even higher levels of selectivity among analytes that have been derivatized by the same color reagent. 

It is, however, possible to measure chiroptical properties related to the excited states of molecules - circularly polarized luminescence (CPL) [13]. In this case, the sample is excited by unpolarized radiation and the luminescence signal is analyzed by a circular analyzer. Several variants of this concept have been developed, but the applications are targeted more on electronic structure of the excited states of molecules than to their geometries. 

Complexes of lactic acid with a wide variety of metal ions are known and their stability constants have been determined. A variety of techniques has been used in the study of the species formed in the solutions of this hydroxy acid and inorganic ions. Electrochemical and spectrophoto-metric methods have been used with the main aim of determining stability constants of the complex ions. CD and optical rotatory dispersion (ORD) have also proved to be powerful methods in studying, for instance, Mo, Mo , Cu" and Co", as well as lanthanide complexes. Very recently, Brittain et used circularly polarized luminescence (CPL) techniques in the study... 

Europium, and to a lesser extent terbium, complexes of /3-diketones have been studied in solution and in the solid state by means of their fluorescence (luminescence) spectra. As explained further in Section 39.2.10, it is possible to relate the splitting of the Do—> F transitions of Eu " to the symmetry of the emitting complex, and studies of circularly polarized luminescence (CPL) spectra can give related information. Thus a study of EuCls and complexes of Eu with hexafluoroacetylacetone and four other /8-diketones in methanol or DMF showed that while EUCI3 itself had axial symmetry in solution, the complexes had orthorhombic symmetry. The emission spectra of solutions of adducts of Eu(dpm)3 with PhsPO or borneol have been studied at low temperatures where conformal lability is reduced the Ph3PO adduct has uniaxial symmetry but the bulky, less symmetrical bomeol molecule confers lower symmetry on its adducts. ... 

Chiroptical luminescence Circular polarized luminescence (CPL) allows obtaining information about excited state structures. Corresponding achiral information can be obtained from electrochromic phenomena of molecules. Serious experimental problems, which often lead to more artifacts than acceptable, have prohibited a broad application of this method. Information can be obtained about S T transitions of enones and ketones. For metal complexes kinetic studies about stereochemical dynamics are available. New experimental developments seem necessary for a broad application of the CPL. 

Lanthanide f-f transitions are, in principal, more useful than their transition metal counterparts in probing the geometry round the metal ion. In particular the circularly polarized luminescence (CPL) spectra of Eu and Tb has been extensively used for this purpose. However, our understanding of f-f CD/CPL is less than that of d-d transitions. In both the lanthanide ions mentioned above there are sources of both magnetic and electric dipole intensity. The problem is that the transitions belong to different J states and J is, to a first approximation, a good quantum number. To exemplify the transition of Eu is magnetic dipole allowed, the 4 and... 

A number of lanthanide complexes have been shown to exhibit circularly polarized luminescence (CPL—the differential spontaneous emission of left- and right-circularly polarized light). In the absence of any externally applied fields, CPL is exhibited only by systems that have net chirality in their structures or are subject to chiral perturbations by their environment. CPL exhibited by the Af-Af transitions of chiral lanthanide systems provides a sensitive probe of coordination and structure in solution. Applications are limited to systems which possess some element of chirality, but in many cases this merely requires that > 1 ligand of interest has a chiral atom or carries a chiral label (such as a chiral substituent group). ... 

A special case of photo-initiated measurements is provided through chiroptical methods including circular dichroism (CD), optical rotary dispersion (ORD), and circularly polarized luminescence (CPL), whose experimental details are... 

The other key point is that the recognition event should then produce differences in the fluorescence properties of the sensor molecule in the presence of the two enantiomers of the analyte. Several mechanisms can be used to generate the fluorescence response (Figs. 2 and 11) by changing the electronic properties and the conformation of the sensor. Aggregation induced emission enhancement (AIEE) [49] was recently shown to be able to generate an enantioselective fluorescence response. Special optical techniques such as circularly polarized luminescence (CPL) are now available to detect enantioselective interactions occurring in the excited state or in the second coordination-sphere interactions [49]. 

The differential emission of left and right circularly polarized light from luminescent molecular systems is called circularly polarized luminescence (CPL), and is at the basis of the corresponding spectroscopic technique (CPL spectroscopy) [23-25]. CPL spectroscopy should not be confused with fluorescence detected circular dichroism (see Sect. 6.1.6) in the latter technique the differential absorption of the circularly polarized components is detected through fluorescence measurements, owing to the different extent of photoexcitation that left- and right-handed light can produce on a chiral molecule. 

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