CPL spectra

CPL spectroscopy may also be used to signal the nature of the ternary anion adduct. In the series of phospho-anion complexes of [Eu.la]3+, Figure 5, complexes of HP042 and glucose-6-phosphate give identical CPL spectra - consistent with their very similar NMR spectral profile. Adducts with phospho-tyrosine, N-acetyl phospho-Tyr and a short peptide (phosphorylated at the Pyr residue) are also near-identical, consistent with chemoselective binding of the Tyr-OP phospho-anion. 

Further studies reported similar CPL spectra for [Yb(28a)]3+, as compared to [Yb(28b)]3+ (Dickins et al., 1999), with dissymmetry factor gium for the peak corresponding to the maximum of luminescence (at 995 nm) of —0.18 (Maupin et al., 2000). A quantitative comparison with the CD spectrum for which the absorption dissymmetry factor gabs = —0.11 is difficult in view of the spectral overlap of various transitions from differently populated LF sub-levels, as demonstrated in a previously cited study (Di Bari et al., 2000a). However, such a comparison is useful to verily the sign of the CPL emission ... 

Furthermore, using the procedure described above, one obtains the following results ga s(457.9 nm)= -0.086, ga s(450.9 nm)= -0.41, and gjl n(664.5 nm) = -0.046. The identity of the specific enantiomer in excess (in this case the A enantiomer) has been determined by comparison of CPL spectra for a similarly perturbed EulDPA S- species and the solid state CPL and CD of A-Eu(ODA>33- [54,55]. The most difficult measurement of the three given above is the CD of the lanthanide complex at the excitation wavelength. This is due to the fact that the extinction... 

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... 

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. ... 

The di-LCPAs in solution and in cast film showed monosignate and bisignate Cotton effects in their CD spectra, respectively. These results suggest the formation of intrachain and interchain helical structures, respectively. In spite of this, the di-LCPAs in solution and in cast film exhibited no CPL [21]. However, (/f)-/(S)-Poly-4 in an N -LC film showed bisignate CPL bands centered around the PL emission band (Fig. 11.12a). (/f)-Poly-4 exhibited positive and negative CPL bands at wavelengths shorter and longer than 530 nm, respectively. (S)-Poly-4 exhibited CPL bands with handedness opposite to those (/ )-Poly-4. The CPL spectra of (/ )-/(S)-Poly-4 in an N -LC film showed gem values of 1.8 x 10 and... 

Fig. 11.12 PL upper), CPL spectra middle), and gem lower) spectra of a (/f)-/(S)-Poly-4 N -LC film, and b (/ )-/(S)-Dl doped (reic)-Poly-4 (10 wt %) N -LC film. The measurements were performed with excitation using unpolarized light at 367 nm. Reprinted with permission from [18]. Copyright 2012, American Chemical Society...

The N -LC film of D1 Doped (rac)-Poly-4 exhibited CPL similar to that of R)-l (S)-Poly-4 (Fig. 11.12b). The CPL spectra of DlDoped Poly-4 films showed handedness opposite to their counterparts in (lf)-/(S)-Poly-4, with gem values up to the order of 10 . The CPL spectrum of (roc)-Poly-4 showed no CPL therefore, the CPL of DlDoped (rac)-Poly-4 originated from the chiral induction of (rac)-Poly-4. The gem values of the chiral Poly-4 and doped Poly-4 N -LC films are listed in Table 11.3. 

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... 

Schlessinger, J., Warshel, A. Calculations of CD and CPL spectra as a tool for evaluatimi of the conformational differences between groimd and excited states of chiral molecules. Chem. Phys. Lett. 28, 380-383 (1974)... 

Figure 4 CPL spectra and total luminescence (lower curve) for an aqueous solution of Tb(DPA) containing 0.01 M o-glucose (upper curve) and L-glucose (middle curve).

Fig. 6.11 Absorption, total luminescence (TL), circular dichroism (CD), and circularly polarized luminescence (CPL) spectra of a chiral Os(ll) polypyridine complex in the spectral region comprised between 11,100 and 17,200 cm (CH3CN,...

The analysis of the CPL spectra constitutes a straightforward method for the study of the chirality of molecules in their luminescent excited states. By means of comparative CD/CPL measurements one can investigate the geometrical differences between the ground and excited states. The observation of CPL has the problems and limitations already described in the previous sections. In particular, the molecular or supramolecular species must contain a luminophore exhibiting a sufficiently high emission quantum yield. CPL spectroscopy, however, has a number of advantages in terms of specificity and selectivity that can be extremely useful in supramolecular chemistry, namely ... 

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