Dynamic-coupling mechanisms

In this way, a As value of —0.57 is calculated at 250 nm, as compared with an experimental value of —0.63. This excellent agreement between the experimental and calculated values is a strong indication that a dynamic coupling mechanism is the major source of optical activity in these molecules. 

The dynamic coupling mechanism predicts that hypersensitivity should be observed when the point group of the lanthanide complex contains Y3m spherical harmonics in the expansion of the point potential. The good agreement between the calculated and observed values for Tj or Q.2 parameters shows that the dynamic coupling mechanism makes a significant contribution to the intensities of the quadrupole allowed f-electron transitions in lanthanide complexes. Qualitatively, the mechanism is allowed for all lanthanide group symmetries in which the electric quadrupole component 6,a,fi and the electric dipole moment p, a transform under a common representation. 

Studies involving temperature dependence of the oscillator strengths of the hypersensitive transitions and circular dichroism (CD) and magnetic circular dichroism (MCD) of optically active complexes may give some useful information from which the relative contributions of static and dynamic coupling mechanisms to the observed oscillator strengths may be ascertained. 

Crystal field theory, intensities of 4f-4f transitions, Judd-Ofelt theory of electric-dipole transitions, covalency model of hypersensitivity, dynamic coupling mechanism, solution spectra, spectral data for complexes, solvent effects, fluorescence and photochemistry of lanthanide complexes are dealt with in spectroscopy of lanthanide complexes. 

The dynamic coupling mechanism (Fig. 7c) only makes a contribution to the intensity of an EQ transition for a system with point group symmetry... 

However, neither the inhomogeneous dielectric mechanism nor its equivalent, the dynamic-coupling mechanism, makes allowance for the polarizability of the outer shells of the rare-earth or actinide ion. For an external quadrupole field to penetrate to the f electrons, we must include a screening factor (1- o ) the same factor must be introduced if we take the point of view of dynamic coupling and ask what reduction the quadrupole field of the f electrons experiences as it penetrates out to the ligands. For a... 

The experimental results indicate that the substitution of water molecules by a phen molecule into the coordination sphere of a Eu-eta complex enhances the luminescence intensity due to the lowering of the number of OH oscillators (which suppress the luminescence), as well as the ability of phen to act as a good chromo-phor. Furthermore, the in situ organofunctionalized silica-eta complex exhibits an optimization of optical properties, in comparison with the free complex, mainly an enhancement of the emission intensity. The experimental parameters show that the dynamic coupling mechanism is predominant. 

Reid and Richardson (1983b, 1985a) used this property to disentangle the two mechanisms, and Reid et al. (1983) showed that in many cases the dynamic-coupling mechanism plays the dominant role. However, Poon and Newman (1984) have pointed out that the absence of any consideration of overlap and covalency in that kind of work still leaves something to be desired. 

While over the years several explanations have been proposed for hypersensitivity, including symmetry arguments, vibronic, charge-transfer and electric-quadrupole transition contributions [57,58], the most successful to date has been the dynamic coupling mechanism proposed by Mason et al. [60]. These authors suggest that the intensity of the hypersensitive transitions results from a non-zero electric dipole transition, which arises from an electric dipole in the ligand induced by the/orbitals of the metal ion. By analogy... 

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