Strong coupling scheme

Energy migration in concentrated systems has been an issue of research in the last decade. Especially since lasers became easily available, the progress has been great. In Section VIII we will first consider the case that S is an ion to which the weak-coupling scheme applies. In practice this case consists of the trivalent rare earth ions. Subsequently we will deal with the case where S is an ion to which the intermediate-or strong-coupling scheme applies. 

An appropriate way to close this section is to consider the radiationless transition that may occur by electron transfer, because it certainly belongs to the strong-coupling scheme. A rare-earth ion may lose its excitation energy not only by energy transfer, but also by electron transfer to other centers (121). The problem can be nicely illustrated by a molecular species, viz., the decatungstates [RE WioOae] " (122). 

It is usual to call the AR = 0 situation the weak-coupling scheme, AR > 0 the intermediate-coupling scheme, and AR > 0 the strong-coupling scheme. The word coupling relates to the coupling between the electrons and the vibrations of the center considered. The value of AR measures the strength of this interaction. 

The Stokes shift of the Cu" emission is usually large (> 5000 cm ), indicating the strong-coupling scheme. About the Ag ion less is known, but what is known shows a similarity with the Cu" " data. 

LML angles are allowed to change as the rotation proceeds. The net result is that alkene rotation and Berry pseudorotation are strongly coupled (Scheme 4)... 

Palladium-mediated catalysis has only been exploited relatively recently in the synthesis of substituted PPV derivatives. The use of aryl dibromides as monomers is particularly useful as it allows the synthesis of PPVs substituted with alkyl rather than alkoxy sidechains. The Suzuki [53, 54], Heck [55], and Stille [56] reactions have been used in the synthesis of new PPV derivatives, but attaining high molecular weight PPV derivatives by these methodologies has proved problematic. A phenyl-subslilutcd PPV material PPPV 31 was synthesized by a Suzuki coupling (Scheme 1-10) of dibromoethene and fo/.v-boronic acid 30. Its absorption (2ni ix=385 nm) and emission (2max=475 nm) maxima were strongly... 

A recent publication by the group of Barbarella has disclosed the rapid preparation of poorly soluble unsubstituted and modified a-quinque- and sexithiophenes by the extensive use of bromination/iodination steps and microwave-assisted Suzuki and Sonogashira cross-couplings (Scheme 6.16) [42]. Suzuki reactions were either carried out under solvent-free conditions on a strongly basic potassium fluoride/ alumina support for the synthesis of soluble oligothiophenes, or in solution phase for the preparation of the rather insoluble a-quinque- and sexithiophenes. In both cases, 5 mol% of [l,l -bis(diphenylphosphino)ferrocene]dichloropalladium(II)... 

Due to the localization of the 5 f electrons in the oxides a final state multiplet structure is expected. Therefore, these spectra have been compared with final state intensities calculated in an intermediate coupling scheme which accoimts for the strong spin-orbit... 

---