Anisotropy magnetochiral

There are other physical mechanisms proposed as sources of symmetry breaking, such as circularly polarized light, or magnetochiral anisotropy (Rikken and Raupach, 2000). 

In 1962 the first implicit prediction appeared of a cross-effect between natural and magnetic optical activity, which discriminates between the two enantiomers of chiral molecules [7]. This was followed independently by a prediction of magnetospatial dispersion in noncentrosymmetrical crystalline materials [8]. This cross-effect has been called magnetochiral anisotropy and has since been predicted independently several times more [9-12]. Its existence can be appreciated by expanding the dielectric tensor of a chiral medium subject to a magnetic field to first order in the wave vector k and magnetic field B [8] ... 

Here we define the magnetochiral anisotropy factor similarly ... 

Although there always seemed to be theoretical unanimity on the existence of magnetochiral anisotropy, it was not observed experimentally until a few years ago. The most strongly chiral optical transitions reported in the literature are the 5D0 —> 7 Fij2 luminescent transitions in tris(3-trifluoroacetyl- -camphorato) europium(III) complexes (Eu(( )tfc)3). These transitions also have a considerable MCD. Such complexes are therefore likely candidates to show a significant magnetochiral effect. The experiment performed by us to observe MChA measures the difference in luminescence intensity in the directions parallel and antiparallel to B [17,18]. In order to increase sensitivity, the magnetic field is alternated and the intensity difference 1B k is phase-sensitively detected by a... 

The first term on the right-hand side represents the pure magnetochiral anisotropy in absorption. The second term stems from a cascading of natural and magnetic circular dichroism. Cascading occurs because NCD creates an excess of one circularly polarized component in the initially unpolarized light. Because of this excess, the MCD then leads to an intensity modulation at ft. This cascaded MChA shows all the essential features of MChA given above but can be discriminated from the pure effect by its dependence on the sample thickness and on the concentration of the active species. 

In conclusion, we have described our observations of magnetochiral anisotropy in luminescence, absorption, asymmetric photochemistry, and electrical resistiv-... 

Raupach E. The Magnetochiral Anisotropy University of Konstanz. Hartung Gorre Verlag, Konstanz, 2002. 

Although there always seemed to be theoretical unanimity on the existence of magnetochiral anisotropy, it was not observed experimentally until a few years ago. The most strongly chiral optical transitions reported in the literature are the — Fi 2 luminescent transitions in tris(3-trifluoroacetyl- -camphorato)... 

Eor the definition of the asymmetry factors g, see Appendix A.) The first term is the Stevenson and Verdieck result [27] (for circularly polarized light, AH I = 1). The second term describes the enantiomeric excess due to the true magnetochiral anisotropy. 

There are two reasons for studying enantiomerically pure conductors. The first is connected with questions of structure. In effect, it is possible, starting from enantiopure bricks, to prepare crystal structures that are noncentrosymmetric, and which allow the disorder to be limited compared to the racemic derivatives. The second reason is linked to the fact that, for chiral conductors in an enantiopure form, theory predicts the existence of an effect called electrical magnetochiral anisotropy (EMCA) due to the simultaneous breaking of space and time symmetry in the presence of an external magnetic field. Thus, the resistivity of a chiral conductor depends on its absolute configuration according to the formula ... 

Throughout this chapter we have presented some examples of chiral enantiopure molecular materials. We have shown that chirality in molecular materials is not only a particular property governing the rotation sense of polarized light, but it also influences the solid state organization of materials and consequently their physical properties. Multifunctional enantiopure materials can also be at the forefront of such new phenomena as magnetochiral anisotropy or electric magnetochiral anisotropy. 

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