Why Enantiopure Molecular Conductors

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  

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Two-terminal magnetochiral resistance anisotropy A/J(/,Bext) = lf(/,6ext) —f,Sext) of D (squares) and L (triangles) bismuth helices (seven turns, 8 mm diameter and 0.8 mm pitch) with I = 0.2 A, as a function of the external magnetic field Bext. at 300 K (top, Bq = 0.9 fl) and 77 K (bottom. Bo = 0.2 fl) (reproduced with permission from reference , copyright 2001, The American Physical Society). 

Rikken proposed that the EMCA effect could also result from the simultaneous application of a magnetic field and a current to a crystal with an enantiomorphous space group, and that it is a universal property. He showed the existence of this effect in the case of chiral single-walled carbon nanotubes.For most of the investigated tubes, a dependence of the resistance is observed that is odd in both the magnetic field and the current. These observations confirm the existence of EMCA not only for a macroscopic chiral conductor but also for a molecular conductor with chirality on the microscopic level. 

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