Chiral molecules field effects

The electric field can also induce a tilt in the smectic A phase formed by chiral molecules (electroclinic effect). The tilt angle, 0, is linear with applied voltage i.e., no bistability is observed, in contrast to the smectic C phase. The electroclinic switching is remarkably faster than the ferroelectric one [6,7]. For numerous FLCPs, the electroclinic switching in the smectic A phase has been studied [51,54,62,123]. 

In the following sections we will first in Section 2 briefly discuss the necessary background to understand optical activity effects in linear and nonlinear optics and to illustrate the similarities and differences between both types. In Section 3 we present a more thorough analysis of nonlinear optical effects in second-harmonic generation, both from a theoretical and an experimental point of view. Section 4 deals with experimental examples that illustrate the usefulness of nonlinear optical activity in the study of chiral thin films and surfaces. Finally, in Section 5 we give an overview of the role of chirality in the field of second-order nonlinear optics and show that chiral molecules can be useful for applications in this field. 

Optical activity is the ability of a compound to rotate the plane of polarized light. This property arises from an interaction of the electromagnetic radiation of polarized light with the unsymmetric electric fields generated by the electrons in a chiral molecule. The rotation observed will clearly depend on the number of molecules exerting their effect, i.e. it depends upon the concentration. Observed rotations are thus converted into specific rotations that are a characteristic of the compound according to the formula below. 

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] ... 

IV. Field Effects in Chiral Molecules Computer Simulation.212... 

In Section IV the computer simulation is extended to describe the effects of excitation in chiral molecules and racemic mixtures of enantiomers. The modification of the dynamical properties brought about by mixing two enantiomers in equimolar proportion may be explained in terms of rotation-translation coupling. The application of an external field in this context ai iplifies the difference between the field-on acf s and cross-correlation of enantiomer and racemic mixture and provides a method of studying experimentally the fundamental phenomenon of rotation-translation coupling in the molecular liquid state of matter. 

In a chiral smectic (Sc ) phase, the tilt angle is the same within a layer, but the tilt direction processes and traces a helical path through a stack of layers (Figure 43). It has been demonstrated that when such a helix is completely unwound, as in a surface stabilized ferroelectric liquid crystal cell, then changing the tilt of the molecules fi om +0 to —0 by alternating the direction of an applied field results in a substantial electro-optic effect, which has the features of veiy fast switching (%1 - lOps), high contrast and bistability [87]. The smectic A phase of chiral molecules may also exhibit an electro-optic effect, this arises due to molecular tilt fluctuations which transition is approached, which are combined with a... 

A. Salam, On the Effect of a Radiation Field in Modifying the Intermolecular Interaction Between Two Chiral Molecules. J. Chem. Phys. 124 (2006) 014302. 

Recent employment of optically active fluorinated compounds for biologically active substances (7-2) or ferroelectric liquid crystals (3-5) has emphasized the versatility of these chiral molecules, while few methods have been reported for the preparation of such materials in a highly diastereo- as well as enantioselective manner. On the other hand, recent investigations in this field have opened the possibility for the introduction of chirality via asymmetric reduction or optical resolution by employing biocatalysts such as baker s yeast (6-75) or hydrolytic enzymes (16-20), respectively (27-23), along with the conventional chemical methodology (24-27). Chiral materials thus obtained may also be utilized in diastereoselective reactions which create new chiral centers (77). In this paper, the authors would like to discuss our recent progress in the preparation of optically active fluorinated compoounds and the effect of fluorine atom(s) on the reactivity and selectivity. 

The role of the skin as a portal of entry for chiral molecules is becoming an increasingly active and exciting field of research. To date, however, only a few investigations have been focused on the effect of enantiomeric differences of chiral drugs with respect to binding or metabolism in the skin on their transdermal delivery. There may be several sources for any observed enantioselectivity in terms of skin permeation of chiral drugs. For example, the components of the stratum corneum such as keratin and ceramides can serve as sources for chiral discrimination that could result in differential diffusion rates, dependent upon the stereochemistry of the solute. 

In the expression Eq. (5.33) we can see that the flexoelectric effect when it is combined with the piezoelectric effect (the second part of the coefficient /i) has similar effects as direct chiral interactions due to the van der Waals field having chiral s mimetry around the chiral molecules given by /i. We cannot distinguish between the two components as the piezoelectric coefficient Cp and the coefficient describing direct chiral interactions /i probably depend equally (they are proportional) on the enantiomeric excess. 

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