Spatial Separation of Dimers of Chiral Molecules

Eilam, A.; Shapiro, Moshe

doi:10.1103/physrevlett.110.213004

Cited by 33 publications

(30 citation statements)

References 15 publications

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“…It is well established that chiral molecules can exert discriminatory mechanical forces upon each other [13][14][15]. In recent years, interest has been expressed regarding the possibility of using light, such as that produced by a laser, to exert a mechanical force of discriminatory character upon a single chiral molecule [16][17][18][19][20][21]. The present paper is concerned with this possibility.…”

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confidence: 99%

Discriminatory optical force for chiral molecules

2014

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We suggest that the force F exerted upon a chiral molecule by light assumes the form F = a∇w + b∇h under appropriate circumstances, where a and b pertain to the molecule whilst w and h are the local densities of electric energy and helicity in the optical field; the gradients ∇ of these quantities thus governing the molecule's centre-of-mass motion. Whereas a is identical for the mirrorimage forms or enantiomers of the molecule, b has opposite signs; the associated contribution to F therefore pointing in opposite directions. A simple optical field is presented for which ∇w vanishes but ∇h does not, so that F is absolutely discriminatory. We then present two potential applications: a Stern-Gerlach-type deflector capable of spatially separating the enantiomers of a chiral molecule and a diffraction grating to which chiral molecules alone are sensitive; the resulting diffraction patterns thus encoding information about their chiral geometry.

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confidence: 99%

Discriminatory optical force for chiral molecules

2014

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“…The additional, distinctive optical force contribution that arises in cases of molecular chirality is expressible as F LjR r −∇U LjR r, leading to a differential force, ΔFr ≡ F L r − F R r, that quantifies a propensity for enantiomer separation-the means are to be discussed later. The broad context of optical methods for chiral discrimination is indeed a subject of considerable current interest [10][11][12][13][14][15][16][17]. An expression for such discrimination is determined from Eq.…”

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confidence: 99%

Laser optical separation of chiral molecules

Bradshaw

Andrews

2015

Opt. Lett.

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The optical trapping of molecules with an off-resonant laser beam involves a forward-Rayleigh scattering mechanism. It is shown that discriminatory effects arise on irradiating chiral molecules with circularly polarized light; the complete representation requires ensemble-weighted averaging to account for the influence of the trapping beam on the distribution of molecular orientations. Results of general application enable comparisons to be drawn between the results for two limits of the input laser intensity. It emerges that, in a racemic mixture, there is a differential driving force whose effect, at high laser intensities, is to produce differing local concentrations of the two enantiomers. Trapping of this type usually relates to the interaction of the laser field with a transition electric dipole, as shown by Fig. 1(a). Interactions between the irradiating beam and a transition magnetic dipole are also possible, but the associated coupling strength is usually much smaller in magnitude, and the effects are generally ignored. However, when considering the possibility of chiral discrimination (in which input light of left-handed circular polarization offers different observables compared to right-handed polarization), the conventional trapping mechanism involving only electric dipole transition moments has to be extended to accommodate transition magnetic dipoles [7]. In fact, the forward-Rayleigh scattering events most relevant in chiral discrimination involve a mixture of magnetic and electric dipole interactions, as illustrated by Fig. 1(b), with one kind of coupling involved in the input photon annihilation and the other in the output photon release.To understand the energetics in greater detail, we note that the underlying mechanism for the optical trapping of molecules is based on the variation of intensity within the optical beam, which produces a position-dependent lowering of energy for the molecules it encounters: the alternating electric field of the radiation may be interpreted as producing a dynamic Stark shift to the molecular ground state energy. In terms of quantum electrodynamics, the energy shift (which is quadratically dependent on the electric field of the light) has to originate in forward-Rayleigh scattering, i.e., the concerted annihilation and creation of photons with identical energy and wave-vector. In such a case, the optical wavelengths will lie in a region of transparency for the irradiated molecule-the throughput laser beam therefore emerges unchanged. The primary physical determinant of optical trapping is the potential energy U, whose evaluation from quantum theory requires that the initial and final states (here denoted by I) are identical [8]. An expression for U per molecule is determined from second-order time-dependent perturbation theory, i.e.,where S is an intermediate state of the system comprising both molecule and radiation, E is the energy of the state denoted by its subscript, and H int is the dipolar interaction Hamiltonian given byHere, μ and m are the electric and...

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“…The same logic applies if we change the handedness of the incident light, in a system comprising only one enantiomer; the radiation tensor changes in odd radiation-parity terms but not the others, and all of the molecular tensors remain unchanged (again, see figure 10). A variety of means by which the associated differences in local force might be used to engineer the separation of molecular enantiomers, and of chiral nanoparticles, have been proposed in recent years [43,[98][99][100][101][102][103][104][105][106][107][108][109][110], and the principles will be further discussed in section 11. Now let us observe how the matrix element feeds into an observable when the initial and final states differ-even if only in the state of the radiation field (as for example occurs in Rayleigh scattering or optical rotation).…”

Section: Transitions and Motionsmentioning

confidence: 99%

“…One of the main or implicit motivations for several of the recent studies in this area is the prospect of achieving, by optical means, a separation of particles-especially chiral molecules-of opposite handedness [7,10,43,[98][99][100][101][102][103][104][105][106][107][108][133][134][135][136][137][138][139][140][141][142][143][144][145]. Certainly such a capacity might have important commercial applications-notably in the pharmaceutical industry, where oppositely handed compounds can deliver drastically different effects.…”

Section: Relevance To Enantiomer Separationmentioning

confidence: 99%

Quantum formulation for nanoscale optical and material chirality: symmetry issues, space and time parity, and observables

Andrews

2018

J. Opt.

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To properly represent the interplay and coupling of optical and material chirality at the photonmolecule or photon-nanoparticle level invites a recognition of quantum facets in the fundamental aspects and mechanisms of light-matter interaction. It is therefore appropriate to cast theory in a general quantum form, one that is applicable to both linear and nonlinear optics as well as various forms of chiroptical interaction including chiral optomechanics. Such a framework, fully accounting for both radiation and matter in quantum terms, facilitates the scrutiny and identification of key issues concerning spatial and temporal parity, scale, dissipation and measurement. Furthermore it fully provides for describing the interactions of structured or twisted light beams with a vortex character, and it leads to the complete identification of symmetry conditions for materials to provide for chiral discrimination. Quantum considerations also lend a distinctive perspective to the very different senses in which other aspects of chirality are recognized in metamaterials. Duly attending to the symmetry principles governing allowed or disallowed forms of chiral discrimination supports an objective appraisal of the experimental possibilities and developing applications.

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Spatial Separation of Dimers of Chiral Molecules

Cited by 33 publications

References 15 publications

Discriminatory optical force for chiral molecules

Discriminatory optical force for chiral molecules

Laser optical separation of chiral molecules

Quantum formulation for nanoscale optical and material chirality: symmetry issues, space and time parity, and observables

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