Quantum Control of Isomerization and Enantiomer Preparation

Fujimura, Y.; González, Laura; Hoki, Kunihito; Manz, J.; Ohtsuki, Yukiyoshi; Umeda, Hiroaki

doi:10.1142/9789812791948_0003

Cited by 2 publications

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“…Most previous studies on quantum control of optical isomerization reactions have treated molecules possessing axial chirality mainly on the basis of a one-dimensional symmetric double-well potential model, as proposed by Hund just after the establishment of modern quantum mechanics . Selective preparation of pure enantiomers was modeled as an exchange between two enantiomers via a quantum tunneling through a one-dimensional double-well potential in the ground state or via an achiral electronic excited state. − An example of the former is H 2 POSH, which has axial chirality . The S−H torsion around the P−S bond was used as a one-dimensional reaction coordinate in that study.…”

Section: Introductionmentioning

confidence: 99%

Quantum Control of Molecular Chirality: Optical Isomerization of Difluorobenzo[c]phenanthrene

et al. 2002

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The results of a theoretical study are presented on quantum control of a chiral exchange reaction of a polyatomic molecule by using infrared laser pulses. Difluorobenzo[c]phenanthrene was chosen to be the simplest model for its helical chirality exchange reaction. This molecule has two stable configurations: M and P forms. From the viewpoint of chemical reaction dynamics, isomerization is regarded as the movement of one of the two representative points that initially correspond to the two forms to the position of the other representative point, while the other representative point remains in its initial position. The ground-state potential energy surface and dipole moment functions required to control this reaction were evaluated at the MP2/6-31+G(d,p) and MP2/TZV+(d,p) levels of molecular orbital (MO) theory. An effective potential energy surface (PES) that is a function of twisting motion of the benzene rings and wagging motion of the CF(2) group was constructed on the basis of the MO results. An analytical expression for the effective PES and that for the dipole moment functions were prepared to make the isomerization control tractable. A quantum control method in a classical way was applied to the isomerization of preoriented difluorobenzo[c]phenanthrene in low temperature limits. The time evolution of the representative point of the M form and that of the P form are separately evaluated to determine the optimal laser fields. This means that the laser control produces pure helical enantiomers from a racemic mixture. Representative points are replaced by the corresponding nuclear wave packets in this treatment. The derived control laser field consists of two linearly polarized E(x)() and E(z)() components that are perpendicular to each other. These components are pi-phase-shifted when the representative point is in the transition-state regions. Under the irradiation of this laser pulse, one of the two representative points of the isomerization is transferred to the target position along the intrinsic reaction path between the enantiomers, while the other representative point remains in its initial potential well. This results in one-way isomerization control, that is, the M(P) to P(M) form. The isomerization is completed with yields of ca. 70% within a few picoseconds. Temporal behaviors of the nuclear wave packet whose center corresponds to the representative point are drawn to see how the desired chiral exchange reaction proceeds in the presence of the control field, while its reverse process is suppressed.

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