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

Abstract

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.

Circular Dichroism in Ion Yields of Femtosecond‐Laser Mass Spectrometry

“…The quest for stereo-selective synthesis has stimulated considerable interest in attempts to either separate or transform enantiomers by means of laser excitation employing different kinds of circular polarization. [6,7] Furthermore, CD effects are not limited to the linear regime, as measurements of two-and multiphoton CD effects have been the topic of experimental [8] and theoretical [9,10] reports as well. Recently, CD measurements have been combined with laser mass spectrometry utilizing multi-photon ionization.…”

Size Dependence of Nanoscale Confinement on Chiral Transformation

“…[50] The stable geometries of P and M chiral enantiomers of D molecules were situated in one of the symmetric double potential wells. [16] The chiral character of different enantiomers can be characterized by dihedral angle of four atoms (a-b-c-d) shown in Figure 1 (top). When the dihedral angle is averaged over a certain time period (here, we use 0.1 ns), the value of the chiral character is positive if the form belongs to a P enantiomer and negative if it is an M enantiomer.…”

“…We used the (13,4), (14,5), (15,6), (16,7), and (17,8) SWBNNTs with diameters ranging from 12.0 to 17.3 . The lengths of these SWBNNTs are about 40 .…”

“…The D molecule has been observed to show the helical chirality transition by using infrared laser pulses. [16] The energy barrier for the chirality transition in bulk was estimated to be only 6.7-8.0 kcal mol À1 , [16] which indicates that it might be possible to observe this chiral transition in classical MD simulations, particularly with the help of SWBNNT confinements (as shown below the barrier is reduced significantly inside the SWBNNTs). This type of helical chirality transition has also been observed with MD simulations recently for another molecule, 1,2-(1,1-binaphthalene-2,2'-diyldisulfonyl)ethylene, inside a twisted chiral carbon nanotube.…”

Small Molecules and Peptides Inside Carbon Nanotubes: Impact of Nanoscale Confinement

“…Molecular systems can be chiral by asymmetrically arranging atoms in space around a center, axis, or plane, which are called point, axial, and planar chirality, respectively [69]. It has been reported using infrared laser pulses that D molecule show the planar chirality transition between P-enantiomer and Menantiomer, and the energy barrier for this transition in bulk was estimated to be only 6.7-8.0 kcal/mol [70]. The chiral character of enantiomers can be characterized by dihedral angle of four atoms (a-b-c-d) shown in Fig.…”