Browsing by Author "Kim, Gap-Sue"

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Dynamic Stark-Induced Coherent pi-Electron Rotations in a Chiral Aromatic Ring Molecule: Application to Phenylalanine
(2019-08-01)
Mineo, Hirobumi
;
Kim, Gap-Sue
;
Lin, Sheng Hsien
;
Fujimura, Yuichi
;
應用化學系分子科學碩博班
We present the results of a theoretical study on dynamic Stark-induced coherent pi-electron rotations in a chiral aromatic ring molecule. This is an extension of our previous papers, which have been published in Mineo, H. et al. [Phys. Chem. Chem. Phys. 2016, 18, 26786-26795] and Mineo, H. et al. [J. Phys. Chem. Lett. 2018, 9, 5521-5526]. In those papers, the time-dependent Schrodinger equation was solved under a restricted condition in which a degenerate excited state should be formed at the center of the two relevant excited states by dynamic Stark effects. The dynamic Stark-induced degenerate state (DSIDS) is essential to create unidirectional pi-electron rotations. In the present theoretical treatment, the above restriction is relaxed and the DSIDS is set to be at any energy position between the two excited states. This indicates a wide applicability of the dynamic Stark effects to coherent control of photophysical properties in aromatic molecules, such as coherent ring currents and current-induced magnetic fluxes of low-symmetric aromatic molecules. Analytical expressions for the coherent pi-electron angular momentum are derived within a three-electronic-state model by using the Laplace transform method. The validity of the developed theoretical procedure is demonstrated by carrying out simulations of the coherent angular momentum of L-phenylalanine. Effects of varying the DSIDS on the time-dependent coherent angular momentum and the populations in the three electronic states are examined, and the results are analyzed using approximate expressions for the time-dependent coherent angular momentum and the populations. Modulations in the time-dependent coherent angular momentum appear when the DSIDS is set at an energy position between the two excited states, while there are no beating modulations when the DSIDS is set at the center position. Such differences originate from whether interferences between the two dressed states take place or not.
Induction of unidirectional pi-electron rotations in low-symmetry aromatic ring molecules using two linearly polarized stationary lasers
(2016-10-14)
Mineo, Hirobumi
;
Yamaki, Masahiro
;
Kim, Gap-Sue
;
Teranishi, Yoshiaki
;
Lin, Sheng Hsien
A new laser-control scenario of unidirectional p-electron rotations in a low-symmetry aromatic ring molecule having no degenerate excited states is proposed. This scenario is based on dynamic Stark shifts of two relevant excited states using two linearly polarized stationary lasers. Each laser is set to selectively interact with one of the two electronic states, the lower and higher excited states are shifted up and down with the same rate, respectively, and the two excited states become degenerate at their midpoint. One of the four control parameters of the two lasers, i.e. two frequencies and two intensities, determines the values of all the other parameters. The direction of p-electron rotations, clockwise or counter-clockwise rotation, depends on the sign of the relative phase of the two lasers at the initial time. An analytical expression for the time-dependent expectation value of the rotational angular momentum operator is derived using the rotating wave approximation (RWA). The control scenario depends on the initial condition of the electronic states. The control scenario with the ground state as the initial condition was applied to toluene molecules. The derived time-dependent angular momentum consists of a train of unidirectional angular momentum pulses. The validity of the RWA was checked by numerically solving the time-dependent Schrodinger equation. The simulation results suggest an experimental realization of the induction of unidirectional p-electron rotations in low-symmetry aromatic ring molecules without using any intricate quantum-optimal control procedure. This may open up an effective generation method of ring currents and current-induced magnetic fields in biomolecules such as amino acids having aromatic ring molecules for searching their interactions.
On the validity of the independent interaction model for generation of dynamic Stark-induced degenerate states in chiral aromatic ring molecules
(2020-02-16)
Mineo, Hirobumi
;
Kim, Gap-Sue
;
Lin, Sheng Hsien
;
Fujimura, Yuichi
;
應用化學系
Dynamic Stark-induced degenerate state (DSIDS) is essential to generate electronic coherent angular momentum to identify molecular chirality. We previously derived DSIDS for phenylalanine enantiomers in the independent interaction model (IIM), in which two linearly polarized nonresonant UV lasers independently interact with relevant two electronic excited states. We present a numerical method to derive DSIDS beyond IIM. Here, both lasers interact with both excited states, and laser input parameters are determined for DSIDS located at the center of the excited states. The numerical results reasonably agree with those calculated in the IIM, which elucidate the validity of DSIDS in the IIM.
Quantum Design for Ultrafast Probing of Molecular Chirality through Enantiomer-Specific Coherent pi-Electron Angular Momentum
(2018-09-20)
Mineo, Hirobumi
;
Kim, Gap-Sue
;
Lin, Sheng Hsien
;
Fujimura, Yuichi
;
應用化學系
Probing molecular chirality, right-handed or left-handed chiral molecules, is one of the central issues in chemistry and biochemistry. The conventional theory of optical activity measurements such as circular dichroism has been derived in the second-order processes involving electric and magnetic dipole moments, and the signals are very weak. We propose an efficient enantiomer-probing scenario for chiral aromatic ring molecules based on photoinduced coherent pi-electron rotations. In our model, the resultant laser-induced currents themselves produce a strong magnetic field. The principle for probing molecular chirality is a utilization of dynamic Stark effects of two electronic excited states. These electronic states subjected to strong nonresonant linearly polarized UV lasers become degenerate to create enantiomer-specific electronic angular momentum. A pair of enantiomers of phenylalanine was taken as an example. Enantiomer-specific coherent magnetic fluxes on the order of a few teslas can be generated in several tens of femtoseconds. The direct detection of strong coherent magnetic fluxes could be carried out by time-resolved magnetic force microscopy experiments. The results provide important implications for the measurement of effective probing of chiral aromatic molecules.