Browsing by Author "Fujimura, Yuichi"

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Ab initio quantum dynamical analysis of ultrafast nonradiative transitions via conical intersections in pyrazine
(2015-01-01)
Kanno, Manabu
;
Ito, Yuta
;
Shimakura, Noriyuki
;
Koseki, Shiro
;
Kono, Hirohiko
We theoretically investigated the mechanism of ultrafast nonradiative transition through conical intersections in photoexcited pyrazine by ab initio quantum dynamical calculations. This work was motivated by the recent theoretical and experimental studies that presented conflicting results: the former is the on-the-fly semiclassical surface hopping calculation combined with the time-dependent density functional theory, which showed that nonadiabatic transitions from the optically bright S-2 (B-1(2u), pi pi*) state to the optically dark S-3 ((1)A(u), n pi*) and S-4 (B-1(2g), n pi*) states take place predominantly at the initial stage of electronic relaxation [U. Werner et al., Chem. Phys., 2008, 349, 319]; the latter is the pump-probe photoelectron spectroscopic measurement, which reported the S2 lifetime (22 +/- 3 fs) of nonradiative decay to the almost dark S-1 (B-1(3u), n pi*) state [Y.-I. Suzuki et al., J. Chem. Phys., 2010, 132, 174302]. We constructed adiabatic and diabatic potential energy surfaces of these pi pi* and n pi* states using the multireference configuration interaction method and calculated their diabatic couplings within two-dimensional subspaces spanned by selected ground-state normal coordinates. Contrary to the surface hopping study, our nuclear wave packet simulations demonstrated that nonadiabatic transitions to the S-3 and S-4 states are so small that the conventional two-state (S-1 and S-2) picture is valid. Ultrafast internal conversion of pyrazine, which is deemed to proceed with a 22 fs lifetime, in fact consists of three consecutive steps: (i) the wave packet excited to the S-2 state travels toward the S-2-S-1 conical intersection in 10 fs, (ii) the nonadiabatic transition to the S-1 state progresses at a rapid rate corresponding to a transient lifetime of 7 fs, and (iii) intramolecular vibrational energy redistribution occurs in the S-1 state in about 80 fs after optical excitation. To verify this prediction, time-resolved experiments with a resolution of several fs or shorter are desirable.
Ab Initio Quantum Dynamical Study on Ultrafast Nonradiative Transition Pathways of Pyrazine
(2015-01-01)
Kanno, Manabu
;
Ito, Yuta
;
Shimakura, Noriyuki
;
Koseki, Shiro
;
Kono, Hirohiko
We theoretically verified the participation of optically dark n pi* states other than S-1 in ultrafast internal conversion of pyrazine. Contrary to a recent semiclassical study, our quantum dynamical calculations demonstrated that their contributions are negligible.
Coherent ring currents in chiral aromatic molecules induced by linearly polarized UV laser pulses
(2013)
Kanno, Manabu
;
Kono, Hirohiko
;
Mineo, Hirobumi
;
Lin, Sheng Hsien
;
Fujimura, Yuichi
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.
Laser manipulation of localised pi-electron rotations in a molecule with two aromatic rings
(2017-01-01)
Yamaki, Masahiro
;
Teranishi, Yoshiaki
;
Lin, Sheng Hsien
;
Fujimura, Yuichi
;
應用化學系
Coherent dynamics of localised pi-electron rotations in an aromatic ring molecule may play an important role in designing next generation photo-induced organic molecular devices. In this paper, we present a theoretical study of laser control of localised pi-electron rotations in a low symmetry aromatic ring molecule, which are created by the coherence of two or more electronic excited states. The control scenario is to manipulate energy spacings between two electronic states by utilising AC Stark shift induced by strong non-resonant ultraviolet (UV) laser. We set three targets for laser manipulation of localised electron rotational dynamics for (P)-2,2'-biphenol with two aromatic rings. The first target is flipping of the direction of the localised pi-electron rotation on the same ring, the second one is the transfer of the pi-electron rotation localisation from one aromatic ring to the other, and the third one is freezing the unidirectional pi-electron rotation localised on one aromatic ring. We propose the fundamental principle of laser manipulation of localised pi-electron rotation utilising AC Stark shift. Expectation values of the localised electron angular momentum are calculated numerically to demonstrate our idea of laser manipulation. Effects of laser-field intensity on localised electron rotation dynamics are briefly discussed.
Laser-Control of Ultrafast pi-Electron Ring Currents in Aromatic Molecules: Roles of Molecular Symmetry and Light Polarization
(2018-12-01)
Kanno, Manabu
;
Kono, Hirohiko
;
Fujimura, Yuichi
;
應用化學系分子科學碩博班
;
Institute of Molecular science
Being motivated by the recent progress in attosecond laser technology, we theoretically explore the strategy of inducing ultrafast electron dynamics inherent to aromatic molecules, i.e., ring currents by means of polarized laser pulses. The main topic of discussion is how to control the direction of ring currents in an aromatic molecule of low symmetry, for which the design of an efficient control pulse cannot be achieved intuitively. We first consider a system with a single aromatic ring and show that coherent pi-electron angular momentum, which oscillates with time, can be produced and controlled by a polarized laser pulse with its ellipticity and orientation properly chosen. Nonadiabatic couplings with molecular vibration gradually weaken the angular momentum, while the vibrational amplitude strongly depends on the polarization of incident light. This suggests the conversion of the polarization dependence of ring current into that of subsequent vibration, which may open a way to detect laser-driven ultrafast electron dynamics by vibrational spectroscopy. The laser-control scheme for the ring current is then extended to a molecule with two aromatic rings, which exhibits characteristic phenomena absent in that with a single ring. We demonstrate that two-dimensional switching of the direction of angular momentum is possible in such molecules. In addition, ring current can be localized at a specific ring by tailored lasers. The application of the present control method to polycyclic aromatic hydrocarbons will lead to the development of next-generation organic optical switching devices.
Laser-Polarization Effects on Coherent Vibronic Excitation of Molecules with Quasi-Degenerate Electronic States
(2012-11-22)
Kanno, Manabu
;
Ono, Yukari
;
Kono, Hirohiko
;
Fujimura, Yuichi
;
應用化學系分子科學碩博班
The laser-polarization effects on nonadiabatically couple pi-electron rotation (ring current) and molecular vibration have been theoretically analyzed for aromatic molecules with quasi-degenerate excited states irradiated by an ultrashort laser pulse of arbitrary polarization. We first derived general formulations of the coherent electronic wave packet and expectation value of electronic angular momentum within a frozen-nuclei model. The relative quantum phase of the superposed quasi-degenerate States, which.. determines the oscillating behavior of angular momentum; can be manipulated by the ellipticity and orientation of the incident laser. Nuclear wave packet simulations with a model molecule confirmed the controllability of pi-electron rotation, although the angular momentum is gradually reduced by nonadiabatic couplings. The amplitude of molecular vibration depends prominently on the orientation of linear polarization vectors rather than the helicity of circular polarization. The characteristic feature in vibrational amplitudes is attributed to the interference in nonadiabatic transition governed by the-relative quantum phase between nuclear wave packets. This offers a new strategy for laser control of molecular vibrations through the wave packet interference in nonadiabatic transition.
Neutral-Fragmentation Paths of Methane Induced by Intense Ultrashort IR Laser Pulses: Ab Initio Molecular Orbital Approach
(2013-01-17)
Koseki, Shiro
;
Shimakura, Noriyuki
;
Teranishi, Yoshiaki
;
Lin, Sheng Hsien
;
Fujimura, Yuichi
Instantaneous (laser-field-dependent) potential energy curves leading to neutral fragmentations of methane were calculated at several laser intensities from 1.4 x 10(13) to 1.2 x 10(14) W/cm(2) (from 1.0 x 10(10) to 3.0 X 10(10) V/m) using ab initio molecular orbital (MO) methods to validate the observation of neutral fragmentations induced by intense femtosecond IR pulses (Kong et al. J. Chem. Phys. 2006, 125, 133320). Two fragmentation paths, CH2 + 2H and CH2 + H-2, in T-1(2) superexcited states that are located in the energy range of 12-16 eV were considered as the reaction paths because these states are responsible for Jahn-Teller distortion opening up reaction paths during ultrashort pulses. As field intensity increased, the low-lying excited (1)A(1) states originated from the Jahn-Teller T-1(2) states were substantially stabilized along the neutral-fragment path CH4 -> CH2 + 2H and were located below the ionization threshold. On the other hand, the low-lying excited B-1(1) states, which also originate from the Jahn-Teller T-1(2) states, were embedded on the ionized state along the dissociation path to CH2 + H-2. This indicates that ionic fragments, rather than neutral ones, are produced along the CH2 + H-2 path. The computational results support neutral fragmentations through superexcited states proposed by Kong et al.
Nonadiabatic Response Model of Laser-Induced Ultrafast pi-Electron Rotations in Chiral Aromatic Molecules
(2010-03-12)
Kanno, Manabu
;
Kono, Hirohiko
;
Fujimura, Yuichi
;
Lin, Sheng H.
;
應用化學系
We theoretically investigated the nonadiabatic couplings between optically induced pi-electron rotations and molecular vibrations in a chiral aromatic molecule irradiated by a nonhelical, linearly polarized laser pulse. The results of wave packet dynamics simulation show that the vibrational amplitudes strongly depend on the initial rotation direction, clockwise or counterclockwise, which is controlled by the polarization direction of the incident pulse. This suggests that attosecond pi-electron rotations can be observed by spectroscopic detection of femtosecond molecular vibrations.
Nonadiabatically Coupled pi-Electron Rotation and Molecular Vibration in Aromatic Molecules Excited by Polarized UV/Vis Laser Pulses
(2014-02-01)
Kanno, Manabu
;
Ono, Yukari
;
Kono, Hirohiko
;
Fujimura, Yuichi
;
應用化學系分子科學碩博班
We review our theoretical studies on laser-driven ultrafast pi-electron rotation (ring current) and vibronically coupled molecular vibrations in aromatic molecules with quasi-degenerate excited states. The main focus of discussion is on the role of laser polarization in controlling the coherent vibronic dynamics. We first present general formulations of the coherent electronic wave packet and expectation value of electronic angular momentum for arbitrary laser polarization within a frozen-nuclei model. We show that the relative quantum phase of the superposed quasi-degenerate states, which determines the oscillating behavior of angular momentum, can be manipulated by the ellipticity and orientation of the incident laser. The controllability of pi-electron rotation is demonstrated by electronic wave packet simulations for a model molecule. The results of nuclear wave packet simulations on effective potential energy surfaces of the molecule have revealed that the angular momentum is gradually reduced by nonadiabatic transitions. The amplitude of induced molecular vibration depends significantly on the direction of linear polarization vectors but is insensitive to the helicity of circular polarization. The characteristic feature in vibrational amplitudes is attributed to the interference between nuclear wave packets that acquire different quantum phases in nonadiabatic transition. This feature offers a new strategy for laser control of molecular vibrations through the wave packet interference in nonadiabatic transition.
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 Chemical Calculations of Intramolecular Vibrational Redistribution and Energy Transfer of Dipeptides (GlyTyr and LeuTyr) and Applications to the RRKM Theory
(2013-07-01)
Yang, Ling
;
Niu, Yingli
;
Zhu, Chaoyuan
;
Fujimura, Yuichi
;
Shiu, Yingjen
Recently the quantum chemistry program can provide the anharmonic potentials for polyatomic molecules and clusters. It makes the quantum calculation of intramlecular vibrational redistribution (IVR) rates and intramolecular vibrational energy transfer possible. In the present paper, we apply the adiabatic approximation method to treat these two intramolecular energy redistribution processes. Using this method, we calculate the IVR rates of the dipeptides (glycyl tyrosine (GlyTyr) and leucyl tyrosine (LeuTyr)) and their cation radicals from the high frequency modes to the low frequency modes. Our theoretical results of the IVR lifetimes of the high frequency modes, like C-H, N-H, and O-H stretching modes, for both GlyTyr and LeuTyr molecules and their cation radicals are about 1 ps, 10 ps, and 100 ps, respectively. It provides theoretical support for the claim that IVR takes place prior to dissociation and the IVR rates are determined by the functional group rather than the degrees of freedom of the system. Thus the Rice-Ramsperger-Kassel-Marcus (RRKM) theory is suitable for investigating the photodissociation process of dipeptides. In addition, the calculated intramolecular energy transfer rate from O-H stretching mode of the C-termius of dipeptides to N-H mode of N-terminus is close to IVR rate.
Quantum coherent pi-electron rotations in a non-planar chiral molecule induced by using a linearly polarized UV laser pulse
(2015-01-01)
Mineo, Hirobumi
;
Fujimura, Yuichi
;
應用化學系分子科學碩博班
;
Institute of Molecular science
We propose an ultrafast quantum switching method of pi-electron rotations, which are switched among four rotational patterns in a nonplanar chiral aromatic molecule (P)-2,2'-biphenol and perform the sequential switching among four rotational patterns which are performed by the overlapped pump-dump laser pulses. Coherent pi-electron dynamics are generated by applying the linearly polarized UV pulse laser to create a pair of coherent quasi-degenerated excited states. We also plot the time-dependent pi-electron ring current, and discussed ring current transfer between two aromatic rings.
Quantum Control of Coherent -Electron Dynamics in Chiral Aromatic Molecules
(2016-01)
Yamaki, Masahiro
;
Mineo, Hirobumi
;
Teranishi, Yoshiaki
;
Lin, Sheng Hsien
;
Fujimura, Yuichi
Control of mobile -electrons is one of the fundamental issues in the organic optoelectronics for designing the next generation ultrafast switching devices. The optimal control simulations of coherent -electron rotations in (P)-2,2\'-biphenol, which is the typical nonplanar aromatic molecule with axial chirality, were performed by taking into account two types of the control targets: one is generation of the maximum -angular momentum, and the other is the maintaining of the generated unidirectional angular momentum during a setting time duration. The optimal control pulse for each target is designed. The analysis of the simulation results shows that the effective maintaining of the unidirectional angular momentum can be realized by applying 2 pulse to one of the electronic excited states forming the coherent electronic state. The 2 pulse prevents the reverse rotation of the -electrons by dumping the excited state population to the ground state and subsequently by pumping the population back to the excited state. The present results provide a theoretical basis for the designing next generation ultrafast switching devices made by organic aromatic molecules.
Quantum Control of Coherent -Electron Dynamics in Chiral Aromatic Molecules
(2016-01-01)
Yamaki, Masahiro
;
Mineo, Hirobumi
;
Teranishi, Yoshiaki
;
Lin, Sheng Hsien
;
Fujimura, Yuichi
Control of mobile -electrons is one of the fundamental issues in the organic optoelectronics for designing the next generation ultrafast switching devices. The optimal control simulations of coherent -electron rotations in (P)-2,2\'-biphenol, which is the typical nonplanar aromatic molecule with axial chirality, were performed by taking into account two types of the control targets: one is generation of the maximum -angular momentum, and the other is the maintaining of the generated unidirectional angular momentum during a setting time duration. The optimal control pulse for each target is designed. The analysis of the simulation results shows that the effective maintaining of the unidirectional angular momentum can be realized by applying 2 pulse to one of the electronic excited states forming the coherent electronic state. The 2 pulse prevents the reverse rotation of the -electrons by dumping the excited state population to the ground state and subsequently by pumping the population back to the excited state. The present results provide a theoretical basis for the designing next generation ultrafast switching devices made by organic aromatic molecules.
Quantum control of coherent pi-electron ring currents in polycyclic aromatic hydrocarbons
(2017-12-14)
Mineo, Hirobumi
;
Fujimura, Yuichi
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
We present results for quantum optimal control (QOC) of the coherent pi electron ring currents in polycyclic aromatic hydrocarbons (PAHs). Since PAHs consist of a number of condensed benzene rings, in principle, there exist various coherent ring patterns. These include the ring current localized to a designated benzene ring, the perimeter ring current that flows along the edge of the PAH, and the middle ring current of PAHs having an odd number of benzene rings such as anthracene. In the present QOC treatment, the best target wavefunction for generation of the ring current through a designated path is determined by a Lagrange multiplier method. The target function is integrated into the ordinary QOC theory. To demonstrate the applicability of the QOC procedure, we took naphthalene and anthracene as the simplest examples of linear PAHs. The mechanisms of ring current generation were clarified by analyzing the temporal evolutions of the electronic excited states after coherent excitation by UV pulses or (UV+IR) pulses as well as those of electric fields of the optimal laser pulses. Time-dependent simulations of the perimeter ring current and middle ring current of anthracene, which are induced by analytical electric fields of UV pulsed lasers, were performed to reproduce the QOC results. Published by AIP Publishing.
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.
Quantum Design of pi-Electron Ring Currents in Polycyclic Aromatic Hydrocarbons: Parallel and Antiparallel Ring Currents in Naphthalene
(2017-05-04)
Mineo, Hirobumi
;
Fujimura, Yuichi
;
應用化學系分子科學碩博班
;
Institute of Molecular science
Control of pi-electrons in polycyclic aromatic hydrocarbons (PAHs) is one of the fundamental issues in optoelectronics for ultrafast optical switching devices. We have proposed an effective scenario for design of the generation of coherent ring currents in naphthalene (D-2h), which is the smallest, unit of planar PAHs. It has been demonstrated by using quantum chemical calculations and quantum optimal control (QOC) simulations that two types of ring currents, parallel and antiparallel, can be generated by resonance excitations by two linearly polarized lasers. A parallel (antiparallel) ring current means that the currents of two benzene rings run in the same (opposite) directions. The two types of ring currents may be experimentally identified by magnetic force microscopy. The QOC simulations indicate that a parallel ring current can be generated by using continuous wave and Gaussian pulse lasers with their time delay without relying on a sophisticated experimental apparatus. The present results provide a guiding principle of coherent it-electronics in PAHs for next-generation organic optical switching devices.
Quantum Localization of Coherent pi-Electron Angular Momentum in (P)-2,2 '-Biphenol
(2014-06-05)
Yamaki, Masahiro
;
Mineo, Hirobumi
;
Teranishi, Yoshiaki
;
Hayashi, Michitoshi
;
Fujimura, Yuichi
Controlling g-electrons with delocalized character is one of the fundamental issues in femtosecond and attosecond chemistry. Localization of pi-electron rotation by using laser pulses is expected to play an essential role in nanoscience. The pi-electron rotation created at a selected aromatic ring of a single molecule induces a local intense electromagnetic field, which is a new type of ultrafast optical control functioning. We propose a quantum localization of coherent pi-electron angular momentum in (P)-2,2'-biphenol, which is a simple, covalently linked chiral aromatic ring chain molecule. The localization considered here consists of sequential two steps: the first step is to localize the pi-electron angular momentum at a selected ring of the two benzene rings, and the other is to maintain the localization. Optimal control theory was used for obtaining the optimized electric fields of linearly polarized laser pulses to realize the localization. The optimal electric fields and the resultant coherent electronic dynamics are analyzed.