Browsing by Author "Yamaki, Masahiro"

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A theoretical study on the spectroscopy and the radiative and non-radiative relaxation rate constants of the S(0) (1)A(1)-S(1) (1)A(2) vibronic transitions of formaldehyde
(2010-01-01)
Lin, Chih-Kai
;
Li, Ming-Chung
;
Yamaki, Masahiro
;
Hayashi, Michitoshi
;
Lin, Sheng Hsien
We have carried out a close examination on the mathematical treatments and the first-principle computations concerning the vibronic transitions between the S(0) (1)A(1) and the S(1) (1)A(2) states of formaldehyde. The simulation of absorption spectrum was presented with peak intensities calculated according to vibronic-coupled transition dipole moments and Franck-Condon factors. The radiative and non-radiative transition rate constants from the excited to the ground states were calculated with formulas based on Fermi's golden rule. It is concluded that our simulated absorption spectrum between 300 and 360 nm, as well as the estimated relaxation rate constants, showed good agreements with experimental reports.
A theoretical study on the spectroscopy and the radiative and non-radiative relaxation rate constants of the S-0 (1)A(1)-S-1 (1)A(2) vibronic transitions of formaldehyde
(2010-01-01)
Lin, Chih-Kai
;
Li, Ming-Chung
;
Yamaki, Masahiro
;
Hayashi, Michitoshi
;
Lin, Sheng Hsien
We have carried out a close examination on the mathematical treatments and the first-principle computations concerning the vibronic transitions between the S-0 (1)A(1) and the S-1 (1)A(2) states of formaldehyde. The simulation of absorption spectrum was presented with peak intensities calculated according to vibronic-coupled transition dipole moments and Franck-Condon factors. The radiative and non-radiative transition rate constants from the excited to the ground states were calculated with formulas based on Fermi's golden rule. It is concluded that our simulated absorption spectrum between 300 and 360 nm, as well as the estimated relaxation rate constants, showed good agreements with experimental reports.
Franck-Condon simulation of the A (1)B(2) -> X (1)A(1) dispersed fluorescence spectrum of fluorobenzene and its rate of the internal conversion
(2011-03-07)
He, Rongxing
;
Yang, Ling
;
Zhu, Chaoyuan
;
Yamaki, Masahiro
;
Lee, Yuan-Pern
By using three different hybrid exchange-correlation functionals containing 20%, 35%, and 50% of exact Hartree-Fock (HF) exchange of the density functional theory and its time-dependent extension plus the Hartree-Fock and the configuration interaction of single excitation methods, equilibrium geometries, and their 30 vibrational-normal-mode frequencies of the ground S(0)((1)A(1)) and the first excited S(1)((1)B(2)) states of fluorobenzene (FB) were calculated. The dispersed fluorescence spectrum and internal conversion (IC) rate of the A (1)B(2) -> X (1)A(1) transition were simulated by Franck-Condon (FC) calculations within the displaced harmonic oscillator approximation plus anharmonic and distorted corrections. The simulated spectral profile is primarily described by the Franck-Condon progression from the ring-breathing modes v(9) and v(10) which belong to totally symmetry modes. Anharmonic corrections simultaneously improve the intensity order of 9(1)(0) and 10(1)(0) bands and diminish 1(1)(0) transition that is fairly strong in harmonic simulations. It is concluded that the amount of Hartree-Fock exchange does impact the geometries and vibrational frequencies of FB molecule, but not the relative intensities of the transitions. It is anharmonic corrections that make the relative intensities of the transitions in good agreement with experimental results. Distorted corrections could assign most of the dominant overtones of out-of-plane nontotally symmetry modes, and the results agree well with the experimental assignments. Furthermore, it was found that the internal conversion rate is dominated by three promoting modes that are computed with lowing symmetry to C(1). By choosing dephasing width as 10 cm(-1) that is consistent with spectral simulation, we obtained the lifetimes of the A (1)B(2) -> X (1)A(1) de-excitation as 11 and 19 ns, respectively, from TD(B3LYP) and HF/CIS calculations in comparison with the experimental value 14.75 ns. (c) 2011 American Institute of Physics. [doi:10.1063/1.3559454]
Franck-Condon simulation of the A B-1(2) -> X (1)A(1) dispersed fluorescence spectrum of fluorobenzene and its rate of the internal conversion
(2011-03-07)
He, Rongxing
;
Yang, Ling
;
Zhu, Chaoyuan
;
Yamaki, Masahiro
;
Lee, Yuan-Pern
By using three different hybrid exchange-correlation functionals containing 20%, 35%, and 50% of exact Hartree-Fock (HF) exchange of the density functional theory and its time-dependent extension plus the Hartree-Fock and the configuration interaction of single excitation methods, equilibrium geometries, and their 30 vibrational-normal-mode frequencies of the ground S-0((1)A(1)) and the first excited S-1(B-1(2)) states of fluorobenzene (FB) were calculated. The dispersed fluorescence spectrum and internal conversion (IC) rate of the A B-1(2) -> X (1)A(1) transition were simulated by Franck-Condon (FC) calculations within the displaced harmonic oscillator approximation plus anharmonic and distorted corrections. The simulated spectral profile is primarily described by the Franck-Condon progression from the ring-breathing modes v(9) and v(10) which belong to totally symmetry modes. Anharmonic corrections simultaneously improve the intensity order of 9(1)(0) and 10(1)(0) bands and diminish 1(1)(0) transition that is fairly strong in harmonic simulations. It is concluded that the amount of Hartree-Fock exchange does impact the geometries and vibrational frequencies of FB molecule, but not the relative intensities of the transitions. It is anharmonic corrections that make the relative intensities of the transitions in good agreement with experimental results. Distorted corrections could assign most of the dominant overtones of out-of-plane nontotally symmetry modes, and the results agree well with the experimental assignments. Furthermore, it was found that the internal conversion rate is dominated by three promoting modes that are computed with lowing symmetry to C-1. By choosing dephasing width as 10 cm(-1) that is consistent with spectral simulation, we obtained the lifetimes of the A B-1(2) -> X (1)A(1) de-excitation as 11 and 19 ns, respectively, from TD(B3LYP) and HF/CIS calculations in comparison with the experimental value 14.75 ns. (c) 2011 American Institute of Physics. [doi:10.1063/1.3559454]
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.
Molecular Dynamics Insight into the Diverse Thermodynamic Behavior of a Beta-Hairpin Peptide
(2013-07-01)
Tsai, Min-Yeh
;
Yuan, Jian-Min
;
Yamaki, Masahiro
;
Lin, Chih-Kai
;
Lin, Sheng Hsien
The b-hairpin is a building block in the -sheet structure. Understanding the formation of the -hairpin may provide insight into the formation of -sheet structures in, for example, protein amyloids. In this study, we performed molecular dynamics (MD) simulations to investigate the temperature-dependent transition behaviors of the GB1 -hairpin peptide. The simulated results are analysed in terms of distances between pairs of peptide bonds and site-dependent dihedral angles. Our results show that the properties of the hairpin can be site-dependent and that the dependency is primarily associated with the hairpin's geometrical shape and specific interactions, such as hydrophobic clustering. Thus our study provides a foundation for the interpretation of probe-dependent experimental results.
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 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.
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.
Quantum Switching of pi-Electron Rotations in a Nonplanar Chiral Molecule by Using Linearly Polarized UV Laser Pulses
(2012-09-05)
Mineo, Hirobumi
;
Yamaki, Masahiro
;
Teranishi, Yoshiaki
;
Hayashi, Michitoshi
;
Lin, Sheng Hsien
Nonplanar chiral aromatic molecules are candidates for use as building blocks of multidimensional switching devices because the pi electrons can generate ring currents with a variety of directions. We employed (P)-2,2'-biphenol because four patterns of pi-electron rotations along the two phenol rings are possible and theoretically determine how quantum switching of the it-electron rotations can be realized. We found that each rotational pattern can be driven by a coherent excitation of two electronic states under two conditions: one is the symmetry of the electronic states and the other is their relative phase. On the basis of the results of quantum dynamics simulations, we propose a quantum control method for sequential switching among the four rotational patterns that can be performed by using ultrashort overlapped pump and dump pulses with properly selected relative phases and photon polarization directions. The results serve as a theoretical basis for the design of confined ultrafast switching of ring currents of nonplanar molecules and further current-induced magnetic fluxes of more sophisticated systems.
The generation of stationary pi-electron rotations in chiral aromatic ring molecules possessing non-degenerate excited states
(2016-01-21)
Yamaki, Masahiro
;
Teranishi, Yoshiaki
;
Nakamura, Hiroki
;
Lin, Sheng Hsien
;
Fujimura, Yuichi
The electron angular momentum is a fundamental quantity of high-symmetry aromatic ring molecules and finds many applications in chemistry such as molecular spectroscopy. The stationary angular momentum or unidirectional rotation of pi electrons is generated by the excitation of a degenerated electronic excited state by a circularly-polarized photon. For low-symmetry aromatic ring molecules having non-degenerate states, such as chiral aromatic ring molecules, on the other hand, whether stationary angular momentum can be generated or not is uncertain and has not been clarified so far. We have found by both theoretical treatments and quantum optimal control (QOC) simulations that a stationary angular momentum can be generated even from a low-symmetry aromatic ring molecule. The generation mechanism can be explained in terms of the creation of a dressed-state, and the maximum angular momentum is generated by the dressed state with an equal contribution from the relevant two excited states in a simple three-electronic state model. The dressed state is formed by inducing selective nonresonant transitions between the ground and each excited state by two lasers with the same frequency but having different polarization directions. The selective excitation can be carried out by arranging each photon-polarization vector orthogonal to the electronic transition moment of the other transition. We have successfully analyzed the results of the QOC simulations of (P)-2,2\'-biphenol of axial chirality in terms of the analytically determined optimal laser fields. The present findings may open up new types of chemical dynamics and spectroscopy by utilizing strong stationary ring currents and current-induced magnetic fields, which are created at a local site of large compounds such as biomolecules.