Browsing by Author "Hayashi, Michitoshi"

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A theoretical search for stable bent and linear structures of low-lying electronic states of the titanium dioxide (TiO(2)) molecule
(2011-01-01)
Lin, Chih-Kai
;
Li, Jun
;
Tu, Zheyan
;
Li, Xiangyuan
;
Hayashi, Michitoshi
In this work geometric optimization and potential energy surface (PES) scan for the TiO(2) molecule were carried out to find out possible stable structures by using quantum chemical calculations. The ground state (S(0) 1 (1)A(1)) has the only equilibrium with a symmetric bent structure, whereas the linear conformer is unstable. The first singlet excited state (S(1) 1 (1)B(2)), on the other hand, possesses two potential minima where one is bent around the Franck-Condon region and the other is linear. The second singlet excited state (S(2) 1 (1)A(2)) has only one minimum which is linear, and at which geometry the first two excited states degenerate. Other low-lying singlet and triplet excited states have been investigated accordingly. Among the functionals applied in the present DFT calculations, B3LYP gave results most close to available experimental data, while some recently developed ones including HSE06, omega B97X-D and CAM-B3LYP were not satisfactory for this small system. Ab initio methods such as CASSCF, CASPT2 as well as CCSD-related calculations have been applied, and the latter two showed good results similar to DFT/B3LYP.
A theoretical search for stable bent and linear structures of low-lying electronic states of the titanium dioxide (TiO2) molecule
(2011-01-01)
Lin, Chih-Kai
;
Li, Jun
;
Tu, Zheyan
;
Li, Xiangyuan
;
Hayashi, Michitoshi
In this work geometric optimization and potential energy surface (PES) scan for the TiO2 molecule were carried out to find out possible stable structures by using quantum chemical calculations. The ground state (S-0 1 (1)A(1)) has the only equilibrium with a symmetric bent structure, whereas the linear conformer is unstable. The first singlet excited state (S-1 1 B-1(2)), on the other hand, possesses two potential minima where one is bent around the Franck-Condon region and the other is linear. The second singlet excited state (S-2 1 (1)A(2)) has only one minimum which is linear, and at which geometry the first two excited states degenerate. Other low-lying singlet and triplet excited states have been investigated accordingly. Among the functionals applied in the present DFT calculations, B3LYP gave results most close to available experimental data, while some recently developed ones including HSE06, omega B97X-D and CAM-B3LYP were not satisfactory for this small system. Ab initio methods such as CASSCF, CASPT2 as well as CCSD-related calculations have been applied, and the latter two showed good results similar to DFT/B3LYP.
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
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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.
Atomistic nucleation sites of Pt nanoparticles on N-doped carbon nanotubes
(2013)
Sun, Chia-Liang
;
Pao, Chih-Wen
;
Tsai, Huang-Ming
;
Chiou, Jau-Wern
;
Ray, Sekhar C.
The atomistic nucleation sites of Pt nanoparticles (Pt NPs) on N-doped carbon nanotubes (N-CNTs) were investigated using C and N K-edge and Pt L-3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) spectroscopy. Transmission electron microscopy and XANES/EXAFS results revealed that the self-organized Pt NPs on N-CNTs are uniformly distributed because of the relatively high binding energies of the adsorbed Pt atoms at the imperfect sites. During the atomistic nucleation process of Pt NPs on N-CNTs, stable Pt-C and Pt-N bonds are presumably formed, and charge transfer occurs at the surface/interface of the N-CNTs. The findings in this study were consistent with density functional theory calculations performed using cluster models for the undoped, substitutional-N-doped and pyridine-like-N-doped CNTs.
Intrinsic coordination for revealing local structural changes in protein folding-unfolding
(2016-01-28)
Shiu, Ying-Jen
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Hayashi, Michitoshi
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Shih, Orion
;
Su, Charlene
;
Tsai, Min-Yeh
With a deformed object of a rigid rod inside, the local dislocations may be tracked relatively easily with respect to the internal rigid rod. We apply this concept on protein folding-unfolding to track the internal structural changes of an unfolded protein in solution. Proposed here is a protein internal coordination based on the major axis X of an ellipsoidal protein and the stable intrinsic transition dipole moment mu of the protein during unfolding. In this methodology, small-angle X-ray scattering (SAXS) is used to provide the protein global morphologies in the native and unfolded states. Furthermore, time-resolved fluorescence anisotropy (TRFA) provides the relative orientation between X and mu of Trp59 of the model protein cytochrome c. Hence observed in the protein unfolding with denaturants, acid, urea, or GuHCl, is the elongation of the native protein conformation along a reoriented protein major axis; accompanied are the different extents of relocations of the terminal a helices and loop structures of the protein in the corresponding unfolding.
Intrinsic Ultralow-Threshold Laser Action from Rationally Molecular Design of Metal-Organic Framework Materials
(2020-08-12)
Bera, Krishna Prasad
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Kamal, Saqib
;
Inamdar, Arif I.
;
Sainbileg, Batjargal
;
Lin, Hung-, I
Metal-organic frameworks (MOFs) are superior for multiple applications including drug delivery, sensing, and gas storage because of their tunable physiochemical properties and fascinating architectures. Optoelectronic application of MOFs is difficult because of their porous geometry and conductivity issues. Recently, a few optoelectronic devices have been fabricated by a suitable design of integrating MOFs with other materials. However, demonstration of laser action arising from MOFs as intrinsic gain media still remains challenging, even though some studies endeavor on encapsulating luminescence organic laser dyes into the porous skeleton of MOFs to achieve laser action. Unfortunately, the aggregation of such unstable laser dyes causes photoluminescence quenching and energy loss, which limits their practical application. In this research, unprecedently, we demonstrated ultralow-threshold (similar to 13 nJ/cm(2)) MOF laser action by a judicious choice of metal nodes and organic linkers during synthesis of MOFs. Importantly, we also demonstrated that the white random lasing from the beautiful microflowers of organic linkers possesses a porous network, which is utilized to synthesize the MOFs. The highly luminescent broad-band organic linker 1,4-NDC, which itself exhibits a strong white random laser, is used not only to achieve the stimulated emission in MOFs but also to reduce the lasing threshold. Such white lasing has multiple applications from bioimaging to the recently developed versatile Li-Fi technology. In addition, we showed that the smooth facets of MOF microcrystals can show Fabry-Perot resonant cavities having a high quality factor of similar to 10(3) with excellent photostability. Our unique discovery of stable, nontoxic, high-performance MOF laser action will open up a new route for the development of new optoelectronic devices.
Mesostructured Arrays of Nanometer-spaced Gold Nanoparticles for Ultrahigh Number Density of SERS Hot Spots
(2014-05-01)
Lai, Ying-Huang
;
Chen, Shiaw-Woei
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Hayashi, Michitoshi
;
Shiu, Ying-Jen
;
Huang, Chiao-Cheng
A novel one-trough synthesis via an air-water interface is demonstrated to provide hexagonally packed arrays of densely spaced metallic nanoparticles (NPs). In the synthesis, a mesostructured polyoxometalate (POM)-silicatropic template (PSS) is first self-assembled at the air-water interface; upon UV irradiation, anion exchange cycles enable the free-floating PSS film to continuously uptake gold precursors from the solution subphase for diffusion-controlled and POM-site-directed photoreduction inside the silica channels. NPs approximate to 2 nm can hence be homogeneously formed inside the silica-surfactant channels until saturation. As revealed via X-ray diffraction, small-angle X-ray scattering (SAXS), grazing incidence SAXS, and transmission electron microscopy, the Au NPs directed by the PSS template are arrayed into a 2D hexagonal lattice with inter-channel spacing of 3.2 nm and a mean along-channel NP spacing of 2.8 nm. This corresponds to an ultra-high number density (approximate to 10(19) NPs cm(-3)) of narrowly spaced Au NPs in the Au-NP@PSS composite, leading to 3D densely deployed hot-spots along and across the mesostructured POM-silica channels for surface-enhanced Raman scattering (SERS). Consequently, the Au-NP@PSS composite exhibits prominent SERS with 4-mercaptobenzoic acid (4-MBA) adsorbed onto Au NPs. The best 4-MBA detection limit is 5 nm, with corresponding SERS enhancement factors above 10(8).
Quantum Chemistry Study on Internal Conversion of Diphenyldibenzofulvene in Solid Phase
(2011-12-22)
Li, Ming-Chung
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Hayashi, Michitoshi
;
Lin, Sheng-Hsien
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應用化學系
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Department of Applied Chemistry
We investigate the nonradiative decay process of diphenyldibenzofulvene (DPDBF) in solid phase by using the quantum chemistry methods. To carry out the nonradiative rate constant calculation, we construct a solid phase model based on the ONIOM method. The geometry of the DPDBF molecule is optimized for the ground state by DFT and the first excited state by TD-DFT, and the corresponding vibrational frequencies and normal coordinates are computed. Under displaced-distorted harmonic oscillator potential approximation, Huang-Rhys factors are obtained. Vibronic coupling constants are calculated as a function of the normal mode based on Domcke's scheme. We find that vibronic coupling constants of 12 modes with large reorganization energies are of similar order, and if this result is still valid for other modes, the internal conversion rate would be determined by high frequency modes because they have a significant nuclear factor that is related to Franck-Condon overlap intergrals. We also find that geometrical changes are suppressed due to the stacking effect, which yields small Huang-Rhys values in the solid phase.
Quantum Localization of Coherent pi-Electron Angular Momentum in (P)-2,2 '-Biphenol
(2014-06-05)
Yamaki, Masahiro
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Mineo, Hirobumi
;
Teranishi, Yoshiaki
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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
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Yamaki, Masahiro
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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.
Spectroscopic Study of Organic Light-emitting Polymers: A Review
(2010)
Chang, Railing
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Hayashi, Michitoshi
;
Lin, S. H.
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應用化學系
;
Department of Applied Chemistry
In this review paper, we theoretically investigate the optical properties of the organic light-emitting polymer (OLEP) Despite of its enormous size, OLEP is described well by the oligomer model because of the imperfect backbone structure. By using the molecular exciton theory, we calculate the energy level of S(1) states and Huang-Rhys factor of oligomer which decrease with its chain length The spectral profiles for oligomer thus can be readily calculated and used to explain the absorption and PL for OLEP in dilute solution with a chain length distribution described by a Gaussian function Moreover we show that the luminescence of OLEP in high concentration solution as well as thin film is mainly contributed by the interchain states In the ultrafast time-resolved PL spectrum, we propose a model in which the dynamic processes such as energy transfer, charge transfer, and vibrational relaxation are treated in an equal-footing manner, and find that in the high energy region the states in a thin film of OLEP is dominated by the intrachain species In addition, we discuss the nonradiative transitions occurring in OLEP
Theoretical formulation and computational simulation of electronic sum-frequency generation (ESFG) spectroscopy of surfactant on water surface
(2014-03-16)
Lin, Chih-Kai
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Hayashi, Michitoshi
;
Lin, Sheng Hsien
;
應用化學系
;
Department of Applied Chemistry
Theoretical Formulation and Simulation of Electronic Sum-Frequency Generation Spectroscopy
(2013-11-14)
Lin, Chih-Kai
;
Hayashi, Michitoshi
;
Lin, Sheng Hsien
;
應用化學系
;
Department of Applied Chemistry
Sum-frequency generation (SFG) spectroscopy is a powerful tool for not only identifying molecular species but also analyzing orientation configurations on a surface/interface. In this Article, we presented reformulation of the theoretical framework of electronic SFG spectroscopy, the signal of which could be greatly enhanced by tuning one or two incident beam frequencies resonant with electronic excited states. Simulated electronic SFG spectra resonant at the sum frequency of a pair of coumarin-derivative pH-indicator surfactant molecules, 4-methyl-7-hydroxycoumarin and its anionic counterpart (MHC/MHC-), floating on the water surface were carried out as a demonstration.
Theoretical studies on the absorption spectra of cis-[Ru(4,4 \'-COO-2,2 \'-bpy)(2)(X)(2)](4-), (X = NCS, Cl) and panchromatic trans-terpyridyl Ru complexes including strong spin-orbit coupling
(2015-01-01)
Mishima, Kenji
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Kinoshita, Takumi
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Hayashi, Michitoshi
;
Jono, Ryota
;
Segawa, Hiroshi
In this paper, we theoretically and experimentally investigate the photophysical and chemical characteristics and absorption spectra of various ruthenium complexes in solution used as efficient dye-sensitized solar cells. The target molecules are two well-known complexes, cis-[Ru(4,4\'-COO-2,2\'-bpy)(2)(X)(2)](4-), (X = NCS, Cl) and trans-terpyridyl Ru. The experimental absorption spectra of these molecules, which show strong spin-orbit (SO) coupling, are simulated using first-order perturbation theory based on time-dependent density functional theory and quantum chemistry calculations. It turns out that the theory can simulate the experimental data very well, which indicates that SO coupling is very important and the mixing between singlet and triplet states is strong in these molecules because of the large SO coupling constant of the Ru atom. The exact absorption spectra can only be reproduced by including the perturbation by SO coupling. The physical and chemical differences between cis-[Ru(4,4\'-COO-2,2\'-bpy)(2)(X)(2)](4-), (X = NCS, Cl) and trans-terpyridyl Ru complexes are elucidated by natural bond orbital and natural transition orbital analyses. From these analyses, we have found that the two kinds of Ru complexes are quite different in terms of photoexcitation response and chemical bonding between the central Ru atom and the surrounding ligands.
Theoretical Study on Structure and Sum-Frequency Generation (SFG) Spectroscopy of Styrene-Graphene Adsorption System
(2013-01-31)
Lin, Chih-Kai
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Shih, Chun-Chi
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Niu, Yingli
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Tsai, Min-Yeh
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Shiu, Ying-Jen
In this theoretical study, we aimed to simulate the sum-frequency generation (SFG) spectroscopy of a thin polystyrene layer physically adsorbed on the graphene sheet and to figure out the orientation distribution of the phenyl units. To simplify the problem, we started the investigation by constructing molecular models with styrene and ethylbenzene monomers and styrene oligomers up to four units adsorbed on a finite-sized graphene hexagon. Geometric optimization results showed that the phenyl rings of the adsorbate always orientate close to the surface normal with a small tilt angle. The adsorption is weak but not negligible. SFG spectra have been simulated based on these calculated structures, vibrational frequencies, and dipole and polarizability derivatives to compare with experimental reports of polystyrene adsorbed on other surfaces.
Theoretical treatment of anharmonic effect on molecular absorption, fluorescence spectra, and electron transfer
(2009-03-30)
Zhu, Chaoyuan
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Liang, Kuo Kan
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Hayashi, Michitoshi
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Lin, Sheng Hsien
;
應用化學系分子科學碩博班
It is well-known that the mirror image between absorption and fluorescence spectra is held for the displaced harmonic-oscillator system, and also this mirror image is independent to the chiral symmetry in which the excited-state potential energy surface is right-handed or left-handed with respect to the ground-state potential energy surface. As the first-order approximation of anharmonic correction is added into the displaced harmonic oscillator, this mirror image is broken down, and then the spectra can be depended on the chiral symmetry mentioned above. Both absorption and fluorescence coefficients are derived analytically within the first-order anharmonic approximation and numerical test is carried out to demonstrate the breaking down of the mirror image. Based on the same analysis, the electron transfer rate is derived analytically within the first-order anharmonic approximation. This rate might take the form of Arrhenius's equation but not form of Marcus's equation. Furthermore, it is found that this rate is also depending on the chiral symmetry. (c) 2009 Elsevier B.V. All rights reserved.
Theoretical treatments of ultrafast electron transfer from adsorbed dye molecule to semiconductor nanocrystalline surface
(2006-10-21)
Liang, Kuo Kan
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Lin, Chih-Kai
;
Chang, Huan-Cheng
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Hayashi, Michitoshi
;
Lin, Sheng Hsien
In studying ultrafast electron transfer from a dye molecule to a nanosized semiconductor particle, pump-probe experiments are commonly used. In this system the electron transfer (ET) rate is faster than vibrational relaxation so that the ET rate should be described by a single-level rate constant and the probing signal (often in the form of time-resolved spectra) contains the contribution from the dynamics of both population and coherence (i.e., wave packet). In this paper, we shall present the theoretical treatments for femtosecond time-resolved pump-probe experiment and the dynamics of population and coherence by the density matrix method, and the calculation of single-level ET rate constant involved in a pump-probe experiment. As an application, we show the theoretical results using parameters extracted from experiments on a specific dye/semiconductor system. (c) 2006 American Institute of Physics.
Theory of time-resolved sum-frequency generation and its applications to vibrational dynamics of water
(2007-09-20)
Hayashi, Michitoshi
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Shiu, Ying-Jen
;
Liang, Kuo Kan
;
Lin, Sheng Hsien
;
Shen, Yuan Ron
A molecular theory of time-resolved sum-frequency generation (SFG) has been developed. The theoretical framework is constructed using the coupled-oscillator model in the adiabatic approximation. This theory can treat not only the vibrational spectroscopy but also vibrational dynamics. An application of this theory is also provided for estimation of the time constants of the intermolecular vibrational energy transfer between water molecules. This approach can be used for molecular analysis of the experimental results of Shen at al. on the SFG studies of vibrational dynamics of water.