Vibration-assisted coherent excitation energy transfer in a detuned dimer

The important role of high-energy intramolecular vibrational modes for excitation energy transfer in the detuned photosynthetic systems is studied. Based on a basic dimer model which consists of two two-level systems(pigments)coupled to high-energy vibrational modes, we find that the high-energy intramolecular vibrational modes can enhance the energy transfer with new coherent transfer channels being opened when the phonon energy matches the detuning between the two pigments. As a result, the energy can be effectively transferred into the acceptor. The effective Hamiltonian is obtained to reveal the strong coherent energy exchange among the donor, the acceptor, and the high-energy intramolecular.A semi-classical explanation of the phonon-assisted mechanism is also shown.     

Rectification effects in coherent transport through single molecules

A minimal model for coherent transport through a donor/acceptor molecular junction is presented. The two donor and acceptor sites are described by single levels energetically separated by an intramolecular tunnel barrier. In the limit of strong coupling to the electrodes a current rectification for different bias voltage polarities occurs. Contacts with recent experiments of molecular rectification are also given.     

Multicanonical Monte Carlo simulations on intramolecular micelle formation in copolymers

The formation of intramolecular micelles in copolymers with periodic sequence, where hydrophobic units (stickers) are periodically placed along the chain, is studied by using multicanonical Monte Carlo computer simulations for an off-lattice bead-rod model in three dimensions. With decreasing the temperature, a transition from random-coil conformations to micelles occurs and flower-type micelles are formed via the transition. The number of stickers forming a micelle core is limited by the excluded-volume effect of loop chains around micelle cores. By this effect, two intramolecular micelles are formed for long polymer chains with 60 bonds via the coil-to-micelle transition. By further decreasing the temperature, we find that another transition, i.e., a micelle-to-micelle transition, takes place. At this transition point, the two intramolecular micelles merge into one micelle. Furthermore, we extend the multicanonical MC method to study elastic properties of single polymer chains with strong attractive interactions under external force fields, and study how the intramolecular micellization affects the elastic property of single polymer chains.     

H2 intramolecular evolution

From the Madelung hydrodynamical formalism generalized to an heterogeneous population of electrons and nuclei, a non-adibatic quasi-classical local model (NAQCL) of a molecule is constructed. This provides a method to approach in a quasi-classical way intramolecular evolution with electronsnuclei coupling. A specific initial state for the hydrogen molecule is used to distinguish the results of the adiabatic and NAQCL analysis of intramolecular evolution induced by this state.     

Influence of intramolecular hydrogen bond formation sites on fluorescence mechanism

The fluorescence mechanism of HBT-HBZ is investigated in this work. A fluorescent probe is used to detect HClO content in living cells and tap water, and its structure after oxidation by HClO (HBT-ClO) is discussed based on the density functional theory (DFT) and time-dependent density functional theory (TDDFT). At the same time, the influence of the probe conformation and the proton transfer site within the excited state molecule on the fluorescence mechanism are revealed. Combined with infrared vibrational spectra and atoms-in-molecules theory, the strength of intramolecular hydrogen bonds in HBT-HBZ and HBT-ClO and their isomers are demonstrated qualitatively. The relationship between the strength of intramolecular hydrogen bonds and dipole moments is discussed. The potential energy curves demonstrate the feasibility of intramolecular proton transfer. The weak fluorescence phenomenon of HBT-HBZ in solution is quantitatively explained by analyzing the frontier molecular orbital and hole electron caused by charge separation. Moreover, when strong cyan fluorescence occurs in solution, the corresponding molecular structure should be HBT-ClO(T). The influence of the intramolecular hydrogen bond formation site on the molecule as a whole is also investigated by electrostatic potential analysis.     

JAHN-TELLER EFFECT AND SUPERCONDUCTING MECHANISM OF THE HOLE-DOPED C60 SOLID

A possible superconducting mechanism of the hole-doped C₆₀ solid is discussed. Under the assumption that the superconductivity results from the strong coupling between electrons at Fermi surface and intramolecular vibrations, a simple expression for the electron-phonon coupling parameter λ is derived. The related transition temperature is estimated and can be much greater than that of the alkali-metal-doped C₆₀ solid.     

Triplet exciton energy and the magnitude of the charge-transfer interaction inside dimers in the Alkali-TCNQ salts

The optical absorption spectra of several crystalline anion radiacal salts have been analyzed recently within the frame of the model Hamiltonian of electrons and intramolecular excitons and vibrations in the limit of strong interaction of the excitonic and vibrational motions with the unpaired electrons. In the present work the magnitude of the intermolecular charge transfer interaction inside dimers in the Alkali TCNQ salts is deduced from the knowledge of the experimental triplet exciton energy and the constants characterizing the electronic, excitonic and vibrational properties of TCNQ molecules. Perturbation calculation is used to derive a formula for the triplet exciton energy.     

Direct observation of radical intermediates during electron transfer between DNA and a ternary copper complex

The photoinduced electron transfer (PET) reaction within a ternary copper complex [Cu(phen)(Htrp)]⁺ (Htrp: l-tryptophanato; phen: 1,10-phenanthroline) (1) and in presence of DNA has been studied in homogeneous buffer medium and in reverse micelles. An intramolecular electron transfer occurs within the photoexcited complex (1) from tryptophan to phen. The copper complex can displace ethidium bromide from DNA backbone and on photoexcitation can oxidize DNA in a deoxygenated environment due to intermolecular electron transfer, although the intramolecular electron transfer is thermodynamically favorable. A prominent magnetic field effect (MFE) has been found even in homogeneous aqueous medium for the triplet born radicals both in case of intra and intermolecular electron transfer reactions. In case of intramolecular electron transfer the observation of MFE is similar to that of linked donor-acceptor system. However the observation of MFE for the intermolecular electron transfer between non-covalently bound complex-DNA systems is rather rare. Some non-covalent weak interaction, e.g. hydrophobic interaction between the phen ligand and DNA base pairs and electrostatic force of attraction between [Cu(phen)(Htrp)]⁺ complex and DNA may lead to partial intercalation of the copper complex within DNA that is responsible for such a rare observation.     

Effect of the electron-exciton and the electron-vibronic interactions in the absorption spectra of TCNQ salts

The energies and the relative intensities of the lines of the optical absorption spectra of a certain class of TCNQ salts are calculated within a strong coupling approximation. The unpaired electrons are supposed to interact strongly with the intramolecular excitons and with several modes of intramolecular vibrations. The agreement of the theory and experiment is satisfactory. The ways of possible improvements of the theory and the interpretation of the experimental data are discussed.     

A mathematical simulation of intramolecular proton phototransfer

A system of equations for the matrix elements of the density operator of a seven-level model molecule interacting with a light pulse was solved numerically to determine the time dependences of the populations of molecule states at various radiation pulse parameters and parameters characterizing radiative and nonradiative spontaneous molecule transitions and reversible transitions between some of its states. The results were used to characterize the photoisomerization of molecules between states with different positions of the proton of the intramolecular H-bond (the keto and enol forms). Examples of oscillating molecular state population modulation in isomer-isomer tunnel proton shifts are given. Changes in the development of photoionization in time as molecular parameters and radiation pulse width and intensity changed were considered. An analysis of the results obtained is an example of the use of mathematical simulation of intramolecular dynamics for increasing the effectiveness of using spectral-time data in the determination of the mechanism of proton phototransfer in molecules with intramolecular H-bonds     

On the role of intramolecular vibrational energy redistribution in infrared multiphoton excitation of polyatomic molecules

A model approach conceived to account for the processes of intramolecular vibrational energy redistribution (IVR) in the course of infrared multiphoton excitation (IRMPE) of polyatomic molecules is considered.     

Intramolecular bonding in a statistical associating fluid theory of ring aggregates

The first-order thermodynamic perturbation theory of Wertheim (TPT1) is extended to treat ring aggregates, formed by inter- and intramolecular association. The expression for the residual association contribution to the Helmholtz free energy for ring aggregates, incorporating the appropriate terms in Wertheim's fundamental graph sum of the TPT1 density expansion, is derived to calculate the distribution of the molecular bonding states. This requires the introduction of two new parameters to characterise each possible ring type: the ring size τ, which is equal to one in the case of intramolecular association, and a parameter W that captures the likelihood of two ring-forming sites bonding. The resulting framework can be incorporated in equations of state that account for the residual association contribution to the free energy, such as the statistical associating fluid theory (SAFT) family, or the cubic plus association (CPA) equation of state. This extends the applicability of these equations of state to mixtures with an arbitrary number of association sites capable of hydrogen bonding to form intramolecular and intermolecular rings. The formalism is implemented within SAFT-VR Mie to calculate the fluid-phase equilibria of model chain-like molecules containing two associating sites A and B, allowing for the formation of open-chain aggregates and intramolecular bonds. The effect of adding a second component that competes for the association sites that mediate intramolecular association in the chain is also examined. Accounting for intramolecular bonding is shown to have a significant impact on the phase equilibria of such systems.     

Solvent effects on radiationless transitions

A quantum mechanical theory of the solvent effect on radiationless transitions is developed within the framework of a dynamic coupling model. This model allows us to describe the solvent effect on any mechanism of intramolecular radiationless transition, in polar as well as non-polar solvents.     

On transformations of physical systems

A universal, unified theory of transformations of physical systems based on the propositions of probabilistic physics is developed. This is applied to the treatment of decay processes and intramolecular rearrangements. Some general features of decay processes are elucidated. A critical analysis of the conventional quantum theories of decay and of Slater's quantum theory of intramolecular rearrangements is given. It is explained why, despite the incorrectness of the decay theories in principle, they can give correct estimations of decay rate constants. The reasons for the validity of the Arrhenius formula for the temperature dependence of an intramolecular rearrangement rate constant are discussed. A criterion for the possibility of a proper intramolecular rearrangement is given. The issue of causality in quantum physics is settled.     

生物素和吡哆素的太赫兹光谱特性研究

采用傅里叶变换红外光谱技术(FTIR)和密度泛函理论(DFT)研究了常温环境下生物素和吡哆素两种维生素的太赫兹光谱特性,测量和理论分析的结果显示在太赫兹范围内,维生素分子内存在较强的分子内和分子间相互作用力。实验中样品与聚乙烯粉末按照不同的比例进行混合,结果表明样品所含比例越大,其在高频段的吸收谱重复性越差,这证实了维生素样品的吸收率随着频率升高逐渐增加。采用密度泛函理论(DFT)分析了生物素和吡哆素的单分子、二分子、三分子、以及晶胞分子的太赫兹光谱,指证了对应的吸收峰,阐明了分子内和分子间相互作用力的振动和转动机制。     

Development of a force field for molecular simulation of the phase equilibria of perfluoromethylpropyl ether

A first step towards the development of a general, realistic potential model for perfluoroether compounds has been to parameterize a united atom model for a short chain perfluoroether perfluoromethylpropyl ether (CF₃CF₂CF₂OCF₃). The potential model takes the usual form in which separate bond bending and torsional terms describe the intramolecular interactions with the addition of van der Waals and electrostatic terms to describe the non-bonded interactions. Ab initio quantum calculations have been carried out to obtain the partial charges and intramolecular torsional and bending potentials. Phase equilibrium data were then used to optimize the van der Waals interaction parameters through Gibbs ensemble Monte Carlo simulations. The resulting model reproduces vapour-liquid equilibrium densities, the critical temperature and the critical density of perfluoromethylpropyl ether, in good agreement with those from experiment.     

Raman scattering from mixed crystals (HgBr2)1−x(HgI2)x

The behavior of long wavelength optic phonons in mixed system HgBr₂-HgI₂ has been investigated in Raman scattering. Different types of behavior, i.e. ‘persistent type’ and ‘amalgamation type’ were observed. Three strong Raman bands were observed for persistent type mode. These correspond to stretching vibration of HgBr₂, HgBrI, HgI₂ molecules. Intensity of these bands showed striking concentration dependence. A model based on nearly free molecular approximation have been proposed to explain the dependence. The analysis indicated that the distribution of anions on the sublattices is essentially random. For amalgamation (one-mode) type behavior, it is suggested that the intramolecular force relevant to the vibration is comparable to the intermolecular force and that the band width of the corresponding phonon branch in the parent crystal is broad enough to be degenerate with impurity mode at the low concentration limit.     

Solitons in molecular systems with nonlinear nearest-neighbour interactions

The soliton theory of the motion of an extra electron (intramolecular excitation) in one-dimensional molecular structures with a strong electron (exciton)-phonon coupling is developed for a wide class of nonlinear (realistic) nearest-neighbour interactions which provide finite values of the soliton dynamical quantities at velocities less than or equal to that of sound.     

Intramolecular vibrational dynamical barrier due to extremely irrational couplings

The intramolecular vibrational dynamics due to extremely irrational couplings is demonstrated by contrast to the resonance couplings, for the three-mode case of H分子物理学 分子内振动弛豫 甚高频无理耦合 共鸣 振动动力学intramolecular vibrational relaxation, extremely irrational couplings, resonanceProject supported by the National Natural Science Foundation of China (Grant No~20373030) and the Foundation for Key Program of Ministry of Education, China (Grant No~306020) and the Specialized Research Fund for the Doctoral Program of Higher Educatio2007-03-04The intramolecular vibrational dynamics due to extremely irrational couplings is demonstrated by contrast to the resonance couplings, for the three-mode case of H2O as an example. The extremely irrational couplings are shown to impose such strong hindrance to intramolecular vibrational relaxation （IVR） that they act as barriers. They restrict the direct action/energy transfer between the two stretching modes, though they allow the transfer between a stretching and a bending modes. In contrast, the resonance is more mediated by the bending mode and leads to chaotic IVR. It is also shown that there is a region in the dynamical space in which resonance and extremely irrational couplings coexist.