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  • 151.
    Velichkova, Polina
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Himo, Fahmi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Theoretical study of the methyl transfer in guanidinoacetate methyltransferase2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 1, p. 16-19Article in journal (Refereed)
    Abstract [en]

    The reaction mechanism of the guanidinoacetate methyltransferase (GAMT) enzyme has been investigated by means of density functional theory using the B3LYP hybrid functional. GAMT catalyzes the S-adenosyl-l-methionine (SAM)-dependent methylation of guanidinoacetate (GAA) to form creatine. A quantum chemical model was built on the basis of the recent crystal structure of GAMT complexed with S-adenosylhomocysteine (SAH) and GAA. The methyl group transfer from SAM to NE of GAA is shown to occur concertedly with a proton transfer from NE to the neighboring OD1 of Asp134. Good agreement is found between the calculated barrier and the experimental rate.

  • 152. Villa, Alessandra
    et al.
    Hess, Berk
    Max-Planck-Institute for Polymer Research, Mainz, Germany.
    Saint-Martin, Humberto
    Dynamics and structure of Ln(III)-aqua ions: a comparative molecular dynamics study using ab initio based flexible and polarizable model potentials2009In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 20, p. 7270-7281Article in journal (Refereed)
    Abstract [en]

    Aqueous solutions of a light (Nd3+), a middle (Gd3+), and a heavy (Yb3+) lanthanide ion were studied using ab initio based flexible and polarizable analytical potentials in classical molecular dynamics simulations to describe their thermodynamic, structural, and dynamic features. To avoid the spurious demise of O-H bonds, it was necessary to reparametrize an existing water model, which resulted in an improved description of pure water. The good agreement of the results from the simulations with the experimental hydration enthalpies, the Ln(III)-water radial distribution functions, and the water-exchange rates validated the potentials, though the r(Ln-Ow) distances were 6% longer than the experimentally determined values. A nona-coordinated state was found for Nd3+ in 95% of the simulation, with a tricapped trigonal prism (TCTP) geometry; the corresponding water-exchange mechanism was found to be of dissociative interchange (Id) character through a short-lived octa-coordinated transition state in a square antiprism (SQA) geometry. An octa-coordinated state in SQA geometry was found for Yb3+ in 99% of the simulation, and the observed exchange events exhibited characteristics of an interchange (I) mechanism. For Gd3+ an equilibrium was observed between 8-fold SQA and 9-fold TCTP coordinated states that was maintained by the frequent exchange of a water molecule from the first hydration shell with the bulk, thus producing significant deviations from the ideal geometries, and a fast exchange rate. Though strong water-water interactions prevented a full alignment of the dipoles to the ion's electric field, the screening was found large enough as to limit its range to 5 A; water molecules further apart from the ion were found to have the same dipole as the molecules in the bulk, and a random orientation. The interplay among the water-ion and the water-water interactions determined the different coordination numbers and the different dynamics of the water exchange in the first hydration shell for each ion.

  • 153. Wang, Y. -L
    et al.
    Sarman, S.
    Glavatskih, Sergei B.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Antzutkin, O. N.
    Rutland, M. W.
    Laaksonen, A.
    Atomistic insight into tetraalkylphosphonium-bis(oxalato)borate ionic liquid/water mixtures. I. Local microscopic structure2015In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 119, no 16, p. 5251-5264Article in journal (Refereed)
    Abstract [en]

    Atomistic simulations have been performed to investigate the microscopic structural organization of aqueous solutions of trihexyltetradecylphosphonium bis(oxalato)borate ([P<inf>6,6,6,14</inf>][BOB]) ionic liquid (IL). The evolution of the microscopic liquid structure and the local ionic organization of IL/water mixtures as a function of the water concentration is visualized and systematically analyzed via radial and spatial distribution functions, coordination numbers, hydrogen bond network, and water clustering analysis. The microscopic liquid structure in neat IL is characterized by a connected apolar network composed of the alkyl chains of [P<inf>6,6,6,14</inf>] cations and isolated polar domains consisting of the central segments of [P<inf>6,6,6,14</inf>] cations and [BOB] anions, and the corresponding local ionic environment is described by direct contact ion pairs. In IL/water mixtures with lower water mole fractions, the added water molecules are dispersed and embedded in cavities between neighboring ionic species and the local ionic structure is characterized by solvent-shared ion pairs through cation-water-anion triple complexes. With a gradual increase in the water concentration in IL/water mixtures, the added water molecules tend to aggregate and form small clusters, intermediate chain-like structures, large aggregates, and eventually a water network in water concentrated simulation systems. A further progressive dilution of IL/water mixtures leads to the formation of self-organized micelle-like aggregates characterized by a hydrophobic core and hydrophilic shell consisting of the central polar segments in [P<inf>6,6,6,14</inf>] cations and [BOB] anions in a highly branched water network. The striking structural evolution of the [P<inf>6,6,6,14</inf>][BOB] IL/water mixtures is rationalized by the competition between favorable hydrogen bonded interactions and strong electrostatic interactions between the polar segments in ionic species and the dispersion interactions between the hydrophobic alkyl chains in [P<inf>6,6,6,14</inf>] cations. © 2015 American Chemical Society.

  • 154. Wang, Yong-Lei
    et al.
    Shah, Faiz Ullah
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Ghent University, Belgium .
    Antzutkin, Oleg N.
    Laaksonen, Aatto
    Atomistic Insight into Orthoborate-Based Ionic Liquids: Force Field Development and Evaluation2014In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 29, p. 8711-8723Article in journal (Refereed)
    Abstract [en]

    We have developed an all-atomistic force field for a new class of halogen-free chelated orthoborate-phosphonium ionic liquids. The force field is based on an AMBER framework with determination of force field parameters for phosphorus and boron atoms, as well as refinement of several available parameters. The bond and angle force constants were adjusted to fit vibration frequency data derived from both experimental measurements and ab initio calculations. The force field parameters for several dihedral angles were obtained by fitting torsion energy profiles deduced from ab initio calculations. To validate the proposed force field parameters, atomistic simulations were performed for 12 ionic liquids consisting of tetraalkylphosphonium cations and chelated orthoborate anions. The predicted densities for neat ionic liquids and the [P-6,P-6,P-6,P-14][BOB] sample, with a water content of approximately 2.3-2.5 wt %, are in excellent agreement with available experimental data. The potential energy components of 12 ionic liquids were discussed in detail. The radial distribution functions and spatial distribution functions were analyzed and visualized to probe the microscopic ionic structures of these ionic liquids. There are mainly four high-probability regions of chelated orthoborate anions distributed around tetraalkylphosphonium cations in the first solvation shell, and such probability distribution functions are strongly influenced by the size of anions.

  • 155.
    Wang, Yong-Lei
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Shimpi, Manishkumar R.
    Sarman, Sten
    Antzutkin, Oleg N.
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). Univ Ghent, Belgium.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Laaksonen, Aatto
    Atomistic Insight into Tetraalkylphosphonium Bis(oxalato)borate Ionic Liquid/Water Mixtures. 2. Volumetric and Dynamic Properties2016In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, no 30, p. 7446-7455Article in journal (Refereed)
    Abstract [en]

    Atomistic molecular dynamics simulations have been performed to investigate volumetric quantities and dynamic properties of binary trihexyltetradecylphosphonium bis(oxalato)-borate ([P-6,P-6,P-6,P-14][BOB]) ionic liquid (IL)/water mixtures with different water concentrations. The predicted liquid densities for typical [P-6,P-6,P-6,P-14][BOB] IL/water mixtures are consistent with available experimental data with a relative discrepancy of less than 3%. The liquid densities and excess molar volumes of all studied [P-6,P-6,P-6,P-14][BOB] IL/water mixtures are characterized by concave and convex features, respectively, within full water concentration range. The dynamic properties of [P-6,P-6,P-6,P-14] cations, [BOB] anions, and water molecules are particularly analyzed through calculation of velocity autocorrelation functions, diffusion coefficients, and reorientational autocorrelation functions and correlation times. The translational and reorientational mobilities of three species become faster upon increasing water concentration in [P-6,P-6,P-6,P-14][BOB] IL/water mixtures and present complex dynamical characteristics arising from three distinct microscopic diffusion features within the full water concentration range. The obtained striking volumetric quantities and particular dynamic properties are well correlated to microscopic liquid structural organization and distinct local ionic environment of all studied [P-6,P-6,P-6,P-14][BOB] IL/water mixtures.

  • 156. Wennmalm, Stefan
    et al.
    Rigler, Rudolf
    On Death Numbers and Survival Times of Single Dye Molecules1999In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207Article in journal (Refereed)
  • 157.
    Westerberg, Staffan
    et al.
    KTH, Superseded Departments, Electrum Laboratory.
    Wang, C
    Chou, K
    Somorjai, G A
    High-pressure ammonia adsorption and dissociation on clean Fe(111) and oxygen-precovered Fe(111) studied by sum frequency generation vibrational spectroscopy2004In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, no 20, p. 6374-6380Article in journal (Refereed)
    Abstract [en]

    The adsorption of gases N-2, H-2, O-2, and NH3 that play a role in ammonia synthesis have been studied on the Fe(111) crystal surface by Sum Frequency Generation (SFG) vibrational spectroscopy using an integrated ultrahigh vacuum/higla-pressure system. SFG spectra are presented for the dissociation intermediates, NH2 (similar to3325 cm(-1)) and NH (similar to3235 cm(-1)) under high pressure of ammonia (200 Torr) on the clean Fe(111) surface. Addition of 0.5 Torr of oxygen to 200 Torr of ammonia does not significantly change the bonding of dissociation intermediates to the surface. However, it leads to a phase change of nearly 180degrees between the resonant and nonresonant second-order nonlinear susceptibility of the surface, demonstrated as a reversal of the SFG spectral features. Heating the surface in the presence of 200 Torr of ammonia and 0.5 Torr of oxygen reduces the oxygen coverage, which can be seen from the SFG spectra as another relative phase change of 180degrees. The reduction of the oxide is also supported by Auger electron spectroscopy. The result suggests that the phase change of the spectral features could serve as a sensitive indicator of the chemical environment of the adsorbates. Clean Fe(111) is found to have a large SFG nonresonant signal. The magnitude of the nonresonant signal was dependent on the adsorption species; O-2 and N-2 decrease, while H-2 and NH3 increase the SFG nonresonant signal. The change in nonresonant signal is correlated to the change in work function for Fe(111) upon adsorption. Adsorption-induced changes in the SFG nonresonant signal was used as an indicator of surface conditions and to monitor surface reactions.

  • 158. Wiberg, Joanna
    et al.
    Marinado, Tannia
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagberg, Daniel P.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Albinsson, Bo
    Distance and Driving Force Dependencies of Electron Injection and Recombination Dynamics in Organic Dye-Sensitized Solar Cells2010In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 114, no 45, p. 14358-14363Article in journal (Refereed)
    Abstract [en]

    A series of dyes based on a triphenylamine donor and a rhodanine acetic acid anchor/acceptor for solar cell application has been studied with regards to electron injection and recombination kinetics using femtosecond transient absorption The series contains three dyes, with estimated electron transfer distances ranging from 17 2 to 11 0 angstrom and which have shown significant differences in energy conversion efficiencies The injection and recombination kinetics were studied in the NIR region where electrons in the conduction band of the TiO2 are suggested to absorb For all dyes, the injection rate is larger than (200 fs)(-1) which implicates a quantitative injection efficiency Surprisingly, the subsequent recombination reaction has a rate that increases with increasing linker length On the other hand, this behavior is consistent with the concomitant decrease in driving force for this series of dyes Moreover, the lifetimes show exponential distance dependence when corrected for driving force and reorganization energy, which indicates a superexchange interaction between the electrons in TiO2 and the radical cations of the dyes A dependence on probe wavelength of the attenuation factor was found giving a beta value of 0 38 angstrom(-1) at 940 nm and 0 49 angstrom(-1) at 1040 nm The difference is suggested to be due to the difference in electronic coupling between fully separated dye cations and injected electrons versus geminate electron-hole pairs Addition of tert butylpyridine, which from previous work is known to give a substantial drop in the IPCE values for the studied dyes, was found to decrease the amount of long-lived electrons in the TiO2 without affecting the injection rate

  • 159.
    Wohlert, Jakob
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Vapor Pressures and Heats of Sublimation of Crystalline beta-Cellobiose from Classical Molecular Dynamics Simulations with Quantum Mechanical Corrections2014In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 20, p. 5365-5373Article in journal (Refereed)
    Abstract [en]

    In this paper, we report the calculation of the enthalpy of sublimation, Delta H-sub, as a function of temperature of crystalline beta-cellobiose from molecular dynamics (MD) simulations, using two popular carbohydrate force fields. Together with the entropy difference between the solid and the vapor, AS, evaluated at atmospheric pressure, Delta H-sub gives the vapor pressure of cellobiose over the solid phase as a function of T. It is found that when quantum mechanical corrections to the enthalpy calculated from the distribution of normal modes is applied both force fields give Delta H-sub close to experiments. The entropy change, Delta S, which is calculated within a harmonic approximation becomes too small, leading to vapor pressures that are too low. These findings are relevant to MD simulations of crystalline carbohydrates in general, e.g., native cellulose.

  • 160.
    Xu, Hao
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Li, Li
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Manneberg, Otto
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Russom, Aman
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Gylfason, Kristinn B.
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Modulated fluorescence of colloidal quantum dots embedded in a porous alumina membrane2013In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 177, no 45, p. 14151-14156Article in journal (Refereed)
    Abstract [en]

    The fluorescence spectrum of CdSe core-CdS/ZnS shell colloidal quantum dots (QDs) embedded in porous alumina membrane was studied. Small peaks, superimposed on the principal QD fluorescence spectrum, were observed. Finite-difference time-domain simulation indicates that the QD point radiation emitting from within the membrane is strongly modulated by the photonic band structure introduced by the membrane pores, leading to the observed fine spectral features. Moreover, the principal QD fluorescence peak red-shifted when the optical excitation power was increased, which is attributed to QD material heating due to emitted phonons when the photoexcited electron and hole relax nonradiatively from high-energy states to the ground exciton state before fluorescence.

  • 161.
    Yang, Guomin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Holmboe, Michael
    Umeå University.
    Atomistic simulations of cation hydration in sodium and calcium montmorillonite nanopores2017In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 147, no 8, article id 084705Article in journal (Refereed)
    Abstract [en]

    facile synthesis of 3d-metal based electro-catalysts directly incorporated into a carbon support was carried out by.-radiation. Transition metals of period 4, i.e. Ni and Co, were precipitated and reduced from their respective salt solutions. The obtained materials were characterized by XRD, SEM, SQUID and the BET methods. Thereafter, the electrodes for fuel cells were fabricated out of synthesized material and their electrochemical performance for the oxygen reduction reaction in 6 M KOH was measured. Although the concentrations of Co and Ni in the electrode material were low (3.4% Co and 0.4% Ni) after reduction by irradiation, both the Ni and Co-based gas diffusion electrodes showed high catalytic activity for oxygen reduction both at room temperature and at 60 degrees C.

  • 162. Zalesny, Robert
    et al.
    Murugan, N. Arul
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tian, Guangjun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Medved, Miroslav
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    First-Principles Simulations of One- and Two-Photon Absorption Band Shapes of the Bis(BF2) Core Complex2016In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, no 9, p. 2323-2332Article in journal (Refereed)
    Abstract [en]

    Motivated by the outstanding properties of bis(BF2) core complexes as fluorophore probes, we present a systematic computational study of their vibrationally resolved one- and two-photon absorption spectra in vacuum and in solution. Electronic and vibrational structure calculations were performed using the coupled cluster CC2 method and the Kohn-Sham formulation of density functional theory (DFT). A nonempirical estimation of the inhomogeneous broadening, accomplished using the polarizable embedding (PE) approaches combined with time-dependent DFT and CC2 methods, is used as a key ingredient of the computational protocol employed for simulations of the spectral features in solution. The inhomogeneous broadening is also determined based on the Marcus theory employing linear response and state-specific polarizable continuum model (PCM) methods. It is found that the polarizable embedding CC2 and the state-specific PCM are the most successful approaches for description of environmental broadening. For the 1(1)A(g) -> 1(1)B(u) transition, the non-Condon effects can be safely neglected and a fair agreement between the simulated and experimental band shapes is found. In contrast, the shape of the vibrationally resolved band corresponding to the two-photon allowed 1(1)A(g) -> 2(1)A(g) transition is largely dominated by non-Condon effects. A generalized few-level model was also employed to analyze the mechanism of the electronic two-photon 1(1)A(g) -> 2(1)A(g) excitation. It was found that the most important optical channel involves the 1(1)B(u) excited state. Ramifications of the findings for general band shape modeling are briefly discussed.

  • 163.
    Zhang, Qiong
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Tu, Yaoquan
    Tian, He
    Zhao, Yan-Li
    Stoddart, J. Fraser
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Working Mechanism for a Redox Switchable Molecular Machine Based on Cyclodextrin: A Free Energy Profile Approach2010In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 114, no 19, p. 6561-6566Article in journal (Refereed)
    Abstract [en]

    This paper reports the working mechanism for a redox-responsive bistable [2]rotaxane incorporating an alpha-cyclodextrin (alpha-CD) ring (J. Am. Chem. Soc. 2008, 130, 11294-11296), based on free energy profiles obtained from all-atom molecular dynamics simulations. Employing an umbrella sampling technique, the free energy profiles (potential of mean force, PMF) were calculated for the shuttling motion of the alpha-CD ring between a tetrathiafulvalene (TTF) recognition site and a triazole (TZ) unit on the dumbbell of the rotaxane for three oxidation states (0, +1, +2) of the TTF unit. These calculated free energy profiles verified the experimentally observed binding preference for each state. Analysis of the free energy components reveals that, for these alpha-CD-based rotaxanes with charged TTF units, the real driving force for the shuttling in the oxidized states is actually the interactions between water and the rotaxane components, which overwhelms the attractive interactions between the alpha-CD ring and the charged dumbbell. In this work, we put forward a feasible approach to correctly describe the complexation behavior of CD with charged species, that is, free energy profiles obtained from all-atom molecular dynamics simulation.

  • 164. Zhang, Qiong
    et al.
    Tu, Yaoquan
    Tian, He
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Molecular dynamics simulations of polycarbonate doped with Lemke chromophores2007In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 111, no 36, p. 10645-10650Article in journal (Refereed)
    Abstract [en]

    In the search for optimal electro-optical modulating materials we report in this work molecular dynamics simulations of polycarbonate doped with Lemke chromophores which is a promising candidate system for materials with such functionality. The simulations cover the electric field poling effects on the chromophore order at a temperature above the glass transition temperature (T-g) of the material, the cooling procedure from liquid state to the glass state in the presence of the poling field, and the back relaxation of the system after removal of the field. Our study shows that electric field poling results in a higher chromophore order and that the order is also maintained during the cooling procedure with the poling field applied. In the liquid state, the applied poling field has little effect on the structure of the material. However, after the cooling procedure, the structure changes significantly because the polymer matrix tends to become closely packed. Our study thus indicates that for the bulk material, the structure of the host matrix is very important in determining the performance of the material.

  • 165.
    Zhao, Ke
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Liu, Peng-Wei
    Wang, Chuan-Kui
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Effects of Structural Fluctuations on Two-Photon Absorption Activity of Interacting Dipolar Chromophores2010In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 114, no 33, p. 10814-10820Article in journal (Refereed)
    Abstract [en]

    One- and two-photon absorption properties of organic chromophores consisting of interacting dipolar branches have been studied using density functional response theory in combination with molecular dynamics simulation. Effects of dipole interaction on optical absorptions have been examined. The importance of solvent effects on optical properties of charge-transfer states is explored by means of polarizable continuum model. It is found that for the interacting dipolar molecule with flexible conformations in solutions, the structural fluctuations can result in new spectral features or significant broadening of one-photon absorption spectrum. Our study highlights again the usefulness of the combined quantum chemical and molecular dynamics approach for modeling two-photon absorption materials in solutions.

  • 166.
    Zhao, Ke
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Tu, Yaoquan
    Luo, Yi
    Molecular Dynamics and Quantum Chemistry Study on Conformations and Optical Properties of Hydrogen Bonded Dipolar Merocyanine Dyes2009In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 30, p. 10271-10276Article in journal (Refereed)
    Abstract [en]

    An earlier proposed strategy to orient two merocyanine dyes in the desirable head-to-tail parallel fashion through multiple hydrogen bonds has been examined by molecular dynamics simulations and quantum chemical calculations. Two different merocyanine dyes dissolved in chloroform solution under various conditions are simulated by molecular dynamics. It is found that two dipolar units can be well connected through various numbers of hydrogen bonds. Although the probability to form the desirable head-to-tail dimer is unfortunately small even under strong poling electric field and low temperature, the formation of unwanted antiparallel structure has been effectively reduced. Typical hydrogen bonded dimers obtained from molecular dynamics simulations have been studied by hybrid density functional calculations. It is found that only the most probable complex can lead to the optical absorption spectrum that is in close agreement with the corresponding experiments. Calculated results for dipole moments of ground and charge transfer states, as well as first hyperpolarizabilities, of three typical complexes have also been provided.

  • 167.
    Zhao, Ke
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Yi, Luo
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Effects of Co-existing Isomers on Two-PhotonAbsorption of Organic Molecules in Solutions2010In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 114, no 41, p. 13167-13172Article in journal (Refereed)
    Abstract [en]

    Isomer-dependent two-photon absorption spectra Of organic molecules in solutions have been identified by time-dependent density functional theory calculations. Experimentally observed enhancements in two-photon absorptions of V-shaped hydroxypyrimidine derivatives are not due to the formation of molecular chillers but to mainly the co-occurrence of geometrical isomers. Solvent effects on both one- and two-photon absorption spectra have been carefully examined by using a supermolecular approach in combination with a polarizable continuum model. Special attention has been paid to understand the effects of hydrogen bonds on electronic structure and absorption spectra of these chromophores. Our calculated results are very helpful for understanding the corresponding experimental observations.

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