kth.sePublications
Change search
Refine search result
1234567 1 - 50 of 728
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Aidas, Kestutis
    et al.
    Angeli, Celestino
    Bak, Keld L.
    Bakken, Vebjorn
    Bast, Radovan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Boman, Linus
    Christiansen, Ove
    Cimiraglia, Renzo
    Coriani, Sonia
    Dahle, Pal
    Dalskov, Erik K.
    Ekstrom, Ulf
    Enevoldsen, Thomas
    Eriksen, Janus J.
    Ettenhuber, Patrick
    Fernandez, Berta
    Ferrighi, Lara
    Fliegl, Heike
    Frediani, Luca
    Hald, Kasper
    Halkier, Asger
    Hattig, Christof
    Heiberg, Hanne
    Helgaker, Trygve
    Hennum, Alf Christian
    Hettema, Hinne
    Hjertenaes, Eirik
    Host, Stinne
    Hoyvik, Ida-Marie
    Iozzi, Maria Francesca
    Jansik, Branislav
    Jensen, Hans Jorgen Aa.
    Jonsson, Dan
    Jorgensen, Poul
    Kauczor, Joanna
    Kirpekar, Sheela
    Kjrgaard, Thomas
    Klopper, Wim
    Knecht, Stefan
    Kobayashi, Rika
    Koch, Henrik
    Kongsted, Jacob
    Krapp, Andreas
    Kristensen, Kasper
    Ligabue, Andrea
    Lutnaes, Ola B.
    Melo, Juan I.
    Mikkelsen, Kurt V.
    Myhre, Rolf H.
    Neiss, Christian
    Nielsen, Christian B.
    Norman, Patrick
    Olsen, Jeppe
    Olsen, Jogvan Magnus H.
    Osted, Anders
    Packer, Martin J.
    Pawlowski, Filip
    Pedersen, Thomas B.
    Provasi, Patricio F.
    Reine, Simen
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Ruden, Torgeir A.
    Ruud, Kenneth
    Rybkin, Vladimir V.
    Salek, Pawel
    Samson, Claire C. M.
    de Meras, Alfredo Sanchez
    Saue, Trond
    Sauer, Stephan P. A.
    Schimmelpfennig, Bernd
    Sneskov, Kristian
    Steindal, Arnfinn H.
    Sylvester-Hvid, Kristian O.
    Taylor, Peter R.
    Teale, Andrew M.
    Tellgren, Erik I.
    Tew, David P.
    Thorvaldsen, Andreas J.
    Thogersen, Lea
    Vahtras, Olav
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Watson, Mark A.
    Wilson, David J. D.
    Ziolkowski, Marcin
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    The Dalton quantum chemistry program system2014In: Wiley Interdisciplinary Reviews. Computational Molecular Science, ISSN 1759-0876, Vol. 4, no 3, p. 269-284Article in journal (Refereed)
    Abstract [en]

    Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree-Fock, Kohn-Sham, multiconfigurational self-consistent-field, MOller-Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from for a number of UNIX platforms.

  • 2. Aidas, Kestutis
    et al.
    Olsen, Jogvan Magnus H.
    Kongsted, Jacob
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Photoabsorption of Acridine Yellow and Proflavin Bound to Human Serum Albumin Studied by Means of Quantum Mechanics/Molecular Dynamics2013In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 117, no 7, p. 2069-2080Article in journal (Refereed)
    Abstract [en]

    Attempting to unravel mechanisms in optical probing of proteins, we have performed pilot calculations of two cationic chromophores-acridine yellow and proflavin-located at different binding sites within human serum albumin, including the two primary drug binding sites as well as a heme binding site. The computational scheme adopted involves classical molecular dynamics simulations of the ligands bound to the protein and subsequent linear response polarizable embedding density functional theory calculations of the excitation energies. A polarizable embedding potential consisting of point charges fitted to reproduce the electrostatic potential and isotropic atomic polarizabilities computed individually for every residue of the protein was used in the linear response calculations. Comparing the calculated aqueous solution-to-protein shifts of maximum absorption energies to available experimental data, we concluded that the cationic proflavin chromophore is likely not to bind albumin at its drug binding site I nor at its heme binding site. Although agreement with experimental data could only be obtained in qualitative terms, our results clearly indicate that the difference in optical response of the two probes is due to deprotonation, and not, as earlier suggested, to different binding sites. The ramifications of this finding for design of molecular probes targeting albumin or other proteins is briefly discussed.

  • 3.
    Aidas, Kestutis
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Kongsted, Jacob
    Laaksonen, Aatto
    Mocci, Francesca
    A quantum mechanics/molecular dynamics study of electric field gradient fluctuations in the liquid phase. The case of Na+ in aqueous solution2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 5, p. 1621-1631Article in journal (Refereed)
    Abstract [en]

    The Na-23 quadrupolar coupling constant of the Na+ ion in aqueous solution has been predicted using molecular dynamics simulations and hybrid quantum mechanics/molecular mechanics methods for the calculation of electric field gradients. The developed computational approach is generally expected to provide reliable estimates of the quadrupolar coupling constants of monoatomic species in condensed phases, and we show here that intermolecular polarization and non-electrostatic interactions are of crucial importance as they result in a 100% increased quadrupolar coupling constant of the ion as compared to a simpler pure electrostatic picture. These findings question the reliability of the commonly applied classical Sternheimer approximation for the calculations of the electric field gradient. As it can be expected from symmetry considerations, the quadrupolar coupling constants of the 5- and 6-coordinated Na+ ions in solution are found to differ significantly.

  • 4. Aldongarov, Anuar
    et al.
    Irgibaeva, Irina
    Hermansson, Kersti
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Theoretical study on passivation of small CdS clusters2014In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 112, no 5-6, p. 674-682Article in journal (Refereed)
    Abstract [en]

    We use density functional theory quantum chemical calculations to model optical properties of small cadmium sulphide clusters in order to explore the formation of trap states and the possibility to achieve surface passivation. The addition of capping oxygen ions on the surface of the CdS quantum dots is found to passivate the single-bonded Cd atoms. Added Cu ions resulted in the formation of deep trap states for certain locations of the copper impurity, while removal of single-bonded Cd atoms by adding S or SH groups leads to a band gap increase.

  • 5. Andersson, E.
    et al.
    Niskanen, Johannes
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Hedin, L.
    Eland, J. H. D.
    Linusson, P.
    Karlsson, L.
    Rubensson, J. -E
    Carravetta, V.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Feifel, R.
    Core-valence double photoionization of the CS2 molecule2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 9, p. 094305-Article in journal (Refereed)
    Abstract [en]

    Double photoionization spectra of the CS2 molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h nu=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2 pi(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C 1s)(-1)(2 pi(g))(-1) double vacancy.

  • 6. Andersson, E.
    et al.
    Stenrup, Michael
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Eland, J.H.D.
    Hedin, L.
    Berglund, M.
    Karlsson, L.
    Larson, Åsa
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rubensson, Jan Erik
    Feifel, Raimund
    Single-photon core-valence double ionization of molecular oxygen2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 78, no 2, p. 023409-Article in journal (Refereed)
    Abstract [en]

    Single-photon core-valence double ionization of molecular oxygen has been studied using a magnetic bottle time-of-flight electron coincidence spectrometer. The K-1 V-1 double ionization electron spectrum of O2 is reported and is assigned with the aid of ab initio calculations. A direct comparison of the core-valence double ionization electron spectra with the conventional valence band photoelectron spectrum is made. The lowest core-valence double ionization energy is found to be 571.6 eV and is associated with a Π3 dicationic state.

  • 7. Augustsson, A.
    et al.
    Kashtanov, Stepan
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Luo, Yi
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Chang, C.L.
    Ågren, Hans
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Rubensson, J.-E.
    Nordgren, J.
    Conformations and core-excitation dynamics liquid water.Manuscript (preprint) (Other academic)
  • 8. Baev, A.
    et al.
    Feifel, R.
    Gel'mukhanov, Faris
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Piancastelli, M. N.
    Bassler, M.
    Miron, C.
    Sorensen, S. L.
    de Brito, A. N.
    Bjorneholm, O.
    Karlsson, L.
    Svensson, S.
    Geometrical information on core-excited states obtained from interference quenching of vibrational states in resonant x-ray photoemission2003In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 67, no 2Article in journal (Refereed)
    Abstract [en]

    An interference quenching of the m=1 final state vibrational line in the resonant Auger decay of N 1s-->pi(*) core-excited N-2 is observed and analyzed. The intensity ratio between the m=1 and m=0 vibrational levels of the X (2)Sigma(g)(+) final state shows a surprising nonmonotonic variation as a function of frequency detuning, going through a minimum with a complete suppression of m=1. We have developed a simple model which indicates a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance of the core-excited state. This implies the possibility of determining the equilibrium bond distances for core-excited states to a high degree of accuracy. Simultaneously with the simple model we present a strict theory of the studied effect. This strict theory allows us to explore the accuracy of determining the bond length of the core-excited state from resonant Auger spectra. We obtain a weak influence of the core-hole lifetime on the determined bond length, whereas the number of intermediate vibrational states accounted for in the numerical simulations seems to be quite important.

  • 9. Baev, A.
    et al.
    Gelmukhanov, Faris
    KTH, Superseded Departments (pre-2005), Chemistry.
    Kimberg, Viktor
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Nonlinear propagation of strong multi-mode fields2003In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 36, p. 3761-3774Article in journal (Refereed)
    Abstract [en]

    We develop a strict theory of nonlinear propagation of few interacting stronglight beams. The key idea of our approach is a self-consistent solution ofthe nonlinear wave equation and the density matrix equations of the materialbeyond the rotatory wave approximation. We assume a Fourier expansion ofthe density matrixwhich goes beyond the conventionalTaylor expansions of thepolarization over the field amplitudeswhich is inadequate for the field strengthsthat we are interested in. Two qualitatively different situations are considered,with and without phase matching. Unlike in our previous paper (Baev et al2003 J. Opt. Soc. Am. B at press) devoted to the three-photon (TP) absorptioninduced upconverted lasing, we obtain here a strict solution for the nonlinearinteraction between different light beams. The general theory is applied to anumerical study of the role of saturation in TP photoabsorption by an organicchromophore in solution.

  • 10. Baev, A.
    et al.
    Gel'mukhanov, Faris
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Macak, P.
    Luo, Yi
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments (pre-2005), Biotechnology.
    General theory for pulse propagation in two-photon active media2002In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 117, no 13, p. 6214-6220Article in journal (Refereed)
    Abstract [en]

    The propagation of laser pulses of different lengths in nonlinear media of organic absorbers is described starting out from a recently suggested dynamical theory for two-photon absorption (TPA) of molecules in solutions [J. Opt. Soc. Am. B 19, 937 (2002)]. The roles of saturation effects and pulse duration on the suppression of TPA are emphasized. The numerical simulations of the pulse propagation are performed for a two-photon active charge transfer molecule using molecular parameters obtained from first principle calculations.

  • 11. Baev, A.
    et al.
    Gel'mukhanov, Faris
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Salek, Pawel
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Ueda, K.
    de Fanis, A.
    Okada, K.
    Sorensen, S.
    Doppler interference in dissociative resonant photoemission2002In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 66, no 2Article in journal (Refereed)
    Abstract [en]

    Resonant photoemission involving dissociative core excited states has been the subject of a great number of experimental and theoretical investigations in recent time. The resonant decay of such dissociating systems has been shown to lead to semiatomic Auger electron emission spectra, with particular angular behavior. In the present paper a detailed theoretical analysis of dissociative resonant photoemission spectra of homonuclear diatomic molecules is presented. The theory addresses both fixed in space and randomly oriented homonuclear molecules and emphasizes the Doppler effect and the role of the interference between channels referring to the Doppler split atomic fragments. It is shown that peaks originating from decay in the atomic fragments can be asymmetric and structured due to the Doppler interference effect. The predicted strong non-Lorentzian behavior of the substructure on the top of the Doppler broadened atomiclike contribution is traced to the interplay between decay channels leading to gerade and ungerade final states. Simulations based on wave-packet theory are compared with experimental data for molecular oxygen. Our numerical simulations of the atomiclike resonance of fixed in space molecules show that the spectral profile is very sensitive to the shape of interatomic potentials of core excited and final states. It is shown that the Doppler effect in the decay spectra depends upon the symmetry of the core excited state.

  • 12. Baev, A.
    et al.
    Kimberg, Viktor
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Polyutov, Sergey
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Gelmukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Bi-directional description of amplified spontaneous emission induced by three-photon absorption2005In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 22, no 2, p. 385-393Article in journal (Refereed)
    Abstract [en]

     A semiclassical dynamic theory of the nonlinear propagation of a few interacting intense light pulses is applied to study the nonlinear counterpropagation of amplified spontaneous emission (ASE) induced by three-photon absorption of short intense laser pulses in a chromophore solution. Several important results from the modeling are reached for the ASE process developing in the regime of strong saturation. Accounting for ASE in both forward and backward directions with respect to the pump pulse results in a smaller efficiency of nonlinear conversion for the forward ASE compared with the case in which forward emission is considered alone, something that results from the partial repump of the absorbed energy to the backward ASE component; the overall efficiency is nevertheless higher than for the forward emission considered alone. The efficiency of nonlinear conversion of the pump energy to the counterpropagating ASE pulses is strongly dependent on the concentration of active molecules so that a particular combination of concentration versus cell length optimizes the conversion coefficient. Under certain specified conditions, the ASE effect is found to be oscillatory; the origin of oscillations is dynamical competition between stimulated emission and off-resonant absorption. This result can be considered one of the possible explanations of the temporal fluctuations of the forward ASE pulse [Nature 415, 767 (2002)].

  • 13. Baev, A.
    et al.
    Salek, Pawel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Quantum-classical modeling of nonlinear pulse propagation in a dissolved two-photon active chromophore2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 11, p. 5379-5385Article in journal (Refereed)
    Abstract [en]

    In the present work we outline the implications of a quantum-classical approach for modeling two-photon absorption of organic chromophores in solution. The approach joins many-photon absorption dynamic simulations with quantum chemical first principles calculations of corresponding excitation energies and transition matrix elements. Among a number of conclusions of the study, we highlight three: (i) The use of either short- or long-pulse excitation is demonstrated to switch the absorptive capacity of the nonlinear medium owing to enhancement of the nonlinear stepwise processes; (ii) The two-photon cross section strongly depends on the way in which the dephasing rate decays when the laser frequency is tuned off-resonant with the corresponding molecular transition; (iii) The results of the pulse propagation simulations based on electronic structure data obtained with a new Coulomb attenuated functional is shown to be in much better agreement with the experimental results than those based on data received with traditional density functionals.

  • 14. Baev, A
    et al.
    Salek, Pawel
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Gelmukhanov, Faris
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments (pre-2005), Biotechnology.
    de Brito, N
    Bjorneholm, O
    Svensson, S
    Picturing molecular femtosecond processes through an ultra-fast controllable X-ray shutter2003In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 289, no 1, p. 51-56Article in journal (Refereed)
    Abstract [en]

    We show that frequency detuning in a resonant X-ray scattering experiment acts as an X-ray camera shutter by regulating the duration time of the scattering process. The camera shutter can be used to select processes at different time scales for observation. This is illustrated by a resonant Auger study of the ultra-fast dissociation of the core-excited HF molecule. We present experimental results and first principle simulations of the molecular fraction in the resonant Auger spectra of HF which is a dynamical parameter that well illustrates X-ray shutter controlled dissociation.

  • 15. Baev, A.
    et al.
    Welinder, P.
    Erlandsson, R.
    Henriksson, J.
    Norman, P.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    A quantum mechanical - Electrodynamical approach to nonlinear properties: Application to optical power limiting with platinum-organic compounds2007In: Journal of nonlinear optical physics and materials, ISSN 0218-8635, Vol. 16, no 2, p. 157-169Article in journal (Refereed)
    Abstract [en]

    Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper the results of systematic studies of this problem for isotropic media. Our theoretical approach - the quantum mechanical-electrodynamical (QMED) approach - is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell's equations. This allows us to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation enables us to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime, it is often necessary to simultaneously account for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is highlighted here in a study of the optical power limiting with platinum-organic molecular compounds. © World Scientific Publishing Company.

  • 16. Baev, A.
    et al.
    Welinder, P.
    Erlandsson, R.
    Henriksson, J.
    Norman, P.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Light-matter interaction of strong laser pulses in the micro-, nano-, and picosecond regimes2007In: Materials Research Society Symposium Proceedings, 2007, p. 12-29Conference paper (Refereed)
    Abstract [en]

    Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper results of systematic studies of this problem for isotropic media. Our theoretical approach-the quantum mechanical-electrodynamical (QMED) approach-is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell s equations. This allows to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation allows to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime it is often necessary to account simultaneously for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is here highlighted in a study of the optical power limiting with platinum-organic molecular compounds. © 2007 Materials Research Society.

  • 17.
    Baev, Alexander
    et al.
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Gel'mukhanov, Faris
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Rubio-Pons, Oscar
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Cronstrand, Peter
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Upconverted lasing based on many-photon absorption: an all dynamic description2004In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 21, no 2, p. 384-396Article in journal (Refereed)
    Abstract [en]

    A theory is developed for the propagation through a nonlinear medium of strong pump and amplifiedspontaneous-emission pulses. The theory is based on a solution of the density matrix equations that aims at providing an adequate treatment of the nonlinear polarization of the material without addressing the Taylor expansion over the powers of intensity. The theory has been applied for modeling of three-photon absorption induced upconverted stimulated emission of organic molecules in solvents. Numerical results are presented for the organic chromophore 4-[N-(2-hydroxyethyl)-N-(methyl)amino phenyl]-4'-(6-hydroxyhexyl sulfonyl) stilbene dissolved in dimethyl sulfoxide. The results are in good agreement with available experimental results.

  • 18. Baev, Alexander
    et al.
    Norman, Patrick
    Henriksson, Johan
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Theoretical Simulations of clamping levels in optical power limiting2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 42, p. 20912-20916Article in journal (Refereed)
    Abstract [en]

    Multiphysics modeling, combining quantum mechanical and classical wave mechanical theories, of clamping levels has been performed for a platinum(II) organic compound in a sol-gel glass matrix. A clamping level of 2.5 mu J is found for a pulse duration of 10 ns. The excited-state absorption in the triplet manifold is shown to be crucial for clamping to occur.

  • 19. Baev, Alexander
    et al.
    Prasad, Paras N.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Samoc, Marek
    Wegener, Martin
    Metaphotonics: An emerging field with opportunities and challenges2015In: Physics reports, ISSN 0370-1573, E-ISSN 1873-6270, Vol. 594, p. 1-60Article, review/survey (Refereed)
    Abstract [en]

    Metaphotonics is an emerging multidisciplinary field that deals with manipulation of electro-magnetic fields in nanoengineered (meta)materials using both electric and magnetic interactions and their cross-coupling. It offers unprecedented control of both linear and nonlinear optical functions for applications ranging from optical switching, to negative- and near-zero refractive index metamaterials, to chiral bioimaging, to cloaking. However, realization of such applications requires physics-guided nanoengineering of appropriate artificial media with electro-magnetic properties at visible and infrared wavelengths that are tailored to surpass those of any naturally-occurring material. Here, we review metaphotonics with a broadened vision and scope, introduce potential applications, describe the role of theoretical physics through multiscale modeling, review the materials development and current status, and outline opportunities in this fertile emerging field.

  • 20.
    Baev, Alexander
    et al.
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Rubio-Pons, Oscar
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Gel'Mukhanov, Faris
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Optical limiting properties of Zinc- and Platinum-based organometallic compounds2004In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 108, no 36, p. 7406-7416Article in journal (Refereed)
    Abstract [en]

    Optical power limiting is theoretically studied using an approach that combines quantum electronic structure calculations of multiphoton excitations and classical calculations of dynamical wave propagation. We illustrate the capability of such a combined approach by presenting results for a couple of organometallic compounds; basic metal-base porphyrins, vinylphenylamine porhyrin, and the so-called type IVc platinum compound. A comparative analysis of their electronic properties related to nonlinear absorption of electromagnetic radiation and their optical limiting capability has been performed based on dynamical simulations of the nonlinear pulse propagation taking account of resonant as well as off-resonant effects. Several key features and rate-limiting steps in the transmission have been examined in relation to various characteristics of the pulse. It is found that the resonant vs off-resonant conditions, the saturation conditions and the dephasing play critical roles for the nonlinear transmission. The saturation effects are sensitive to the pulse duration, the inter-system crossing rate and the quenching of the higher triplet state. The inter-system crossing rate has to be comparable with the inverse pulse duration in order to boost the stepwise two-photon channel associated with singlet-singlet followed by triplet-triplet transitions. It is illustrated that structure-to-property relations of the rate-limiting steps serve as important criteria for choices of compounds suitable for the application of interest.

  • 21.
    Bagheri, Niusha
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics. Photonics Laboratory, Physics Department, Kharazmi University, Tehran, Iran.
    Liu, Qingyun
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Bergstrand, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Pu, R.
    Centre for Optical and Electromagnetic Research, Guangdong Provincial Key Laboratory of Optical Information.
    Zhan, Q.
    Centre for Optical and Electromagnetic Research, Guangdong Provincial Key Laboratory of Optical Information.
    Ara, M. H. M.
    Photonics Laboratory, Physics Department, Kharazmi University, Tehran, Iran.
    Ågren, Hans
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Liu, Haichun
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Widengren, Jerker
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Change in the emission saturation and kinetics of upconversion nanoparticles under different light irradiations2019In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 97, article id 109389Article in journal (Refereed)
    Abstract [en]

    Nd3+-sensitized upconversion nanoparticles (UCNPs) can be excited by both 980 and 808 nm light, which is regarded as a particularly advantageous property of these particles. In this work, we demonstrate that the nanoparticles can exhibit significantly different response when excited at these two excitation wavelengths, showing dependence on the intensity of the excitation light and the way it is distributed in time. Specifically, with 808 nm excitation saturation in the emitted luminescence is more readily reached with increasing excitation intensities than upon 980 nm excitation. This is accompanied by delayed upconversion luminescence (UCL) kinetics and weaker UCL intensities. The different luminescence response at 808 and 980 nm excitation reported in this work is relevant in a manifold of applications using UCNPs as labels and sensors. This could also open new possibilities for multi-wavelength excitable UCNPs for upconversion color display and in laser-scanning microscopy providing selective readouts and sub-sectioning of samples.

  • 22. Bai, Linyi
    et al.
    Zhu, Liangliang
    Ang, Chung Yen
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wu, Shaojue
    Zeng, Yongfei
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhao, Yanli
    Iron( III)-Quantity-Dependent Aggregation-Dispersion Conversion of Functionalized Gold Nanoparticles2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 14, p. 4032-4037Article in journal (Refereed)
    Abstract [en]

    Developing gold nanoparticles (AuNPs) with well-designed functionality is highly desirable for boosting the performance and versatility of inorganic-organic hybrid materials. In an attempt to achieve ion recognition with specific signal expressions, we present here 4-piperazinyl-1,8-naphthalimide-functionalized AuNPs for the realization of quantitative recognition of Fe-III ions with dual (colorimetric and fluorescent) output. The research takes advantage of 1)quantity-controlled chelation-mode transformation of the piperazinyl moiety on the AuNPs towards Fe-III, thereby resulting in an aggregation-dispersion conversion of the AuNPs in solution, and 2)photoinduced electron transfer of a naphthaimide fluorophore on the AuNPs, thus leading to reversible absorption and emission changes. The functional AuNPs are also responsive to pH variations. This strategy for realizing the aggregation-dispersion conversion of AuNPs with returnable signal output might exhibit application potential for advanced nanoscale chemosensors.

  • 23.
    Balamurugan, Kanagasabai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Natarajan Arul, Murugan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Langström, Bengt
    Nordberg, Agneta
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Siberian Federal University, Russian Federation.
    Effect of Alzheimer Familial Chromosomal Mutations on the Amyloid Fibril Interaction with Different PET Tracers: Insight from Molecular Modeling Studies2017In: ACS Chemical Neuroscience, E-ISSN 1948-7193, Vol. 8, no 12, p. 2655-2666Article in journal (Refereed)
    Abstract [en]

    Alzheimer's disease (AD) is the most common neurodegenerative disorder. Along with an increasing number of elderly worldwide, it poses a great challenge for the society and health care. Although sporadic AD is the common form of AD, 2-3% of the AD cases are expected to be due to mutations in the fi region of the amyloid precursor protein, which is referred to as autosomal dominant AD (ADAD). These mutations may cause changes in the secondary structure of the amyloid fi fibrils and may alter the fibrillization rate leading to changes in the disease development and could also affect the binding to tracers used in diagnosis. In particular, from some recent clinical studies using PET tracers for detection of fibrillar amyloids, it is evident that in ADAD patients with Arctic mutation no amyloid plaque binding can be detected with the "C Pittsburgh Compound B (C-11-PIB). However, for in vitro conditions, significant binding of H-3-PIB has been reported for the amyloid fibrils carrying the Arctic mutation. The aim of the present study is to investigate if there is any mutation specific binding of commonly used amyloid tracers, namely, florbetaben, florbetapir, FPIB, AZD4694, and AZD2184, by means of molecular modeling techniques. Other than Arctic, ADAD mutations, such as the Dutch, Italian, Iowa, and Flemish mutations, are considered in this study. We report that all tracers except florbetapir show reduced binding affinity toward amyloid beta fibrils with the Arctic mutation when compared to the native type. Moreover, florbetapir is the only tracer that binds to all mutants with increased affinity when compared to the native fibril. The results obtained from these studies could increase the understanding of the structural changes caused by mutation and concomitant changes in the interaction pattern of the PET tracers with the mutated variants, which in turn can be useful in selecting the appropriate tracers for the purpose of diagnosis as well as for designing new tracers with desirable properties.

  • 24.
    Balamurugan, Kanagasabai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Natarajan Arul, Murugan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry. KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Multistep Modeling Strategy To Improve the Binding Affinity Prediction of PET Tracers to A beta(42): Case Study with Styrylbenzoxazole Derivatives2016In: ACS CHEMICAL NEUROSCIENCE, ISSN 1948-7193, Vol. 7, no 12, p. 1698-1705Article in journal (Refereed)
    Abstract [en]

    Positron emission tomography (PET) tracers play an important role in the diagnosis of Alzheimer's disease, a condition that leads to progressive dementia and memory loss. A high binding affinity and specificity of the PET tracers to amyloid oligomers and fibrils are crucial for their successful application as diagnostic agents. In this sense, it is essential to design PET tracers with enhanced binding affinities, which can lead to more precise and earlier detection of Alzheimer's disease conditions. The application of in silico methodology for the design and development of efficient PET tracers may serve as an important route to improved Alzheimer's disease diagnosis. In this work, the performance of widely used computational methods is explored for predicting experimental binding affinities of styrylbenzoxazole (SB) derivatives against a common amyloid protofibril. By performing docking, molecular dynamics, and quantum chemistry calculations in sequence their combined predictive performance is explored. The present work emphasizes the merits as well as limitations of these simulation strategies in the realm of designing PET tracers for Alzheimer's disease diagnosis.

  • 25.
    Banerjee, Saikat
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Abergel, David
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Ågren, Hans
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Aeppli, G.
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland.;Swiss Fed Inst Technol, Lab Solid State Phys, CH-8093 Zurich, Switzerland.;EPF Lausanne, Inst Phys, CH-1015 Lausanne, Switzerland..
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Interacting Dirac materials2020In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 32, no 40, article id 405603Article in journal (Refereed)
    Abstract [en]

    We investigate the extent to which the class of Dirac materials in two-dimensions provides general statements about the behavior of both fermionic and bosonic Dirac quasiparticles in the interacting regime. For both quasiparticle types, we find common features for the interaction induced renormalization of the conical Dirac spectrum. We perform the perturbative renormalization analysis and compute the self-energy for both quasiparticle types with different interactions and collate previous results from the literature whenever necessary. Guided by the systematic presentation of our results in table1, we conclude that long-range interactions generically lead to an increase of the slope of the single-particle Dirac cone, whereas short-range interactions lead to a decrease. The quasiparticle statistics does not qualitatively impact the self-energy correction for long-range repulsion but does affect the behavior of short-range coupled systems, giving rise to different thermal power-law contributions. The possibility of a universal description of the Dirac materials based on these features is also mentioned.

  • 26.
    Banerjee, Saikat
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Institute for Materials Science, Los Alamos National Laboratory, USA.
    Fransson, J.
    Black-Schaffer, A. M.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Balatsky, A. V.
    Granular superconductor in a honeycomb lattice as a realization of bosonic Dirac material2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 13, article id 134502Article in journal (Refereed)
    Abstract [en]

    We examine the low-energy effective theory of phase oscillations in a two-dimensional granular superconducting sheet where the grains are arranged in a honeycomb lattice structure. Using the example of graphene, we present evidence for the engineered Dirac nodes in the bosonic excitations: the spectra of the collective bosonic modes cross at the K and K' points in the Brillouin zone and form Dirac nodes. We show how two different types of collective phase oscillations are obtained and that they are analogous to the Leggett and the Bogoliubov-Anderson-Gorkov modes in a two-band superconductor. We show that the Dirac node is preserved in the presence of an intergrain interaction, despite induced changes of the qualitative features of the two collective modes. Finally, breaking the sublattice symmetry by choosing different on-site potentials for the two sublattices leads to a gap opening near the Dirac node, in analogy with fermionic Dirac materials. The Dirac node dispersion of bosonic excitations is thus expanding the discussion of the conventional Dirac cone excitations to the case of bosons. We call this case as a representative of bosonic Dirac materials (BDM), similar to the case of Fermionic Dirac materials extensively discussed in the literature.

  • 27.
    Banerjee, Saikat
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Los Alamos Natl Lab, USA.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Landau-like states in neutral particles2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 23, article id 235134Article in journal (Refereed)
    Abstract [en]

    We show the emergence of a new type of dispersion relation for neutral atoms with an interesting similarity to the spectrum of two-dimensional electrons in an applied perpendicular constant magnetic field. These neutral atoms can be confined in toroidal optical traps and give quasi-Landau spectra. In strong contrast to the equidistant infinitely degenerate Landau levels for charged particles, the spectral gap for such two-dimensional neutral particles increases in particular electric-field configurations. The idea in the paper is motivated by the development in cold atom experiments and builds on the seminal paper of Aharonov and Casher.

  • 28. Baryshnikov, G. V.
    et al.
    Minaev, B. F.
    Minaeva, V. A.
    Podgornaya, A. T.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Application of Bader's atoms in molecules theory to the description of coordination bonds in the complex compounds of Ca2+ and Mg2+ with methylidene rhodanine and its anion2012In: Russian journal of general chemistry, ISSN 1070-3632, E-ISSN 1608-3350, Vol. 82, no 7, p. 1254-1262Article in journal (Refereed)
    Abstract [en]

    In the framework of Bader's atoms in molecules theory a complete analysis of the distribution function of electron density in molecules of complexes of Ca2+ and Mg2+ with methylidene rhodanine and its anion was carried out. The role of mutual polarization of the metal cation and the ligand in the formation of coordination bonds was demonstrated. The accumulation of electron density in the interatomic space of coordination bonds is assumed to be a consequence of the deformation of the ligand electron shell under the influence of the cation electric field. Based on the magnitude and sign of the Laplacian and the electron energy density at the critical points of coordination bonds the interactions were classified the in terms of the atoms in molecules theory. The energy of the coordination bonds was evaluated using the Espinoza's formula. The stability of metal-containing rings was considered basing on the values of the bond ellipticity.

  • 29. Baryshnikov, G. V.
    et al.
    Minaev, B. F.
    Minaeva, V. A.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Theoretical study of the conformational structure and thermodynamic properties of 5-(4-oxo-1,3-thiazolidine-2-ylidene)-rhodanine and ethyl-5-(4-oxo-1,3-thiazolidine-2-ylidene)-rhodanine-3-acetic acid as acceptor groups of indoline dyes2010In: Journal of Structural Chemistry, ISSN 0022-4766, E-ISSN 1573-8779, Vol. 51, no 5, p. 817-823Article in journal (Refereed)
    Abstract [en]

    The quantum chemical DFT method with the B3LYP hybrid functional in 6-31++G(d,p) and 6-311+G(d,p) basis sets is used to calculate the equilibrium geometric parameters of different conformations of 5-(4-oxo-1,3-thiazolidine-2-ylidene)-rhodanine and its substituted form ethyl-5-(4-oxo-1,3-thiazolidine-2-ylidene)-rhodanine-3'-acetic acid applied in the synthesis of indoline and some other sensitizing dyes for solar cells. The thermodynamic parameters of four conformers and their synthesis reactions are calculated. The effect of substituents on the thermodynamic stability of the studied isomers is shown.

  • 30.
    Baryshnikov, Gleb
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Bohdan Khmelnytsky National University, Ukraine.
    Minaev, Boris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Bohdan Khmelnytsky National University, Ukraine.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Siberian Federal University, Russia.
    Theory and Calculation of the Phosphorescence Phenomenon2017In: Chemical Reviews, ISSN 0009-2665, E-ISSN 1520-6890, Vol. 117, no 9, p. 6500-6537Article, review/survey (Refereed)
    Abstract [en]

    Phosphorescence is a phenomenon of delayed luminescence that corresponds to the radiative decay of the molecular triplet state. As a general property of molecules, phosphorescence represents a cornerstone problem of chemical physics due to the spin prohibition of the underlying triplet-singlet emission and because its analysis embraces a deep knowledge of electronic molecular structure. Phosphorescence is the simplest physical process which provides an example of spin-forbidden transformation with a characteristic spin selectivity and magnetic field dependence, being the model also for more complicated chemical reactions and for spin catalysis applications. The bridging of the spin prohibition in phosphorescence is commonly analyzed by perturbation theory, which considers the intensity borrowing from spin-allowed electronic transitions. In this review, we highlight the basic theoretical principles and computational aspects for the estimation of various phosphorescence parameters, like intensity, radiative rate constant, lifetime, polarization, zero-field splitting, and spin sublevel population. Qualitative aspects of the phosphorescence phenomenon are discussed in terms of concepts like structure-activity relationships, donor-acceptor interactions, vibronic activity, and the role of spin-orbit coupling under charge-transfer perturbations. We illustrate the theory and principles of computational phosphorescence by highlighting studies of classical examples like molecular nitrogen and oxygen, benzene, naphthalene and their azaderivatives, porphyrins, as well as by reviewing current research on systems like electrophosphorescent transition metal complexes, nucleobases, and amino acids. We furthermore discuss modern studies of phosphorescence that cover topics of applied relevance, like the design of novel photofunctional materials for organic light-emitting diodes (OLEDs), photovoltaic cells, chemical sensors, and bioimaging.

  • 31.
    Baryshnikov, Gleb V.
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. Tomsk State Univ, 36 Lenin Ave, Tomsk, Russia..
    Sunchugashev, Dmitry A.
    Tomsk State Univ, 36 Lenin Ave, Tomsk, Russia..
    Valiev, Rashid R.
    Tomsk State Univ, 36 Lenin Ave, Tomsk, Russia..
    Minaev, Boris F.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Vibronic absorption spectra of the angular fused bisindolo- and biscarbazoloanthracene blue fluorophores for OLED applications2018In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 513, p. 105-111Article in journal (Refereed)
    Abstract [en]

    An in-depth analysis of the vibronic absorption spectra for the recently synthesized blue-fluorescent OLED emitters bis[(1,2)(5,6)]indoloanthracene and biscarbazolo[3,4-a:3',4'-h]anthracene has been carried out computationally at the density functional theory level within the Franck-Condon approximation. These molecules are characterized by extended and rich electronic absorption spectra with most absorption bands being of vibronic origin. The first excited singlet state of bis[(1,2)(5,6)]indoloanthracene compound demonstrates a clear observable double-peak vibronic progression for two different active modes in the absorption spectrum, while the S-2 state is vibronically inactive. In contrast, for the larger biscarbazolo[3,4-a:3',4'-h]anthracene compound the S-0 -> S-2 transition demonstrates well-resolved intense vibronic bands which overlap the less intense progressions of few modes in the S-0 -> S-1 transition. We have also found, that even the higher-lying and very intense S-0 -> S-4 and S-0 -> S-5 transitions for bis[(1,2)(5,6)]indoloanthracene and biscarbazolo[3,4-a:3',4'-h]anthracene, respectively, are characterized by clear vibronic progressions in excellent agreement with experimental spectra.

  • 32.
    Baryshnikov, Gleb V.
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Valiev, R. R.
    Natl Res Tomsk Polytech Univ, Res Sch Chem & Appl Biomed Sci, Lenin Ave 30, Tomsk 634050, Russia.;Univ Helsinki, Dept Chem, FIN-00014 Helsinki, Finland..
    Cherepanov, V. N.
    Tomsk State Univ, 36 Lenin Ave, Tomsk, Russia..
    Karaush-Karmazin, N. N.
    Bohdan Khmelnytsky Natl Univ, Dept Chem & Nanomat Sci, UA-18031 Cherkassy, Ukraine..
    Minaeva, V. A.
    Bohdan Khmelnytsky Natl Univ, Dept Chem & Nanomat Sci, UA-18031 Cherkassy, Ukraine..
    Minaev, B. F.
    Bohdan Khmelnytsky Natl Univ, Dept Chem & Nanomat Sci, UA-18031 Cherkassy, Ukraine..
    Ågren, Hans
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Aromaticity and photophysics of tetrasila- and tetragerma-annelated tetrathienylenes as new representatives of the hetero[8]circulene family2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 18, p. 9246-9254Article in journal (Refereed)
    Abstract [en]

    The electronic structure, absorption and emission spectra, aromaticity and photophysical behavior of the recently synthesized tetrasilatetrathia[8]circulene and tetragermatetrathia[8]circulene compounds have been studied computationally. Both compounds demonstrate a specific bifacial aromaticity, which is unusual for hetero[8]circulenes; the inner eight-membered core sustains an expected strong paratropic magnetically-induced ring current, while the outer perimeter contains saturated Si(Et)(2) and Ge(Et)(2) moieties which break the conjugation between the thiophene rings. The overall magnetically-induced ring current for both studied circulenes is close to zero because of the strong local diatropic currents in each thiophene ring that compensate the paratropic counterpart. The electronic absorption and emission spectra of tetrasilatetrathia[8]circulene and tetragermatetrathia[8]circulene demonstrate a clear visible vibronic progression. The 0-0 band is the most active one in the absorption spectra, while in the fluorescence spectra the 0-1 band composed of several normal vibrations is more intense compared with the 0-0 band in excellent agreement with experiment. Accounting for spin-orbit coupling effects, an analysis of the photophysical constants for the two compounds demonstrates: (1) a clear manifestation of the internal heavy atom effect on the inter-system crossing efficiency; (2) one to two order domination of non-radiative rates over the fluorescence rate; and (3) that the S-1-S-0 internal conversion is extremely slow and can not compete with the fluorescence, while the S-1-T-n inter-system crossing is a main deactivation channel of the S-1 excited state. These results provide new insight into the electronic structure and photophysics of tetrasilatetrathia[8]circulene and tetragermatetrathia[8]circulene as novel standalone representatives of hetero[8]circulenes - tetraannelated derivatives of tetrathienylene.

  • 33.
    Baryshnikov, Gleb V.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Bogdan Khmelnitsky Natl Univ.
    Valiev, Rashid R.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Tomsk State Univ; Tomsk Polytech Univ.
    Karaush, Nataliya N.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Minaeva, Valentina A.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sinelnikov, Alexandr N.
    Pedersen, Stephan K.
    Pittelkow, Michael
    Minaev, Boris F.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Benzoannelated aza-, oxa- and azaoxa[8]circulenes as promising blue organic emitters2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 40, p. 28040-28051Article in journal (Refereed)
    Abstract [en]

    In the present work, we studied the synergetic effect of benzoannelation and NH/O-substitution for enhancing the absorption intensity in a series of novel designed benzoannelated aza- and oxa[8]circulenes. Semi-empirical estimations of the fluorescence rate constants allowed us to determine the most promising fluorophores among all the possible benzoannelated aza-, oxa- and mixed azaoza[8]circulenes. Among them, para-dibenzoannelated [8]circulenes demonstrated the most intense light absorption and emission due to the prevailing role of the linear acene chromophore. Calculated phi(fl) values are in complete agreement with experimental data for a number of already synthesized circulenes. Thus, we believe that the most promising circulenes designed in this study can demonstrate an intensive fluorescence in the case of their successful synthesis, which in turn could be extremely useful for the fabrication of future blue OLEDs. Special attention is devoted to the aromaticity features and peculiarities of the absorption spectra for the two highly-symmetrical (D-4h ground state symmetry) pi-isoelectronic species as well as the so-called tetrabenzotetraaza[8]circulene and tetrabenzotetraoxa[8]circulene molecules. Both of them are characterized by rich electronic spectra, which can be assigned only by taking into account the vibronic coarse structure of the first electronic absorption band; the 0-1 and 0-2 transitions were found to be active in the absorption spectrum in complete agreement with experimental data obtained for both energy and intensity. The corresponding promotive vibrational modes have been determined and their vibronic activity estimated using the Franck-Condon approximation.

  • 34.
    Baryshnikov, Gleb V.
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. Bohdan Khmelnytsky Natl Univ, Dept Chem & Nanomat Sci, UA-18031 Cherkassy, Ukraine.
    Valiev, Rashid R.
    Natl Res Tomsk Polytech Univ, Res Sch Chem & Appl Biomed Sci, Lenin Ave 30, Tomsk 634050, Russia.;Univ Helsinki, Fac Sci, Dept Chem, FIN-00014 Helsinki, Finland..
    Kuklin, Artem V.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. Siberian Fed Univ, Div Theoret Phys & Wave Phenomena, 79 Svobodniy Av, Krasnoyarsk 660041, Russia.
    Sundholm, Dage
    Univ Helsinki, Fac Sci, Dept Chem, FIN-00014 Helsinki, Finland..
    Ågren, Hans
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. Henan Univ, Coll Chem & Chem Engn, Kaifeng 475004, Henan, Peoples R China.
    Cyclo[18]carbon: Insight into Electronic Structure, Aromaticity, and Surface Coupling2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 21, p. 6701-6705Article in journal (Refereed)
    Abstract [en]

    Cyclo[18]carbon (C-18) is studied computationally at the density functional theory (DFT) and ab initio levels to obtain insight into its electronic structure, aromaticity, and adsorption properties on a NaCl surface. DFT functionals with a small amount of Hartree-Fock exchange fail to determine the experimentally observed polyyne molecular structure, revealing a cumulene-type geometry. Exchange-correlation functionals with a large amount of Hartree-Fock exchange as well as ab initio CASSCF calculations yield the polyyne structure as the ground state and the cumulene structure as a transition state between the two inverted polyyne structures through a Kekule distortion. The polyyne and the cumulene structures are found to be doubly Huckel aromatic. The calculated adsorption energy of cyclo[18]carbon on the NaCl surface is small (37 meV/C) and almost the same for both structures, implying that the surface does not stabilize a particular geometry.

  • 35.
    Baryshnikov, Gleb V.
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Valiev, Rashid R.
    Natl Res Tomsk Polytech Univ, Res Sch Chem & Appl Biomed Sci, Lenin Ave 30, Tomsk 634050, Russia.;Univ Helsinki, Dept Chem, FIN-00014 Helsinki, Finland..
    Li, Qizhao
    East China Univ Sci & Technol, Sch Chem & Mol Engn, Key Lab Adv Mat & Joint Int Res Lab Precis Chem &, Shanghai 200237, Peoples R China..
    Li, Chengjie
    East China Univ Sci & Technol, Sch Chem & Mol Engn, Key Lab Adv Mat & Joint Int Res Lab Precis Chem &, Shanghai 200237, Peoples R China..
    Xie, Yongshu
    East China Univ Sci & Technol, Sch Chem & Mol Engn, Key Lab Adv Mat & Joint Int Res Lab Precis Chem &, Shanghai 200237, Peoples R China..
    Ågren, Hans
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Computational study of aromaticity, H-1 NMR spectra and intermolecular interactions of twisted thia-norhexaphyrin and its multiply annulated polypyrrolic derivatives2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 45, p. 25334-25343Article in journal (Refereed)
    Abstract [en]

    The recently synthesized twisted thia-norhexaphyrin and its multiply annulated polypyrrolic derivatives have been studied computationally. Gauge-including magnetically induced current calculations predict a global nonaromatic character of the initial thia-norhexaphyrin due to the highly-twisted conformation of the macrocycle. Upon the oxidation of the thia-norhexaphyrin four multiply annulated polypyrrolic aromatic macrocycles are formed for which the global aromatic character is confirmed in agreement with experimentally measured H-1 NMR spectra. The calculation of the proton chemical shifts for the studied compounds by direct comparison with the tetramethylsilane standard leads to a significant mean absolute error. At the same time a linear regression procedure for the two selected groups of protons (CH and NH protons) provides much better values of calculated chemical shifts and tight correlation with experiment. The separate consideration of NH protons is motivated by the numerous intermolecular hydrogen bonds in which the protons are involved, which induce considerable upfield shifts, leading to a significant underestimation of the corresponding chemical shifts. Such a selected correlation can be used for accurate estimation of proton chemical shifts of the related porphyrinoids. Bader's theory of Atoms in Molecules has been applied for the studied twisted thia-norhexaphyrin and its multiply annulated polypyrrolic derivatives to characterize intramolecular H-bonds and other non-covalent interactions.

  • 36.
    Baryshnikov, Gleb V.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Bogdan Khmelnitsky National University, Ukraine; Tomsk State University, Russian Federation.
    Valiev, Rashid R.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Tomsk State University, Russian Federation; Tomsk Polytechnic University, Russian Federation.
    Minaev, Boris F.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Bogdan Khmelnitsky National University, Ukraine; Tomsk State University, Russian Federation.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    A computational study of aromaticity and photophysical properties of unsymmetrical azatrioxa[8]circulenes2017In: New Journal of Chemistry, ISSN 1144-0546, E-ISSN 1369-9261, Vol. 41, no 7, p. 2717-2723Article in journal (Refereed)
    Abstract [en]

    Owing to their potential use in organic light-emitting diodes and field-effect transistors we present a theoretical study of a series of unsymmetrical azatrioxa[8]circulenes in order to explain the impact of outer substituents and benzoannelation on photophysical constants and aromaticity of these compounds in terms of spin-orbit coupling perturbation and magnetically-induced ring currents. It is argued that the S1-Tn inter-system crossing processes constitute the main deactivation pathways for the fluorescence quenching, something that is supported by a good agreement obtained with experimental data on fluorescence quantum yields. The concept of the gauge-including magnetically induced currents has been applied in order to estimate the role of substituents and benzoannelated fragments on the aromaticity and particularly on the overall balance between the diatropic “aromatic” and paratropic “antiaromatic” current strengths. While a variation of the substituents in the outer perimeter of the studied circulenes does not provide a clear effect on their aromaticity, it is demonstrated that an additional benzoannelation (π-extension) of the azatrioxa[8]circulene macrocycle induces a significant aromaticity enhancement.

  • 37.
    Baryshnikov, Gleb V.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Tomsk State University, Russian Federation.
    Valiev, Rashid R.
    Minaev, Boris F.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Siberian Federal University, Russian Federation.
    Optical tuning of tetrabenzo[8]circulene derivatives through pseudorotational conformational isomerization2018In: Dyes and pigments, ISSN 0143-7208, E-ISSN 1873-3743, Vol. 151, p. 372-379Article in journal (Refereed)
    Abstract [en]

    In order to further search efficient [8]circulene materials for OLED applications we have theoretically investigated the structure and electronic, absorption spectra of functionalized tetrabenzo[8]circulenes with different substituents in the outer perimeter. These hydrocarbon materials complement the wide family of [8]circulenes which earlier have been demonstrated to possess promising emissive and exciplex-forming properties suitable for organic light emitting diodes. The hydrocarbon tetrabenzo[8]circulenes show saddle shape of the molecular skeleton which can exist in two different conformations with different curvatures of the macrocycle. The aromaticity, electronic structure and orbital pattern are found to be principally different for these two isomers, where the global minimum isomer is weakly antiaromatic and electronically less stable comparing with the non-aromatic local minimum structure. The absorption spectra are also very different: the global minimum structure is more active in the long-wavelength region while the local minimum isomer shows absorption only at short wavelengths. Our computational findings suggest a new concept for optical tuning of curved [8]circulenes through conformational isomerization and aromaticity control, thus through structural variations without changing the molecular composition. Based on this principle we have designed novel functionalized [8]circulenes with promising fluorescence activity.

  • 38.
    Baryshnikov, Gleb V.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Valiev, Rashid R.
    Minaev, Boris F.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Substituent-sensitive fluorescence of sequentially N-alkylated tetrabenzotetraaza[8]circulenes2017In: New Journal of Chemistry, ISSN 1144-0546, E-ISSN 1369-9261, Vol. 41, no 15, p. 7621-7625Article in journal (Refereed)
    Abstract [en]

    We explore the use of substituent-sensitive balance between fluorescence and non-radiative decay as a tool for optical tuning of promising materials for organic light emitting diode applications. A series of N-butylated tetrabenzotetraaza[8]circulenes is studied computationally in order to explain the gradual decrease of fluorescence intensity with the increase of the substituent number. The inter-system crossing probability is found to increase upon the gradual substitution of the circulene macrocycle as a result of the decrease of the S-1-T-1 energy gap due to the deformation of the tetrabenzotetraaza[8] circulenes and therefore the distortion of the pi-conjugation within the macrocycles. In contrast, the S-1-T-1 spin-orbit coupling matrix elements are quite insensitive to the number of outer substituents. As a result, the fluorescence-responsible pi pi(star) transition becomes less intense and the fluorescence rate constant decreases.

  • 39.
    Baryshnikov, Glib V.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Bogdan Khmelnitsky Cherkasy National University, Ukraine.
    Bondarchuk, S. V.
    Minaeva, V. A.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Minaev, Boris F.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Bogdan Khmelnitsky Cherkasy National University, Ukraine.
    Solvatochromic effect in absorption and emission spectra of star-shaped bipolar derivatives of 1,3,5-triazine and carbazole. A time-dependent density functional study2017In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 23, no 2, article id 55Article in journal (Refereed)
    Abstract [en]

    A series of three star-shaped compounds containing both donor (carbazole) and acceptor (2,4,6-triphenyl-1,3,5-triazine) moieties linked through various linking bridges was studied theoretically at the linear response TD-DFT level of theory to describe their absorption and fluorescence spectra. The concept of a localized charge-transfer excited state has been applied successfully to explain the observed strong solvatochromic effect in the emission spectra of the studied molecules, which can be utilized for the fabrication of color tunable solution-processable OLEDs. The concept is in particularly applicable to donor–acceptor species with a C3 symmetry point group where the static dipole moment changes dramatically upon electronic excitation. An important peculiarity of the studied molecules is that they are characterized by non-zero values of the HOMO and LUMO orbitals in the same common part of molecular space that provides a large electric dipole transition moment for both light absorption and emission. [Figure not available: see fulltext.]

  • 40.
    Baryshnikov, Glib V.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Cherkasy National University, Ukraine.
    Minaev, B. F.
    Baryshnikova, A. T.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Siberian Federal University, Russian Federation.
    A computational study of structural and magnetic properties of bi- and trinuclear Cu(II) complexes with extremely long Cu–-Cu distances2017In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 491, p. 48-55Article in journal (Refereed)
    Abstract [en]

    Three recently synthesized copper(II) complexes with aroylhydrazones of trifluoroacetic and benzenecarboxylic acids (Dalton Trans., 2013, 42, 16878) have been computationally investigated by density functional theory within the broken symmetry approximation accounting for empirical dispersion corrections. A topological analysis of electron density distributions has been carried out using Bader's “quantum theory of atoms in molecules” formalism. The calculated values of spin-spin exchange for the studied dinuclear complexes indicate a very weak ferromagnetic coupling of the unpaired electrons in good agreement with experimental data. At the same time, the trinuclear copper(II) complex possesses a low-spin doublet ground state with one ferromagnetic and two antiferromagnetic spin projections between the triangular-positioned Cu2+ ions. The estimated values of the coupling constants for the spin-spin exchange in this trinuclear complex are in a good agreement with experimental observations. The calculations support a mechanism of exchange coupling through the aromatic links in these strongly spin-separated systems.

  • 41.
    Baryshnikov, Glib V.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. V. D. Kuznetsov Siberian Physical-Technical Institute at National Research Tomsk State University, Russian Federation.
    Minaev, Boris F.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. V. D. Kuznetsov Siberian Physical-Technical Institute at National Research Tomsk State University, Russian Federation.
    Baryshnikova, A. A.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Anion-induced exchange interactions in binuclear complexes of Cu(II) with flexible hexadentate bispicolylamidrazone ligands2016In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 661, p. 48-52Article in journal (Refereed)
    Abstract [en]

    Two recently synthesized copper(II) complexes with spacer-armed bispicolylamidrazone ligands have been theoretically studied at the density functional theory (DFT) level accounting for empirical dispersion correction and intrinsic anionic environment by perchlorate ions. The exchange parameter between the open-shell singlet and triplet states of the studied complexes has been estimated by broken symmetry DFT calculations. The mechanism of spin-spin exchange interaction between the unpaired electrons via the σ-bond aliphatic chain (Gusev et al., 2015) is confirmed. Instead, a anion-induced mechanism is proposed which means that the anionic grid participates in the exchange interaction between the unpaired electrons.

  • 42. Baryshnikova, A. T.
    et al.
    Minaev, B. F.
    Baryshnikov, Gleb V.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Computational study of the structure and magnetic properties of the weakly-coupled tetranuclear square-planar complex of Cu(II) with a tetraporphyrin sheet2019In: Inorganica Chimica Acta, ISSN 0020-1693, E-ISSN 1873-3255, Vol. 485, p. 73-79Article in journal (Refereed)
    Abstract [en]

    Owing to the fact that weakly-coupled Cu(II) complexes are potentially applicable in the fields of spintronics and single-molecule magnets we have studied one particularly conspicuous case – a tetranuclear square-planar complex of Cu(II) ions with a π-extended tetraporphyrin ligand (Tetrahedron, 2008, 64, 11433), the structural criteria of which, with very long distances between the paramagnetic centers, can sensibly define the exchange coupling constants and magnetic behaviour. We use the “broken symmetry” density functional theory formalism for various spin states (open-shell singlet, triplet and quintet states). The calculated value of the magnetic exchange integral corresponds to a very weak antiferromagnetic coupling between the neighboring Cu(II) ions (Jcalc = –1.48 cm−1(calculated) Jexp = −1.16 cm−1 (experiment)). The opposite Cu(II) ions are coupled ferromagnetically with an extremely small exchange constant (jcalc = 0.09 cm−1 (calculated) that corresponds to the open-shell singlet ground state of the following spin configuration↑↓↑↓. The exchange mechanism between the [Cu(n) + 4N] localized singly-occupied “magnetic” orbitals of the dxy(Cu) + 4sp2(N) nature indicates a diffuse non-zero overlap between them on the Carbon atoms of the organic ligand. The numerical analysis of atomic spin densities and corresponding decomposition coefficients for the singly-occupied “magnetic” orbitals confirm the proposed exchange mechanism. This superexchange pathway is mediated by the in-plane sp2-hybrid orbitals of the Carbon atoms that couple four [Cu + 4N] fragments by the σ-bond system. For more detailed characterization of the target system a topological analysis of electron density distributions in the high-spin quintet states has been carried out using the Bader's method “quantum theory of atoms in molecules”.

  • 43. Bednarska, Joanna
    et al.
    Zalesny, Robert
    Murugan, N. Arul
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Bartkowiak, Wojciech
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Odelius, Michael
    Elucidating the Mechanism of Zn2+ Sensing by a Bipyridine Probe Based on Two-Photon Absorption2016In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, no 34, p. 9067-9075Article in journal (Refereed)
    Abstract [en]

    In this work, we examine, by means of computational methods, the mechanism of Zn2+ sensing by a bipyridine-centered, D-pi-A-pi-D-type-ratiometric molecular probe. According to recently published experimental data [Divya, K. P.; Sreejith, S.; Ashokkumar, P.; Yuzhan, K.; Peng, Q; Maji, S. K.; Tong, Y.; Yu, H.; Zhao, Y.; Ramamurthy, P.; Ajayaghosh, A. A ratiometric fluorescent molecular -probe with enhanced two-photon response upon Zn2+ binding for in vitro and in vivo: bioimaging.= Chem. Sci. 2014, S, 3469-3474], after coordination to zinc ions the -probe exhibits a large enhancement of the two -photon absorption cross section. The goal of our investigation was to elucidate the mechanism behind this phenomenon. For this purpose, linear and nonlinear optical properties of -the unbound (cation-free) and bound probe were calculated, including the influence of solute Solvent interactions, implicitly using a polarizable continuum model and exp-licitely employing the QM/MM approach. Because the results of the calculations indicate that many conformers of the probe are energetically accessible at room temperature in solution and hence contribute to the Signal, structurepteperty relationships were also taken into account. Results of our simulations-demonstrate that the one-photon absorption bands for both the unbound -and bound forms correspond to the bright pi -> pi* transition to the first excited state; which, on the other hand,. exhibits negligible two-photon activity. On the basis of the results of the quadratic respOnse calculations, we put forward-notion that it is the second excited state that gives the strong signal in the experimental nonlinear spectrum. To explain the differenCes in the two-photon absorption activity for the two lowest-lying excited states and nonlinear response enhancement upon binding, we employed the generalized few -state model including the ground, first, and- second excited states. The analysis of the optical channel suggests that the large two-photon response is due to the coordination -induced increase of the, transition- moment from the first to the second excited state.

  • 44. Bednarska, Joanna
    et al.
    Zalesny, Robert
    Tian, Guangjun
    Natarajan Arul, Murugan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Bartkowiak, Wojciech
    Nonempirical Simulations of Inhomogeneous Broadening of Electronic Transitions in Solution: Predicting Band Shapes in One- and Two-Photon Absorption Spectra of Chalcones2017In: Molecules, ISSN 1431-5157, E-ISSN 1420-3049, Vol. 22, no 10, article id 1643Article in journal (Refereed)
    Abstract [en]

    We have examined several approaches relying on the Polarizable Embedding (PE) scheme to predict optical band shapes for two chalcone molecules in methanol solution. The PE-TDDFT and PERI-CC2 methods were combined with molecular dynamics simulations, where the solute geometry was kept either as rigid, flexible or partly-flexible (restrained) body. The first approach, termed RBMD-PE-TDDFT, was employed to estimate the inhomogeneous broadening for subsequent convolution with the vibrationally-resolved spectra of the molecule in solution determined quantum-mechanically (QM). As demonstrated, the RBMD-PE-TDDFT/QM-PCM approach delivers accurate band widths, also reproducing their correct asymmetric shapes. Further refinement can be obtained by the estimation of the inhomogeneous broadening using the RBMD-PERI-CC2 method. On the other hand, the remaining two approaches (FBMD-PE-TDDFT and ResBMD-PE-TDDFT), which lack quantum-mechanical treatment of molecular vibrations, lead to underestimated band widths. In this study, we also proposed a simple strategy regarding the rapid selection of the exchange-correlation functional for the simulations of vibrationally-resolved one-and two-photon absorption spectra based on two easy-to-compute metrics.

  • 45. Bednarska, Joanna
    et al.
    Zalesny, Robert
    Wielgus, Malgorzata
    Jedrzejewska, Beata
    Puttreddy, Rakesh
    Rissanen, Kari
    Bartkowiak, Wojciech
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Osmialowski, Borys
    Two-photon absorption of BF2-carrying compounds: insights from theory and experiment2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 8, p. 5705-5708Article in journal (Refereed)
    Abstract [en]

    This communication presents a structure-property study of a few novel pyridine-based difluoroborate compounds with a N-BF2-O core, which exhibit outstanding fluorescence properties. To exploit their potential for two-photon bioimaging, relationships between the two-photon action cross section and systematic structural modifications have been investigated and unravelled.

  • 46. Belyanin, Maxim L.
    et al.
    Stepanova, Elena V.
    Valiev, Rashid R.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. National Research Tomsk Polytechnic University, Russian Federation.
    Filimonov, Victor D.
    Usov, Vladimir Y.
    Borodin, Oleg Y.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Design, synthesis and evaluation of a new Mn - Contrast agent for MR imaging of myocardium based on the DTPA-phenylpentadecanoic acid complex2016In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 665, p. 111-116Article in journal (Refereed)
    Abstract [en]

    In the present paper we describe the first synthesis and evaluation of a novel Mn (II) complex (DTPA-PPDA Mn (II)) which contains a C-15 fatty acid moiety that has high affinity to the heart muscle. The complexation energy of DTPA-PPDA Mn (II) evaluated by quantum chemistry methodology indicates that it essentially exceeds the corresponding value for the known DTPA Mn (II) complex. Molecular docking revealed that the affinity of the designed complex to the heart-type transport protein H-FABP well exceeds that of lauric acid. Phantom experiments in low-field MRI the designed contrast agent provides MR imaging comparable to gadopentetic acid.

  • 47.
    Bergstrand, Jan
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Liu, Qingyun
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Huang, Bingru
    Würth, Christian
    Resch-Genger, Ute
    Zhan, Qiuqiang
    Widengren, Jerker
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Ågren, Hans
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Liu, Haichun
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    On the decay time of upconversion luminescence2019In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 11, no 11, p. 4959-4969Article in journal (Refereed)
    Abstract [en]

    In this study, we systematically investigate the decay characteristics of upconversion luminescence (UCL) under anti-Stokes excitation through numerical simulations based on rate-equation models. We find that a UCL decay profile generally involves contributions from the sensitizer's excited-state lifetime, energy transfer and cross-relaxation processes. It should thus be regarded as the overall temporal response of the whole upconversion system to the excitation function rather than the intrinsic lifetime of the luminescence emitting state. Only under certain conditions, such as when the effective lifetime of the sensitizer's excited state is significantly shorter than that of the UCL emitting state and of the absence of cross-relaxation processes involving the emitting energy level, the UCL decay time approaches the intrinsic lifetime of the emitting state. Subsequently, Stokes excitation is generally preferred in order to accurately quantify the intrinsic lifetime of the emitting state. However, possible cross-relaxation between doped ions at high doping levels can complicate the decay characteristics of the luminescence and even make the Stokes-excitation approach fail. A strong cross-relaxation process can also account for the power dependence of the decay characteristics of UCL.

    Download full text (pdf)
    fulltext
  • 48. Birgerson, J.
    et al.
    Keil, M.
    Luo, Yi
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Svensson, S.
    Ågren, Hans
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Salaneck, W. R.
    A study of the electronic structure of ethylenedioxythiophene in gas phase using NEXAFS and quantum chemical calculations2004In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 392, no 1-3, p. 100-104Article in journal (Refereed)
    Abstract [en]

    Near-edge X-ray absorption fine structure spectroscopy spectra of ethylenedioxythiophene has been recorded in gas phase at the carbon K-edge, sulphur L-edge and oxygen, K-edge. The experimental data has been interpreted with the help of a modified density functional code deMon. The good agreement between the calculated spectra and the measured one allows us to assign all observed resonances. The existence of pi* resonances in both the measured and the calculated OK-edge adsorption spectrum demonstrate that the delocalized pi-system of the thiophene part of the molecule is extended up to the oxygen atoms of the molecule.

  • 49. Bjorneholm, O.
    et al.
    Bassler, M.
    Ausmees, A.
    Hjelte, I.
    Feifel, R.
    Wang, H.
    Miron, C.
    Piancastelli, M. N.
    Svensson, S.
    Sorensen, S. L.
    Gel'mukhanov, Faris
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments (pre-2005), Biotechnology.
    Doppler splitting of in-flight auger decay of dissociating oxygen molecules: The localization of delocalized core holes2000In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 84, no 13, p. 2826-2829Article in journal (Refereed)
    Abstract [en]

    By exploiting the core-excitation-induced dissociation of O-2, we find that the Auger emission exhibits a Doppler-like energy shift. We show this to be a manifestation of localization of the core hole and propose that the problem of core-hole localization versus delocalization in core-hole spectroscopies may be resolved by considering the nature of the measurement.

  • 50.
    Bondesson, Laban
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Frediani, Luca
    Department of Chemistry, University of Tromsø, Norway.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Mennucci, Bendetta
    Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Italy.
    Solvation of N3- at the water surface: the Polarizable Continuum Model approach2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 23, p. 11361-11368Article in journal (Refereed)
    Abstract [en]

    We present a new quantum mechanical model to introduce Pauli repulsion interaction between a molecular solute and the surrounding solvent in the framework of the Polarizable Continuum Model. The new expression is derived in a way to allow naturally for a position-dependent solvent density. This development makes it possible to employ the derived expression for the calculation of molecular properties at the interface between two different dielectrics. The new formulation has been tested on the azide anion (N-3(-)) for which we have calculated the solvation energy, the dipole moment, and the static polarizability at the interface as a function of the ion position. The calculations have been carried out for different ion-surface orientations, and the results have also been compared with the parallel electrostatic-only solvation model.

1234567 1 - 50 of 728
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf