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  • 51.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hede, Thomas
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Leck, Caroline
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Cloud droplet activation mechanisms of amino acid aerosol particles: insight from molecular dynamics simulations2013In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, p. 65-Article in journal (Refereed)
    Abstract [en]

    Atmospheric amino acids constitute a large fraction of water-soluble organic nitrogen compounds in aerosol particles, and have been confirmed as effective cloud condensation nuclei (CCN) materials in laboratory experiments. We present a molecular dynamics (MD) study of six amino acids with different structures and chemical properties that are relevant to the remote marine atmospheric aerosol-cloud system, with the aim of investigating the detailed mechanism of their induced changes in surface activity and surface tension, which are important properties for cloud drop activation. Distributions and orientations of the amino acid molecules are studied; these L-amino acids are serine (SER), glycine (GLY), alanine (ALA), valine (VAL), methionine (MET) and phenylalanine (PHE) and are categorised as hydrophilic and amphiphilic according to their affinities to water. The results suggest that the presence of surface-concentrated amphiphilic amino acid molecules give rise to enhanced Lennard-Jones repulsion, which in turn results in decreased surface tension of a planar interface and an increased surface tension of the spherical interface of droplets with diameters below 10 nm. The observed surface tension perturbation for the different amino acids under study not only serves as benchmark for future studies of more complex systems, but also shows that amphiphilic amino acids are surface active. The MD simulations used in this study reproduce experimental results of surface tension measurements for planar interfaces and the method is therefore applicable for spherical interfaces of nano-size for which experimental measurements are not possible to conduct.

  • 52.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Hede, Thomas
    Tu, Yaoquan
    Leck, Caroline
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Molecular Dynamics Study on the Surface Tension of Atmospheric Water Droplets Containing Amino AcidsManuscript (preprint) (Other academic)
    Abstract [en]

    Atmospheric amino acids constitute an important fraction of the water-soluble organic nitrogen compounds in both marine and continental aerosols, and have been confirmed as effective cloud condensation nuclei materials in laboratory tests. We here present molecular dynamics study of six types of amino acids in atmospheric water droplets, in order to investigate molecular distributions, orientations and induced changes in surface tension, and to evaluate their indirect effects on optical properties of clouds. These amino acids, including serine, glycine, alanine, valine, methionine and phenylalanine, are categorized into hydrophilic and hydrophobic species according to their affinities to water. Different amino acids show distinct effects on the surface tension; even the same amino acid has different influence on the surface tension of planar and spherical interfaces. Finally the curvature dependence of the surface tension is modeled by a quadratic polynomial function of the inverse of droplet radius, and such relationship is used to improve the Köhler equation in predicting the critical supersaturation of droplet activation.

  • 53.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Hede, Thomas
    Tu, Yaoquan
    Leck, Caroline
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Surface-Active cis-Pinonic Acid in Atmospheric Droplets: A Molecular Dynamics Study2010In: The Journal of Physical Chemistry Letters, E-ISSN 1948-7185, Vol. 1, no 4, p. 769-773Article in journal (Refereed)
    Abstract [en]

    Water vapor in the atmosphere can condensate and form cloud droplets when there is a certain amount of humidity and a presence of cloud condensation nuclei, and organic solutes called surfactants can significantly lower the surface tension of water-one of the parameters determining cloud droplet population. We here present a molecular dynamics study of the behavior of cis-pinonic acid, a commonly found organic compound in cloud condensation nuclei, and its effect on the surface tension of water clusters. Specifically, the decrease in surface tension is found to depend on not only the concentration of the organic compound but also the droplet size due to the spontaneous assembly of the surfactant molecules on the droplet surface. This leads to the conclusion that the partitioning of the surfactant between the bulk and surface plays an important role in the behavior of atmospheric aerosol particles and thus in their availability for cloud formation.

  • 54.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hua, Weijie
    Wang, Bo-Yao
    Pong, Way-Faung
    Glans, Per-Anders
    Guo, Jinghua
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Dopant Size Dependent Electronic Structure of Boron Nitride-Doped GrapheneManuscript (preprint) (Other academic)
  • 55.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Hua, Weijie
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wang, Bo-Yao
    Pong, Way-Faung
    Glans, Per-Anders
    Guo, Jinghua
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Effects of domain size on x-ray absorption spectra of boron nitride doped graphenes2016In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, no 8, article id 081601Article in journal (Refereed)
    Abstract [en]

    Doping is an efficient way to open the zero band gap of graphene. The control of the dopant domain size allows us to tailor the electronic structure and the properties of the graphene. We have studied the electronic structure of boron nitride doped graphenes with different domain sizes by simulating their near-edge X-ray absorption fine structure (NEXAFS) spectra at the N K-edge. Six different doping configurations (five quantum dot type and one phase-separated zigzag-edged type) were chosen, and N K-edge NEXAFS spectra were calculated with large truncated cluster models by using the density functional theory with hybrid functional and the equivalent core hole approximation. The opening of the band gap as a function of the domain size is revealed. We found that nitrogens in the dopant boundary contribute a weaker, red-shifted pi* peak in the spectra as compared to those in the dopant domain center. The shift is related to the fact that these interfacial nitrogens dominate the lowest conduction band of the system. Upon increasing the domain size, the ratio of interfacial atom decreases, which leads to a blue shift of the pi* peak in the total NEXAFS spectra. The spectral evolution agrees well with experiments measured at different BN-dopant concentrations and approaches to that of a pristine h-BN sheet.

  • 56.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Kao, Fu-Jen
    Chuang, Chien-Chin
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Enhancing fluorescence of quantum dots by silica-coated gold nanorods under one- and two-photon excitation2010In: Optics Express, E-ISSN 1094-4087, Vol. 18, no 11, p. 11335-11346Article in journal (Refereed)
    Abstract [en]

    Nano-composites of quantum dots (QDs) and gold nanorods (GNRs) or silica-coated GNRs (GNRs_SiO2) were synthesized. The attached GNRs modify the excitation intensity and spontaneous emission of QDs through the surface plasmonic effects. The fluorescence from QDs is enhanced and can be optimized by modifying the thickness of silica coated on GNRs, under both one-and two-photon excitations. The measurements of fluorescence intensity and lifetime demonstrate that the enhancement may be attributed to the matching of the localized surface plasmon resonance of GNR to the excitation wavelength. In addition to enhancing QD-fluorescence in QD-GNR@SiO2, GNRs also present as an effective contrast agent for bio-imaging, through light scattering and or two-photon emission, as well as for photo-thermal therapy. The composite's multifunctional characteristics are highly valuable and to be exploited in bio-applications. (C) 2010 Optical Society of America

  • 57.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Leck, Caroline
    Sun, Lu
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hede, Thomas
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Cross-Linked Polysaccharide Assemblies in Marine Gels: An Atomistic Simulation2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 16, p. 2637-2642Article in journal (Refereed)
    Abstract [en]

    Marine polymeric gels or colloidal nano- and microgels have been shown to contribute significantly to the primary marine aerosol and cloud condensation nuclei over remote marine areas. A microscopic understanding of such biologically derived matter at the sea air interface is important for future development of global climate models, but unfortunately cannot be obtained from modern characterization techniques. In this contribution, we employ molecular dynamics simulations to reveal the atomistic details of marine polymeric gels represented by anionic polysaccharide assemblies. The ionic bonds formed between polysaccharides and metal ions in seawater as well as the hydrophobic contribution to surface area are investigated in detail, and destabilization of the assemblies upon removal of Ca2+ or acidification is explained. These results provide insight into physicochemical properties of polysaccharide-Ca2+ structures and enable future studies of their roles of in the wetting process of cloud droplet activation.

  • 58.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Wenlong
    E China Univ Sci & Technol, Key Lab Adv Mat, Shanghai 200237, Peoples R China.;E China Univ Sci & Technol, Inst Fine Chem, Shanghai Key Lab Funct Mat Chem, Shanghai 200237, Peoples R China..
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tian, He
    E China Univ Sci & Technol, Key Lab Adv Mat, Shanghai 200237, Peoples R China.;E China Univ Sci & Technol, Inst Fine Chem, Shanghai Key Lab Funct Mat Chem, Shanghai 200237, Peoples R China..
    Zhu, Weihong
    E China Univ Sci & Technol, Key Lab Adv Mat, Shanghai 200237, Peoples R China.;E China Univ Sci & Technol, Inst Fine Chem, Shanghai Key Lab Funct Mat Chem, Shanghai 200237, Peoples R China..
    Theoretical insight into the enhanced hindrance, thermal stability and optical properties of diarylethene with a benzobis(thiadiazole) bridge and benzothiophene rings2016In: Dyes and pigments, ISSN 0143-7208, E-ISSN 1873-3743, Vol. 125, p. 348-355Article in journal (Refereed)
    Abstract [en]

    To rationalize the effects of intramolecular steric hindrance on the performance of diarylethene photoswitches, we here present a density functional theory study on the thermal bistability and optical properties of a photochromic diarylethene BBTE consisting of a benzobis(thiadiazole) bridge and benzothiophene rings, in which prominent steric hindrance exists owing to the extended structures of is-conjugated groups. Our calculations not only provide rational explanations for the isolation of enantiopure anti-parallel conformers of the open-ring isomer, but also elucidate the detailed pathway of a two-step ground-state ring-opening process, where the thermal stability of the closed-ring isomer is guaranteed by an overall free energy barrier of around 113 kJ mol(-1) (27 kcal mol(-1)). In addition, the tunable intramolecular charge transfer of the donor acceptor structure formed by the benzobis(thiadiazole) bridge and the bulky benzothiophene rings is also addressed within time-dependent density functional theory. Charge transfer excitations in the open- and the closed-ring isomers are characterized as long-range and medium-range, respectively. We show that the diarylethene derivative under investigation can serve as a promising platform for future development of optoelectronic materials.

  • 59.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Minaev, Boris F.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Tian, He
    E China Univ Sci & Technol, Adv Mat Lab, Shanghai 200237, Peoples R China.;E China Univ Sci & Technol, Inst Fine Chem, Shanghai 200237, Peoples R China..
    Density Functional Theory Study of Photophysical Properties of Iridium(III) Complexes with Phenylisoquinoline and Phenylpyridine Ligands2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 42, p. 20724-20731Article in journal (Refereed)
    Abstract [en]

    Linear and quadratic response time-dependent density functional theory is applied to study the photophysical properties of iridium complexes with phenylisoquinoline and phenylpyridine ligands. The ground-state geometries, frontier molecular orbitals, absorption spectra, phosphorescence wavelengths, and radiative rate constants are computed to facilitate better understanding of the structure-property relationships of these iridium complexes used in organic light-emitting diodes (OLEDs) to enhance spin-orbit coupling and triplet state emission. The agreement obtained between calculated and available experimental data indicates a possibility to guide the design of phosphorescence-based OLEDs by predicting their relevant properties through quantum mechanical calculations.

  • 60.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Minaev, Boris F.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tian, He
    E China Univ Sci & Technol, Key Lab Adv Mat, Shanghai 200237, Peoples R China.;E China Univ Sci & Technol, Inst Fine Chem, Shanghai 200237, Peoples R China..
    Theoretical Study of Phosphorescence of Iridium Complexes with Fluorine-Substituted Phenylpyridine Ligands2011In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, no 16, p. 2517-2524Article in journal (Refereed)
    Abstract [en]

    Time-dependent density functional theory (TD-DFT) with linear and quadratic response approaches was applied to calculate absorption and luminescence spectra of a number of facial and meridional iridium complexes with fluorine-substituted phenylpyridine (F(n)ppy) ligands. The absorption and luminescence spectra were studied to simulate the photophysical properties of electroluminescent devices fabricated on the basis of these iridium complexes used to increase spin-orbit coupling and the triplet-state blue emission of the corresponding organic light-emitting diodes (OLEDs). By using the quadratic response technique, the phosphorescence radiative rate constant and lifetime of the studied iridium complexes were calculated through spin-orbit coupling perturbation and compared with the measured data in experiments. A satisfactory agreement between these data permits us to guide improvements in the design of phosphorescence-based OLEDs by predicting the structure-property relationships through quantum chemical calculations.

  • 61.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Prendergast, David
    Guo, Jinghua
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Electronic Structure of Lithium Intercalated Graphite from First-Principles SimulationsManuscript (preprint) (Other academic)
  • 62.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Kongsted, Jacob
    Natarajan Arul, Murugan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Binding Mechanism and Magnetic Properties of a Multifunctional Spin Label for Targeted EPR Imaging of Amyloid Proteins: Insight from Atomistic Simulations and First-Principles Calculations2012In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 8, no 11, p. 4766-4774Article in journal (Refereed)
    Abstract [en]

    Electron paramagnetic resonance (EPR) imaging techniques provide a promising approach to detect amyloid structures which are of paramount importance in early-stage diagnosis of conformational diseases. Here, we report a combined molecular dynamics and density functional theory/molecular mechanics computational scheme for evaluation of the binding mechanism between a multifunctional spin label and the target amyloid protein. In addition, we consider evaluation of EPR spin Hamiltonian parameters with the aim of providing a better microscopic understanding and interpretation of EPR spectroscopy. The results from molecular dynamics simulations suggest that the oligothiophene conjugate part of the spin label interacts with hydrophobic residues of the amyloid protein through hydrophobic attraction and that both the N-O bond length and the N-O out-of-plane tilt angle in the nitroxide group are slightly diminished after, complexation with the protein. The translational and rotational motions of the protein bound spin label are considerably slowed compared to those of the free spin label in aqueous solution, but interestingly, hydrogen bonds formed between the nitroxide oxygen group and the surrounding water molecules are hardly affected by the presence Of the amyloid protein. First principles calculation's suggest that EPR spin Hamiltonian parameters including the nitroxide nitrogen hyperfine coupling tensor A(N) and electronic g tensor suffer noticeable changes upon complexation with the protein. The magnitude of the A(N) tensor is found,to:be. closely related to the nitroxide N-O out tilt angle, while the g tensor is affected by both the nitroxide N-O bond length as well as the interaction between the spin label and the amyloid protein With this work we show that state-of-the-art simulation techniques represent a promising way of providing a detailed understanding of the microscopic mechanisms responsible for the formation and stability of a spin label complexed with amyloid structures as well as the magnetic properties of the free and protein-bound spin label.

  • 63.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Tu, Yaoquan
    Tian, He
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Nuclear magnetic shielding of the Cd-113(II) ion in aqua solution: A combined molecular dynamics/density functional theory study2008In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 112, no 36, p. 11347-11352Article in journal (Refereed)
    Abstract [en]

    We present a combined molecular dynamics simulation and density functional theory investigation of the nuclear magnetic shielding constant of the Cd-113(II) ion solvated in aqueous solution. Molecular dynamics simulations are carried out for the cadmium-water system in order to produce instantaneous geometries for subsequent determination of the nuclear magnetic shielding constant at the density functional theory level. The nuclear magnetic shielding constant is computed using a perturbation theory formalism, which includes nonrelativistic and leading order relativistic contributions to the nuclear magnetic Shielding tensor. Although the NMR shielding constant varies significantly with respect to simulation time, the value averaged over increasing number of snapshots remains almost constant. The paramagnetic nonrelativistic contribution is found to be most sensitive to dynamical changes in the system and is mainly responsible for the thermal and solvent effects in solution. The relativistic correction features very little sensitivity to the chemical environment, and can be disregarded in theoretical calculations when a Cd complex is used as reference compound in Cd-113 NMR experiments, due to the mutual cancelation between individual relativistic corrections.

  • 64.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Tu, Yaoquan
    Tian, He
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Paramagnetic Perturbation of the F-19 NMR Chemical Shift in Fluorinated Cysteine by O-2: A Theoretical Study2009In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 31, p. 10916-10922Article in journal (Refereed)
    Abstract [en]

    We present a combined molecular dynamics and density functional theory study of dioxygen-induced perturbation of the F-19 NMR chemical shifts in an aqueous solution of fluorinated cysteine under 100 atm of O-2 partial pressure. Molecular dynamics Simulations are carried out to determine the dominant structures of O-2 and the fluorinated cysteine complexes in water, and the collected structural information is exploited in computation of F-19 chemical shifts using density functional theory. The obtained results indicate that the density redistribution of the O-2 unpaired electrons between the dioxygen and fluorinated cysteine is responsible for the experimentally observed perturbation of the F-19 NMR chemical shifts, where the Fermi contact interaction plays the key role. The O-2-induced paramagnetic F-19 chemical shift, averaged over the simulation trajectory, is comparable with the reported experimental values, proving the availability of the developed strategy for modeling F-19 NMR chemical shifts in the presence of paramagnetic agents in ail aqueous solution. The applicability of the combined molecular dynamics/density functional theory approach for dioxygen NMR perturbation to all resonating nuclei including H-1, C-13, N-15, and F-19 is emphasized, and the ramification of this for investigations of membrane protein structures is discussed.

  • 65.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Electronic Circular Dichroism of Surface-Adsorbed Molecules by Means of Quantum Mechanics Capacitance Molecular Mechanics2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 11, p. 5833-5840Article in journal (Refereed)
    Abstract [en]

    To promote a more comprehensive understanding of the influence of metal-adsorbate interaction for molecules at metallo surfaces or metallo nanoparticles in solvent environments on their electronic circular dichroism (ECD) spectra, we evaluate the application of a recently derived quantum mechanics capacitance molecular mechanics (QMCMM) model for ECD. Using helicene absorbed on gold surfaces in protic and aprotic solvents as illustration, we elucidate the detailed effects on excitation energies, transition moments, rotatory strengths, orientation dependence of ECD spectra, and the different roles of aprotic and protic solvents and the induced charge distribution patterns on the surface. These changes are decomposed in terms of surface alone, solvent alone, and combined surface solvent influence, and furthermore into the indirect contributions by the surface-induced restructuring of the helicene. Much of the salient changes of the ECD can be rationalized to the substantial redistribution of charge at the gold surface induced by the presence of the helicene. The study indicates that through the QMCMNI model the effects of a metallic surface on the circular dichroism spectra of adsorbed organic molecules can be tackled by extended QM calculations coupled to polarizability-capacitance force fields for large metallic clusters representing surfaces or nanoparticles.

  • 66.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Two-Photon Absorption of Metal-Assisted Chromophores2014In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 10, no 12, p. 5630-5639Article in journal (Refereed)
    Abstract [en]

    Aiming to understand the effect of a metal surface on nonlinear optical properties and the combined effects of surface and solvent environments on such properties, we present a multiscale response theory study, integrated with dynamics of the two-photon absorption of 4-nitro-4'-amino-trans-stilbene physisorbed on noble metal surfaces, considering two such surfaces, Ag(111) and Au(111), and two solvents, cyclohexane and water, as cases for demonstration. A few conclusions of general character could be drawn: While the geometrical change of the chromophore induced by the environment was found to notably alter (diminish) the two-photon absorption cross section in the polar medium, the effects of the metal surface and solvent on the electronic structure of the chromophore surpasses the geometrical effects and leads to a considerably enhanced two-photon absorption cross section in the polar solvent. This enhancement of two-photon absorption arises essentially from the metal charge image induced enlargement of the difference between the dipole moment of the excited state and the ground state. The orientation-dependence of the two-photon absorption is found to connect with the lateral rotation of the chromophore, where the two-photon absorption reaches its maximum when the polarization of the incident light coincides with the long-axis of the chromophore. Our results demonstrate a distinct enhancement of the two-photon absorption by a metal surface and a polar medium and envisage the employment of metal-chromophore composite materials for future development of nonlinear optical materials with desirable properties.

  • 67.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Tu, Yaoquan
    Tian, He
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Computer simulations of aqua metal ions for accurate reproduction of hydration free energies and structures2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, no 10, p. 104505-Article in journal (Refereed)
    Abstract [en]

    Metal ions play essential roles in biological processes and have attracted much attention in both experimental and theoretical fields. By using the molecular dynamics simulation technology, we here present a fitting-refining procedure for deriving Lennard-Jones parameters of aqua metal ions toward the ultimate goal of accurately reproducing the experimentally observed hydration free energies and structures. The polarizable SWM4-DP water model {proposed by Lamoureux [J. Chem. Phys. 119, 5185 (2003)]} is used to properly describe the polarization effects of water molecules that interact with the ions. The Lennard-Jones parameters of the metal ions are first obtained by fitting the quantum mechanical potential energies of the hexahydrated complex and are subsequently refined through comparison between the calculated and experimentally measured hydration free energies and structures. In general, the derived Lennard-Jones parameters for the metal ions are found to reproduce hydration free energies accurately and to predict hydration structures that are in good agreement with experimental observations. Dynamical properties are also well reproduced by the derived Lennard-Jones parameters.

  • 68.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Zhang, Qiong
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Tu, Yaoquan
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Tian, He
    Modulation of iridium(III) phosphorescence via photochromic ligands: a density functional theory study2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 41, p. 13730-13736Article in journal (Refereed)
    Abstract [en]

    The photochromic iridium(III) complex (Py-BTE)(2)Ir(acac) synthesized by Tan et al. [W. Tan et al., Org. Lett. 2009, 11, 161-164] has shown distinct photo-reactivity and photo-controllable phosphorescence. We here present a density functional theory study on the (Py-BTE)(2)Ir(acac) complex to explore the mechanism at the molecular level and to help further design of photochromic iridium(III) complexes with the desirable properties. The hybrid functional PBE0, with 25% Hartree-Fock exchange, is found to give an optimal structure compared with X-ray crystallographic data. The absorption bands are well reproduced by using time-dependent density functional theory calculations, lending the possibility to assign the metal-to-ligand and intra-ligand charge transfer transitions. The radiative and nonradiative deactivation rate constants, k(r) and k(nr), are rationalized for both the open-ring and closed-ring forms of the complex. The very large k(nr) and small k(r) make the closed-ring form of the complex non-emissive. The triplet reactivity of the Py-BTE ligand is also studied by performing density functional theory calculations on the potential energy surfaces of the ground state and the lowest triplet state.

  • 69.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhu, Liangliang
    Duan, Sai
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhao, Yanli
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Aggregation-induced chiral symmetry breaking of a naphthalimide-cyanostilbene dyad2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 43, p. 23854-23860Article in journal (Refereed)
    Abstract [en]

    Spontaneously emerged supramolecular chirality and chiral symmetry breaking from achiral/racemic constituents remain poorly understood. We here report that supramolecular chirality may emerge from the structural flexibility of achiral aryl nitrogen centres which provide instantaneous chirality. Employing a naphthalimide-cyanostilbene dyad as a model, we explored the underlying mechanism of aggregation-induced chiral symmetry breaking and found that the conformations of the N-naphthylpiperazine and the N, N-dimethylaniline units facilitate the formation of ordered supramolecular structures and offer opposite handedness. Furthermore, chiral symmetry breaking of the monomers was amplified by the formation of dimers. The microscopic and the macroscopic observations from the theoretical simulations and experimental measurements are thus rationalized by connecting the population of the dihedral angles of the aryl nitrogen centres, the morphology of the self-assemblies, and the observed circular dichroism spectra.

  • 70.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zou, Qi
    Shanghai Univ Elect Power, Shanghai Key Lab Mat Protect & Adv Mat Elect Powr, Shanghai 200090, Peoples R China..
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Photochromic Diarylethenes with Heterocyclic Aromatic Rings: Correlation between Thermal Bistability and Geometrical Characters of Transition States2015In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 119, no 34, p. 9140-9147Article in journal (Refereed)
    Abstract [en]

    We present a density functional theory study on the thermal bistability of a number of photochromic diarylethenes, with emphasis on the free energy barrier of the ground-state ring-opening process. We found that the free energy barrier is correlated with the geometrical and vibrational character of the transition state, in particular the distance between the two reactive carbon atoms, the out-of-plane angles of the methyl groups at the reactive carbon atoms, and the imaginary vibrational frequency. Based on these relationships we propose a linear fitting expression for the free energy barrier in terms of the three aforementioned transition-state quantities and obtained a correlation coefficient of R-2 = 0.971. In this way quantum chemical calculations may provide insight and structure property relationships, which can be applied in the development of novel photochromic materials.

  • 71.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Molecular Dynamics Simulations Using a Capacitance-Polarizability Force Field2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 33, p. 19430-19437Article in journal (Refereed)
    Abstract [en]

    We present molecular dynamics (MD) simulations using a capacitance-polarizability force field. This force field allows an atomistic description of charge migration within a particle and hence the image charge effects at the interface of such a particle. By employing atomic capacitance and polarizability as the key parameters that describe fluctuating charges and dipoles, we can thus explore the effect of charge migration on the structural dynamics. We illustrate the method by exploring gold nanoparticles in aqueous solutions and compare with previous simulation work. We reach the conclusion that the capacitance polarizability force field MD method serves as a promising tool for simulating gold water systems, indicating probable extensions to other metal solutions and for studies of more complicated systems provided that a proper parametrization of the capacitance force field can be made. For the particular system studied, it is found that the water molecules interact with the surface through oxygen atoms, leading to more hydrogen-bond donors than acceptors at the gold water interface. A prominent shoulder peak is found in the radial distribution of oxygen atoms with respect to the gold surface, due to the fact that the oxygen atoms adsorbed at the on-top sites of the gold nanoparticle. The surface of the aqueous gold nanoparticle carries negative charge, which is balanced by the positive charge in the second outermost layer.

  • 72. Li, Xing
    et al.
    Yu, Fengtao
    Stappert, Sebastian
    Li, Chen
    Zhou, Ying
    Yu, Ying
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Agren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hua, Jianli
    Tian, He
    Enhanced Photocurrent Density by Spin-Coated NiO Photocathodes for N-Annulated Perylene-Based p-Type Dye-Sensitized Solar Cells2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 30, p. 19393-19401Article in journal (Refereed)
    Abstract [en]

    The low photocurrent density of p-type dye sensitized solar cells (p-DSSCs) has limited the development of high-efficiency tandem cells due to the inadequate light harvesting ability of sensitizers and the low hole mobility of semiconductors. Hereby, two new "push-pull" type organic dyes (PQ-1 and PQ-2) containing N-annulated perylene as electron donor have been synthesized, where the PQ-2-based p-DSSCs show higher photoelectric conversion efficiency (PCE) of 0.316% owing to the higher molar extinction compared to of that PQ-1. Additionally, the photocurrent densities were remarkably increased from 2.20 to 5.85 mA cm(-2) for PQ-1 and 2.45 to 6.69 mA cm(-2) for PQ-2 by spin coated NiO photocathode based-p-DSSCs, respectively. This results are ascribed to the enhancement of hole transport rate, dye loading amounts and transparency of NiO films in comparison to that prepared by screen-printing method. Electrochemical impedance spectroscopy and theoretical calculations studies indicate that the molecular dipole moment approaching closer to the NiO surface shifts the quasi-Fermi level to more positive levels, improving,open-circuit voltage (V-oc). Intensity-modulated photocurrent spectroscopy illustrates that the hole transit time in NiO films prepared in spin-coating is shorter than that prepared by screen-printing method.

  • 73. Liang, Lijun
    et al.
    Li, Xin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Theoretical insights into aggregation-induced helicity modulation of a perylene bisimide derivative2018In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 24, no 3, article id 51Article in journal (Refereed)
    Abstract [en]

    Formation of helical chiroptical self-assemblies via noncovalent interaction is a widely observed phenomenon in nature, the mechanism of which remains insufficiently understood. Employing an amphiphilic perylene-sugar dyad molecule (PBI-HAG) as an example, we report that the modulatable supramolecular helicity may emerge from an aggregating process that is dominated by competition between two types of noncovalent interaction: hydrogen bonding and pi-pi stacking. The interplay between these two driving forces, which is greatly affected by the solvent environment, determines the morphology the supramolecular assembly of PBI-HAGs. In particular, a non-layered supramolecular structure was formed in octane owing to stabilization effects of intermolecular hydrogen bonds, whereas a layered supramolecular structure was formed in water because of energetically favorable pi-pi stacking of aromatic rings. The formation of distinct supramolecular architectures in different solvents was reinforced by simulated circular dichroism spectra, which show opposite signals consistent with experimental observations. The results of this study could help us understand aggregation-induced supramolecular chirality of noncovalent self-assemblies.

  • 74. Lim, Chang-Keun
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Yue
    Drew, Kurt L. M.
    Palafox-Hernandez, J. Pablo
    Tang, Zhenghua
    Baev, Alexander
    Kuzmin, Andrey N.
    Knecht, Marc R.
    Walsh, Tiffany R.
    Swihart, Mark T.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Prasad, Paras N.
    Plasmon-enhanced two-photon-induced isomerization for highly-localized light-based actuation of inorganic/organic interfaces2016In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 8, no 7, p. 4194-4202Article in journal (Refereed)
    Abstract [en]

    Two-photon initiated photo-isomerization of an azobenzene moiety adsorbed on silver nanoparticles (Ag NPs) is demonstrated. The azobenzene is linked to a materials-binding peptide that brings it into intimate contact with the Ag NP surface, producing a dramatic enhancement of its two-photon absorbance. An integrated modeling approach, combining advanced conformational sampling with Quantum Mechanics/Capacitance Molecular Mechanics and response theory, shows that charge transfer and image charges in the Ag NP generate local fields that enhance two-photon absorption of the cis isomer, but not the trans isomer, of adsorbed molecules. Moreover, dramatic local field enhancement is expected near the localized surface plasmon resonance (LSPR) wavelength, and the LSPR band of the Ag NPs overlaps the azobenzene absorbance that triggers cis to trans switching. As a result, the Ag NPs enable two-photon initiated cis to trans isomerization, but not trans to cis isomerization. Confocal anti-Stokes fluorescence imaging shows that this effect is not due to local heating, while the quadratic dependence of switching rate on laser intensity is consistent with a two-photon process. Highly localized two-photon initiated switching could allow local manipulation near the focal point of a laser within a 3D nanoparticle assembly, which cannot be achieved using linear optical processes.

  • 75.
    Lin, Lili
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Shandong Normal Univ, Coll Phys & Elect, China.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tian, Guangjun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Geng, Hua
    Shuai, Zhigang
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, China.
    First-principles investigations on the anisotropic charge transport in 4,4 '-bis((E)-2-(naphthalen-2-yl)vinyl)-1,1 '-biphenyl single crystal2014In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 133, no 9, p. 1551-Article in journal (Refereed)
    Abstract [en]

    We applied the master equation method to investigate the anisotropic transport property of the 4,4'-bis((E)-2-(naphthalen-2-yl)vinyl)-1,1'-biphenyl molecular crystal based on first-principles calculation. It is found that the hole mobility has the largest value along the [100] direction, while electrons have the best transport property along the [010] direction. The anisotropic transport property was found to have close relationship with the charge transfer integral which is determined by the molecular stacking network in the crystals as well as the intermolecular frontier orbital overlap. In addition, the effect of the charge carrier density and the electronic field on the charge transport was also studied, and little effect was found except that the density is larger than 0.01 and the electronic field is increased to 1.0 x 106 V/cm. The kinetic Monte Carlo simulation method has also been used to study the anisotropic charge transport property, and consistent results were obtained as with the master equation method.

  • 76. Liu, Guofeng
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sheng, Jianhui
    Li, Pei-Zhou
    Ong, Wee Kong
    Phua, Soo Zeng Fiona
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhu, Liangliang
    Zhao, Yanli
    Helicity Inversion of Supramolecular Hydrogels Induced by Achiral Substituents2017In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 11, no 12, p. 11880-11889Article in journal (Refereed)
    Abstract [en]

    Probing the supramolecular chirality of assemblies and controlling their handedness are closely related to the origin of chirality at the supramolecular level and the development of smart materials with desired handedness. However, it remains unclear how achiral residues covalently bonded to chiral amino acids can function in the chirality inversion of supramolecular assemblies. Herein, we report macroscopic chirality and dynamic manipulation of chiroptical activity of hydrogels self-assembled from phenylalanine derivatives, together with the inversion of their handedness achieved solely by exchanging achiral substituents between oligo(ethylene glycol) and carboxylic acid groups. This helicity inversion is mainly induced by distinct stacking mode of the self-assembled building blocks, as collectively confirmed by scanning electron microscopy, circular dichroism, crystallography, and molecular dynamics calculations. Through this straightforward approach, we were able to invert the handedness of helical assemblies by merely exchanging achiral substituents at the terminal of chiral gelators. This work not only presents a feasible strategy to achieve the handedness inversion of helical nanostructures for better understanding of chiral self-assembly process in supramolecular chemistry but also facilities the development of smart materials with controllable handedness in materials science.

  • 77. Loytynoja, T.
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Jankala, K.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Quantum mechanics capacitance molecular mechanics modeling of core-electron binding energies of methanol and methyl nitrite on Ag(111) surface2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, no 2, article id 024703Article in journal (Refereed)
    Abstract [en]

    We study a newly devised quantum mechanics capacitance molecular mechanics ( QMCMM) method for the calculation of core-electron binding energies in the case of molecules adsorbed on metal surfaces. This yet untested methodology is applied to systems with monolayer of methanol/methyl nitrite on an Ag(111) surface at 100 K temperature. It was found out that the studied C, N, and O 1s core-hole energies converge very slowly as a function of the radius of the metallic cluster, which was ascribed to build up of positive charge on the edge of the Ag slab. Further analysis revealed that an extrapolation process can be used to obtain binding energies that deviated less than 0.5 eV against experiments, except in the case of methanol O 1s where the difference was as large as 1.8 eV. Additional QM-cluster calculations suggest that the latter error can be connected to the lack of charge transfer over the QM-CMM boundary. Thus, the results indicate that the QMCMM and QM-cluster methods can complement each other in a holistic picture of molecule-adsorbate core-ionization studies, where all types of intermolecular interactions are considered.

  • 78.
    Lu, Yunyue
    et al.
    East China Univ Sci & Technol, Sch Chem & Mol Engn, Key Lab Adv Mat, Shanghai 200237, Peoples R China.;East China Univ Sci & Technol, Sch Chem & Mol Engn, Inst Fine Chem, Shanghai 200237, Peoples R China..
    Song, Heli
    East China Univ Sci & Technol, Sch Chem & Mol Engn, Key Lab Adv Mat, Shanghai 200237, Peoples R China.;East China Univ Sci & Technol, Sch Chem & Mol Engn, Inst Fine Chem, Shanghai 200237, Peoples R China..
    Li, Xin
    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.
    Liu, Qingyun
    Shandong Univ Sci & Technol, Coll Chem & Environm Engn, Qingdao 266510, Peoples R China..
    Zhang, Jiwei
    Donghua Univ, Coll Chem Chem Engn & Biotechnol, Shanghai 201620, Peoples R China..
    Zhang, Xuan
    Donghua Univ, Coll Chem Chem Engn & Biotechnol, Shanghai 201620, Peoples R China..
    Xie, Yongshu
    East China Univ Sci & Technol, Sch Chem & Mol Engn, Key Lab Adv Mat, Shanghai 200237, Peoples R China.;East China Univ Sci & Technol, Sch Chem & Mol Engn, Inst Fine Chem, Shanghai 200237, Peoples R China..
    Multiply Wrapped Porphyrin Dyes with a Phenothiazine Donor: A High Efficiency of 11.7% Achieved through a Synergetic Coadsorption and Cosensitization Approach2019In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 5, p. 5046-5054Article in journal (Refereed)
    Abstract [en]

    Photocurrent (J) and photovoltage (Vac) are two important parameters for dye-sensitized solar cells (DSSCs) to achieve high power conversion efficiencies (PCEs). Herein, we synthesize four novel porphyrin dyes, XW36 XW39, using an N-phenyl-substituted phenothiazine donor to pursue higher PCE. For XW36 and XW37, the N-phenyl group is wrapped with two ortho-alkoxy chains. In contrast, it is substituted with a para-alkoxy group in XW38 and XW39. The phenothiazine wrapping in XW36 and XW37 induces more serious distortion, which is beneficial for anti-aggregation but unfavorable for the electron transfer from donor to a porphyrin framework. Thus, individual porphyrin dyes XW36 and XW37 exhibit efficiencies of 9.05 and 9.58%, respectively, lower than those of 9.51 and 10.0% achieved for XW38 and XW39, respectively. Besides, the introduction of a methyl group into a benzoic acid acceptor unit is conducive to anti-aggregation and thus improves the V-oc and efficiencies. Therefore, higher efficiencies were achieved for XW37 and XW39, compared with XW36 and XW38, respectively. Interestingly, although the individual XW36 dye shows a lowest efficiency among the four dyes, a highest efficiency of 11.7% was obtained for XW36 on the basis of synergetic adsorption with chenodeoxycholic acid and PT-C6 because of simultaneously improved J and Voc, which may be ascribed to the lowest dye-loading amount of XW36 among all of these porphyrin dyes, with the largest vacancy area left on the TiO2 surface available for cosensitizer PT-C6, resulting in a highest J. The high efficiency of 11.7% is one of the highest efficiencies using I-/I-3(-) electrolytes in DSSCs. These results provide an effective strategy for developing efficient DSSCs by the targeted coadsorption and cosensitization of porphyrin sensitizers optimized through introducing a bis(ortho-alkoxy)-wrapped phenyl group into the phenothiazine donor and/or methyl groups into the benzoic acid acceptor unit.

  • 79. Mao, Wenxuan
    et al.
    Zhang, Junji
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Chen
    Tian, He
    Regioisomerically pure multiaryl coronene derivatives: highly efficient synthesis via bay-extended perylene tetrabutylester2017In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 53, no 36, p. 5052-5055Article in journal (Refereed)
    Abstract [en]

    By a facile strategy, we obtained three pure regioisomers of multiaryl coronene bisimide (CBI) derivatives via IBr-mediated annelation and subsequent Suzuki coupling reactions with high yields. A series of aromatic groups with different electron properties were efficiently introduced to obtain functional CBI derivatives under mild conditions with good yields. Furthermore, the annelation mechanism as well as the optical and electrochemical properties of CBI derivatives were further investigated.

  • 80.
    Olsen, Jogvan Magnus Haugaard
    et al.
    UiT Arctic Univ Norway, Dept Chem, Hylleraas Ctr Quantum Mol Sci, N-9037 Tromso, Norway..
    Reine, Simen
    Univ Oslo, Dept Chem, Hylleraas Ctr Quantum Mol Sci, N-0315 Oslo, Norway..
    Vahtras, Olav
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Kjellgren, Erik
    Univ Southern Denmark, Dept Phys Chem & Pharm, DK-5230 Odense M, Denmark..
    Reinholdt, Peter
    Univ Southern Denmark, Dept Phys Chem & Pharm, DK-5230 Odense M, Denmark..
    Dundas, Karen Oda Hjorth
    UiT Arctic Univ Norway, Dept Chem, Hylleraas Ctr Quantum Mol Sci, N-9037 Tromso, Norway..
    Li, Xin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Cukras, Janusz
    Univ Warsaw, Dept Chem, PL-02093 Warsaw, Poland..
    Ringholm, Magnus
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. UiT Arctic Univ Norway, Dept Chem, Hylleraas Ctr Quantum Mol Sci, N-9037 Tromso, Norway..
    Hedegard, Erik D.
    Lund Univ, Div Theoret Chem, SE-22362 Lund, Sweden..
    Di Remigio, Roberto
    UiT Arctic Univ Norway, Dept Chem, Hylleraas Ctr Quantum Mol Sci, N-9037 Tromso, Norway..
    List, Nanna H.
    Stanford Univ, PULSE Inst, Stanford, CA 94305 USA.;SLAC Natl Accelerator Lab, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Chem, Stanford, CA 94305 USA.;Stanford Univ, PULSE Inst, Stanford, CA 94305 USA.;SLAC Natl Accelerator Lab, Menlo Pk, CA 94025 USA..
    Faber, Rasmus
    Tech Univ Denmark, DTU Chem, DK-2800 Lyngby, Denmark..
    Tenorio, Bruno Nunes Cabral
    Tech Univ Denmark, DTU Chem, DK-2800 Lyngby, Denmark..
    Bast, Radovan
    UiT Arctic Univ Norway, Dept Chem, Hylleraas Ctr Quantum Mol Sci, N-9037 Tromso, Norway..
    Pedersen, Thomas Bondo
    Univ Oslo, Dept Chem, Hylleraas Ctr Quantum Mol Sci, N-0315 Oslo, Norway..
    Rinkevicius, Zilvinas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. Kaunas Univ Technol, Dept Phys, Fac Math & Nat Sci, LT-51368 Kaunas, Lithuania..
    Sauer, Stephan P. A.
    Univ Copenhagen, Dept Chem, DK-2100 Copenhagen O, Denmark..
    Mikkelsen, Kurt V.
    Univ Copenhagen, Dept Chem, DK-2100 Copenhagen O, Denmark..
    Kongsted, Jacob
    Univ Southern Denmark, Dept Phys Chem & Pharm, DK-5230 Odense M, Denmark..
    Coriani, Sonia
    Tech Univ Denmark, DTU Chem, DK-2800 Lyngby, Denmark..
    Ruud, Kenneth
    UiT Arctic Univ Norway, Dept Chem, Hylleraas Ctr Quantum Mol Sci, N-9037 Tromso, Norway..
    Helgaker, Trygve
    Univ Oslo, Dept Chem, Hylleraas Ctr Quantum Mol Sci, N-0315 Oslo, Norway..
    Jensen, Hans Jorgen Aa.
    Univ Southern Denmark, Dept Phys Chem & Pharm, DK-5230 Odense M, Denmark..
    Norman, Patrick
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Dalton Project: A Python platform for molecular- and electronic-structure simulations of complex systems2020In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 152, no 21Article in journal (Refereed)
    Abstract [en]

    The Dalton Project provides a uniform platform access to the underlying full-fledged quantum chemistry codes Dalton and LSDalton as well as the PyFraME package for automatized fragmentation and parameterization of complex molecular environments. The platform is written in Python and defines a means for library communication and interaction. Intermediate data such as integrals are exposed to the platform and made accessible to the user in the form of NumPy arrays, and the resulting data are extracted, analyzed, and visualized. Complex computational protocols that may, for instance, arise due to a need for environment fragmentation and configuration-space sampling of biochemical systems are readily assisted by the platform. The platform is designed to host additional software libraries and will serve as a hub for future modular software development efforts in the distributed Dalton community.

  • 81.
    Qian, Jun
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Gharibi, Arash
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Li, Xin
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    He, Sailing
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Organically modified silica nanoparticles with photosensitizing drugs encapsulated for photodynamic therapy2008In: Optics InfoBase Conference Papers, 2008Conference paper (Refereed)
    Abstract [en]

    Organically modified silica nanoparticles, doped with photosensitizers, are synthesized, characterized and used for photodynamic therapy (PDT) of cancer. These nanoparticles were uptaken by tumor cells in vitro and the effect of photon-induced toxicity was demonstrated.

  • 82.
    Qian, Zhengliang
    et al.
    East China Univ Sci & Technol, Sch Chem & Mol Engn, Feringa Nobel Prize Scientist Joint Res Ctr, Key Lab Adv Mat, 130 Meilong Rd, Shanghai 200237, Peoples R China.;East China Univ Sci & Technol, Sch Chem & Mol Engn, Feringa Nobel Prize Scientist Joint Res Ctr, Joint Int Res Lab Precis Chem & Mol Engn, 130 Meilong Rd, Shanghai 200237, Peoples R China..
    Li, Xin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Yuan, Tao
    East China Univ Sci & Technol, Sch Chem & Mol Engn, Feringa Nobel Prize Scientist Joint Res Ctr, Key Lab Adv Mat, 130 Meilong Rd, Shanghai 200237, Peoples R China.;East China Univ Sci & Technol, Sch Chem & Mol Engn, Feringa Nobel Prize Scientist Joint Res Ctr, Joint Int Res Lab Precis Chem & Mol Engn, 130 Meilong Rd, Shanghai 200237, Peoples R China..
    Huang, Xinghua
    East China Univ Sci & Technol, Sch Chem & Mol Engn, Feringa Nobel Prize Scientist Joint Res Ctr, Key Lab Adv Mat, 130 Meilong Rd, Shanghai 200237, Peoples R China.;East China Univ Sci & Technol, Sch Chem & Mol Engn, Feringa Nobel Prize Scientist Joint Res Ctr, Joint Int Res Lab Precis Chem & Mol Engn, 130 Meilong Rd, Shanghai 200237, Peoples R China..
    Wang, Qiaochun
    East China Univ Sci & Technol, Sch Chem & Mol Engn, Feringa Nobel Prize Scientist Joint Res Ctr, Key Lab Adv Mat, 130 Meilong Rd, Shanghai 200237, Peoples R China.;East China Univ Sci & Technol, Sch Chem & Mol Engn, Feringa Nobel Prize Scientist Joint Res Ctr, Joint Int Res Lab Precis Chem & Mol Engn, 130 Meilong Rd, Shanghai 200237, Peoples R China..
    Ågren, Hans
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Tian, He
    East China Univ Sci & Technol, Sch Chem & Mol Engn, Feringa Nobel Prize Scientist Joint Res Ctr, Key Lab Adv Mat, 130 Meilong Rd, Shanghai 200237, Peoples R China.;East China Univ Sci & Technol, Sch Chem & Mol Engn, Feringa Nobel Prize Scientist Joint Res Ctr, Joint Int Res Lab Precis Chem & Mol Engn, 130 Meilong Rd, Shanghai 200237, Peoples R China..
    Divalent Pseudorotaxane with Polarized Plug-Socket and Padlock Functions2018In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 20, no 6, p. 1487-1490Article in journal (Refereed)
    Abstract [en]

    A dual-pore structured host composed of one 24-crown-8 and one 34-crown-10, and a "U"-shaped guest consisting of two different recognition units, one dibenzylammonium and one viologen, were synthesized and bound 1:1 into a divalent pseudorotaxane P1. P1 can mimic the inserting and pulling out functions of a polarized plug-socket system under solvent driven stimulus and can also realize the locking and unlocking actions of a padlock under pH stimulus.

  • 83.
    Rinkevicius, Zilvinas
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Rosal Sandberg, Jaime Axel
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Mikkelsen, Kurt V.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    A Hybrid Density Functional Theory/Molecular Mechanics Approach for Linear Response Properties in Heterogeneous Environments2014In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 10, no 3, p. 989-1003Article in journal (Refereed)
    Abstract [en]

    We introduce a density functional theory/molecular mechanical approach for computation of linear response properties of molecules in heterogeneous environments, such as metal surfaces or nanoparticles embedded in solvents. The heterogeneous embedding environment, consisting from metallic and nonmetallic parts, is described by combined force fields, where conventional force fields are used for the nonmetallic part and capacitance-polarization-based force fields are used for the metallic part. The presented approach enables studies of properties and spectra of systems embedded in or placed at arbitrary shaped metallic surfaces, clusters, or nanoparticles. The capability and performance of the proposed approach is illustrated by sample calculations of optical absorption spectra of thymidine absorbed on gold surfaces in an aqueous environment, where we study how different organizations of the gold surface and how the combined, nonadditive effect of the two environments is reflected in the optical absorption spectrum.

  • 84.
    Rinkevicius, Zilvinas
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Li, Xin
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for High Performance Computing, PDC.
    Vahtras, Olav
    KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Ahmadzadeh, Karan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Brand, Manuel
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Ringholm, Magnus
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    List, N. H.
    Scheurer, M.
    Scott, M.
    Dreuw, A.
    Norman, Patrick
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    VeloxChem: A Python-driven density-functional theory program for spectroscopy simulations in high-performance computing environments2019In: Wiley Interdisciplinary Reviews. Computational Molecular Science, ISSN 1759-0876, E-ISSN 1759-0884, article id e1457Article in journal (Refereed)
    Abstract [en]

    An open-source program named VeloxChem has been developed for the calculation of electronic real and complex linear response functions at the levels of Hartree–Fock and Kohn–Sham density functional theories. With an object-oriented program structure written in a Python/C++ layered fashion, VeloxChem enables time-efficient prototyping of novel scientific approaches without sacrificing computational efficiency, so that molecular systems involving up to and beyond 500 second-row atoms (or some 10,000 contracted and in part diffuse Gaussian basis functions) can be routinely addressed. In addition, VeloxChem is equipped with a polarizable embedding scheme for the treatment of the classical electrostatic interactions with an environment that in turn is modeled by atomic site charges and polarizabilities. The underlying hybrid message passing interface (MPI)/open multiprocessing (OpenMP) parallelization scheme makes VeloxChem suitable for execution in high-performance computing cluster environments, showing even slightly beyond linear scaling for the Fock matrix construction with use of up to 16,384 central processing unit (CPU) cores. An efficient—with respect to convergence rate and overall computational cost—multifrequency/gradient complex linear response equation solver enables calculations not only of conventional spectra, such as visible/ultraviolet/X-ray electronic absorption and circular dichroism spectra, but also time-resolved linear response signals as due to ultra-short weak laser pulses. VeloxChem distributed under the GNU Lesser General Public License version 2.1 (LGPLv2.1) license and made available for download from the homepage https://veloxchem.org. This article is categorized under: Software > Quantum Chemistry Electronic Structure Theory > Density Functional Theory Theoretical and Physical Chemistry > Spectroscopy.

  • 85.
    Rinkevicius, Zilvinas
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Sandberg, Jaime A. R.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Linares, Mathieu
    Norman, Patrick
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hybrid Complex Polarization Propagator/Molecular Mechanics Method for Heterogeneous Environments2016In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 12, no 6, p. 2661-2667Article in journal (Refereed)
    Abstract [en]

    We introduce a hybrid complex polarization propagator/molecular mechanics method for the calculation of near-resonant and resonant response properties of molecules in heterogeneous environments, which consist of a metallic surface, or nanoparticle, and a solvent. The applicability and performance of the method is demonstrated by computations of linear absorption spectra of p-nitroaniline physisorbed at a gold/dimethyl sulfoxide interface in the UV/vis and near carbon-K-edge regions of the spectrum. It is shown that the shift of absorption cross-section induced by the heterogeneous environment varies significantly depending on the nature,of the excited states encountered in the targeted frequency region as' well as on the actual size of the resonant frequencies, and that the solvent component of the heterogeneous environment is responsible for the major part of the environmental shift, especially in the higher frequency range of the carbon K-edge region.

  • 86.
    Rinkevicius, Zilvinas
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Xin, Li
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Vahtras, Olav
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Brand, Manuel
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Ahmadzadeh, Karan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Ringholm, Magnus
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. UiT, Dept Chem, Tromso, Norway..
    List, Nanna
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Norman, Patrick
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    New and efficient Python/C plus plus modular library for real and complex response functions at the level of Kohn-Sham density functional theory2019In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 257Article in journal (Other academic)
  • 87. Seritan, S.
    et al.
    Bannwarth, C.
    Fales, B. S.
    Hohenstein, E. G.
    Isborn, C. M.
    Kokkila-Schumacher, S. I. L.
    Li, Xin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Liu, F.
    Luehr, N.
    Snyder, J.W., Jr.
    Song, C.
    Titov, A. V.
    Ufimtsev, I. S.
    Wang, L. -P
    Martínez, T. J.
    TeraChem: A graphical processing unit-accelerated electronic structure package for large-scale ab initio molecular dynamics2020In: Wiley Interdisciplinary Reviews. Computational Molecular Science, ISSN 1759-0876, E-ISSN 1759-0884Article in journal (Refereed)
    Abstract [en]

    TeraChem was born in 2008 with the goal of providing fast on-the-fly electronic structure calculations to facilitate ab initio molecular dynamics studies of large biochemical systems such as photoswitchable proteins and multichromophoric antenna complexes. Originally developed for videogaming applications, graphics processing units (GPUs) offered a low-cost parallel computer architecture that became more accessible for general-purpose GPU computing with the release of CUDA in 2007. The evaluation of the electron repulsion integrals (ERIs) is a major bottleneck in electronic structure codes and provides an attractive target for acceleration on GPUs. Thus, highly efficient routines for evaluation of and contractions between the ERIs and density matrices were implemented in TeraChem. Electronic structure methods were developed and implemented to leverage these integral contraction routines, resulting in the first quantum chemistry package designed from the ground up for GPUs. This GPU acceleration makes TeraChem capable of performing large-scale ground and excited state calculations in the gas and condensed phase. Today, TeraChem's speed forms the basis for a suite of quantum chemistry applications, including optimization and dynamics of proteins, automated and interactive chemical discovery tools, and large-scale nonadiabatic dynamics simulations. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods Software > Quantum Chemistry Structure and Mechanism > Computational Biochemistry and Biophysics.

  • 88. Shen, Zhongjin
    et al.
    Chen, Jue
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Xing
    Zhou, Ying
    Yu, Ying
    Ding, Haoran
    Li, Jing
    Zhu, Linyong
    Hua, Jianli
    Synthesis and Photovoltaic Properties of Powerful Electron-Donating Indeno[1, 2-b]thiophene-Based Green D-A-pi-A Sensitizers for Dye-Sensitized Solar Cells2016In: ACS Sustainable Chemistry and Engineering, E-ISSN 2168-0485, Vol. 4, no 6, p. 3518-3525Article in journal (Refereed)
    Abstract [en]

    Three new near-infrared D-A-pi-A dyes (Si, S2, and S3) with 80 indeno[1,2-b]thiophene-based strong donor, containing 5,6-difluorobenzo[c][1,2,5]thiadiazole (DFBT), benzo[c][1,2,5]thiadiazole (BT), and 2,3diphenylpyrido[3,4-b]pyrazine (PP) as the auxiliary acceptor, respectively, were synthesized for the application of dye-sensitized solar cells. Introduction of powerful electron-donating unit of indeno[1,2-b]thiophene and the strong electron-withdrawing DFBT, BT, and PP groups into the conjugation bridge can enhance the absorption wavelength range into NIR region, where the maximum absorptions of the three compounds are all over 610 nm and S3 can reach 628 nm. Moreover, it is rare to see that the colors of the dyes are all green both in dichloromethane and on the TiO2 film. Via fine-tuning of the auxiliary moiety, the onset of incident-photon-conversion efficiency of S1-S3 can reach 850 nm and S3-based DSSCs in the presence of iodine and cobalt electrolytes show the best overall solar energy conversion efficiency of 6.29% and 7.23% under full sunlight (AM 1.5G, 100 mW cm(-2)) irradiation, which are relatively high values in organic NIR green dye-based DSSCs. Electrochemical impedance spectroscopy indicates that S3-based DSSCs can suppress charge recombination more efficiently, accounting for its higher open circuit voltage and short circuit current.

  • 89. Shi, Leilei
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhou, Min
    Muhammad, Faheem
    Ding, Yubin
    Wei, Hui
    An arylboronate locked fluorescent probe for hypochlorite2017In: The Analyst, ISSN 0003-2654, E-ISSN 1364-5528, Vol. 142, no 12, p. 2104-2108Article in journal (Refereed)
    Abstract [en]

    An unusual arylboronate based fluorescent probe R1 was synthesized for the selective and sensitive detection of ClO-. A detailed mechanistic study revealed that R1 reacted with ClO- through an oxidation to chlorination mechanism, and the arylboronate moiety in R1 acted as a "lock" to eliminate the effects of pH fluctuations. With this design strategy, R1 was successfully used to detect as low as 6.4 nM of ClO- over other ROS species in a wide pH range from 4.5 to 9.0.

  • 90. Shi, Shengwei
    et al.
    Sun, Zhengyi
    Bedoya-Pinto, Amilcar
    Graziosi, Patrizio
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Liu, Xianjie
    Hueso, Luis
    Dediu, Valentin A.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fahlman, Mats
    Hybrid Interface States and Spin Polarization at Ferromagnetic Metal-Organic Heterojunctions: Interface Engineering for Efficient Spin Injection in Organic Spintronics2014In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 24, no 30, p. 4812-4821Article in journal (Refereed)
    Abstract [en]

    Ferromagnetic metal-organic semiconductor (FM-OSC) hybrid interfaces have been shown to play an important role for spin injection in organic spintronics. Here, 11,11,12,12-tetracyanonaptho-2,6-quinodimethane (TNAP) is introduced as an interfacial layer in Co-OSCs heterojunctions with an aim to tune the spin injection. The Co/TNAP interface is investigated by use of X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS), near edge X-ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD). Hybrid interface states (HIS) are observed at Co/TNAP interfaces, resulting from chemical interactions between Co and TNAP. The energy level alignment at the Co/TNAP/OSCs interface is also obtained, and a reduction of the hole injection barrier is demonstrated. XMCD results confirm sizeable spin polarization at the Co/TNAP hybrid interface.

  • 91. Song, Heli
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Xie, Yongshu
    Branched and linear alkoxy chains-wrapped push-pull porphyrins for developing efficient dye-sensitized solar cells2017In: Dyes and pigments, ISSN 0143-7208, E-ISSN 1873-3743, Vol. 137, p. 421-429Article in journal (Refereed)
    Abstract [en]

    Four alkoxy-wrapped push-pull porphyrin dyes containing the phenothiazine derived donor and the ethynylbenzoic acid acceptor have been designed, synthesized and used as sensitizers for fabricating efficient dye-sensitized solar cells (DSSCs). Branched or linear alkoxy chains were introduced to the ortho-positions of the meso-phenyl moieties to suppress the dye aggregation and charge recombination. The effect of alkoxy chains were investigated in the absence and presence of an additional electron withdrawing benzothiadiazole unit. In the former cases, almost identical photovoltaic efficiencies of similar to 8.3% were achieved for both the branched and the linear alkoxy chains, while in the latter cases, the planar benzothiadiazole unit induces serious dye aggregation and charge recombination, resulting in lower efficiencies of 6.46% and 7.50% for the linear and branched chains, respectively, even though broader absorption was achieved. The relatively higher efficiency achieved for the dyes with branched chains may be related to the better effect of suppressing the dye aggregation and charge recombination. Furthermore, the coadsorption approach was employed, and a highest efficiency of 9.62% was achieved for the dye that features branched chains and the benzothiadiazole unit. These results compose a novel approach for developing efficient DSSCs by combining the coadsorbent with a porphyrin dye containing both the additional benzothiadiazole acceptor and branched alkoxy chains.

  • 92. Song, X.
    et al.
    Zhang, W.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Jiang, H.
    Shen, C.
    Zhu, W. -H
    Influence of ethynyl position on benzothiadiazole based D-A-π-A dye-sensitized solar cells: Spectral response and photovoltage performance2016In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 4, no 39, p. 9203-9211Article in journal (Refereed)
    Abstract [en]

    The ethynyl group has been widely employed in dye-sensitized solar cells (DSSCs) as an efficient π-spacer to prolong conjugation and promote electronic coupling at the interface of TiO2 films. However, systematic studies of the ethynyl position on metal-free organic sensitizers remain relatively rare. Herein we report indoline-based organic dyes bearing an ethynyl group at different positions of D-A-π-A organic dyes. Based on the reference dye D1, we inserted an ethynyl unit in either the left or right side of benzothiadiazole to construct two novel dyes D2 and D3. It was found that inserting an ethynyl unit to the side of the anchoring group obtained a higher molar extinction coefficient with a red shift in the absorption band. Interestingly, D2 and D3 displayed a better photovoltaic performance with respect to D1. In particular, D3 exhibits an over 90 mV enhanced open-circuit voltage (VOC) than D2 owing to a longer electron lifetime and slower charge recombination. With this incredible increase of VOC, D3 bestows a high efficiency of 7.13% with respect to D1 and D2. Coadsorption strategies are exploited for further improving the cell behaviour. As a result, cosensitization with a long-wavelength-responsive dye WS-2 was demonstrated to efficiently compensate the light-harvesting, achieving an excellent efficiency of 9.83% in the iodine electrolyte. This work has paved a useful and practical way for molecular engineering in D-A-π-A metal-free organic dyes.

  • 93.
    Sun, Lu
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hede, Thomas
    Stockholm University.
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Leck, Caroline
    Stockholm University.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Molecular Dynamics Simulations Reveal the Assembly Mechanism of Polysaccharides in Marine Aerosols2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 47, p. 25935-25941Article in journal (Other academic)
    Abstract [en]

    The high Arctic marine environment has recently detected polymer gels in atmospheric aerosol particles and cloud water originating from the surface microlayer of the open leads within the pack ice area. These polysaccharide molecules are water insoluble but water solvated, highly surface-active and highly hydrated (99% water). In order to add to the understanding and to complement missing laboratory characterization of marine polymer gels we have in this work performed an atomistic study of the assembly process and interfacial properties of polysaccharides. Our study reveals a number of salient features of the microscopic process behind polysaccharide assembly into nanogels. With three- and four-repeating units the polysaccharides assemble into a cluster in 50 ns. The aggregates grow quicker by absorbing one or two polymers each time, depending on the unit length and the type of inter-bridging cation. Although both the hydrophobic and hydrophilic domains are contracted, the latter dominates distinctly upon the contraction of solvent accessible surface areas. The establishment of inter-chain hydrogen-bonds is the key to the assembly while ionic bridges can further promote aggregation. During the assembly of the more bent four-unit polymers, intra-chain hydrogen bonds are significantly diminished by Ca2+. Meanwhile, the percentage of Ca2+ acting as an ionic bridge is more eminent, highlighting the significance of Ca2+ ions for longer-chain polysaccharides. The aggregates are able to enhance surface tension more in the presence of Ca2+ than in the presence of Na+ owing to their more compact structure. These conclusions all demonstrate that studies of the present kind provide insight into the self-assembly process and interfacial properties of marine gels. We hope this understanding will keep up the interest in the complex and the fascinating relationship between marine microbiology, atmospheric aerosols, clouds and climate.

  • 94.
    Sun, Lu
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Origin of Ion Selectivity at the Air/Water Interface2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 6, p. 4311-4318Article in journal (Refereed)
    Abstract [en]

    Among many characteristics of ions, their capability to accumulate at air/water interfaces is a particular issue that has been the subject of much research attention. For example, the accumulation of halide anions (Cl-, Br-, I-) at the water surface is of great importance to heterogeneous reactions that are of environmental concern. However, the actual mechanism that drives anions towards the air/water interface remains unclear. In this work, we have performed atomistic simulations using polarizable models to mimic ionic behavior under atmospheric conditions. We find that larger anions are abundant at the water surface and that the cations are pulled closer to the surface by the counterions. We propose that polarization effects stabilize the anions with large radii when approaching the surface. This energetically more favorable situation is caused by the fact that the more polarized anions at the surface attract water molecules more strongly. Of relevance is also the ordering of the surface water molecules with their hydrogen atoms pointing outwards which induce an external electronic field that leads to a different surface behavior of anions and cations. The water-water interaction is weakened by the distinct water-ion attraction, a point contradicting the proposition that F- is a kosmotrope. The simulation results thus allow us to obtain a more holistic understanding of the interfacial properties of ionic solutions and atmospheric aerosols.

  • 95. Sun, Xi
    et al.
    Wang, Yueqiang
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhu, Weihong
    Tian, He
    Xie, Yongshu
    Cosensitizers for simultaneous filling up of both absorption valleys of porphyrins: a novel approach for developing efficient panchromatic dye-sensitized solar cells2014In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 50, no 98, p. 15609-15612Article in journal (Refereed)
    Abstract [en]

    XS1-XS3 have been synthesized by introducing an auxiliary acceptor into D-pi-A dyes for simultaneous filling up of both absorption valleys of porphyrin dyes at around 550 and 380 nm. Thus, panchromatic DSSCs with the highest efficiency of 10.75% were achieved by cosensitization. This work provides a strategy for designing cosensitizers for porphyrin dyes.

  • 96. Tang, Y.
    et al.
    Ding, Y.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, T.
    Zhang, W.
    Xie, Y.
    Acylation of dipyrromethanes at the α and β positions and further development of fluorescent Zn2+ probes2014In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 206, p. 291-302Article in journal (Refereed)
    Abstract [en]

    The acylation of 5-aryl dipyrromethanes afforded products with interestingly rich substitution modes, i.e.; α- and β-monoacylated (modes a and b), and α, α′-, α, β′- and β, β′-diacylated (modes c-e). Especially, the β- and β, β′-acylation modes are unprecedented. And most of these products can be synthesized at a gram scale. The anisoyl substituted 5-(4-cyanophenyl) dipyrromethanes (1a-1e) were oxidized with DDQ. Thus, 1a and 1b afforded the corresponding dipyrrins 1a-DPR, and 1b-DPR. More interestingly, the diacylated ones 1c-1e could not be oxidized by DDQ. Instead, 1c-OH-1e-OH were obtained with a hydroxyl group attached to the 5-position. 1a-DPR-1e-OH were further developed as fluorescence turn-on Zn2+ probes. 1d-OH showed the highest sensitivity, with a detection limit of 1.5 × 10-8 M, and it was successfully applied in Zn2+ imaging in Hela cells. Furthermore, single crystals of two Zn2+ complexes were obtained and analyzed by X-ray diffraction.

  • 97.
    Tang, Yunyu
    et al.
    Laboratory of Quality Safety and Processing for Aquatic Product, East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai 200090, China.
    Liu, X.
    Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, China.
    Wang, Y.
    Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, China.
    Liu, Qingyun
    College of Chemical and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266590, China.
    Li, Xin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Li, Chengjie
    Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, China.
    Shen, Xiaosheng
    Laboratory of Quality Safety and Processing for Aquatic Product, East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai 200090, China.
    Xie, Y.
    Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, China.
    Solar cells sensitized by porphyrin dyes containing a substituted carbazole donor with synergistically extended absorption and suppressed the dye aggregation2020In: Chinese Chemical Letters, ISSN 1001-8417, E-ISSN 1878-5964, Vol. 31, no 7, p. 1927-1930Article in journal (Refereed)
    Abstract [en]

    To achieve high power conversion efficiencies (PCEs), three porphyrin sensitizers have been synthesized and explored to simultaneously enhance the photocurrent (Jsc) and photovoltage (Voc). On basis of the XW4, a benzothiadiazole (BTD) unit has been introduced to afford XW57 with the aim to extend the absorption wavelength and enhance the light harvesting ability. As a result, a Jsc of 13.72 mA/cm2 has been obtained for XW57, higher than that of XW4. On this basis, XW58 has been prepared by modifying the carbazole-based donor with two bulky dihexyloxyphenyl groups, and the superior anti-aggregation character raises the Voc from 781 mV (XW4) to 844 mV. When both the BTD unit and the bulky groups are introduced to the acceptor and donor units, respectively, the resulting sensitizer XW59 exhibits a highest PCE value of 7.34% with synergistically enhanced Jsc of 13.19 mA/cm2 and Voc of 793 mV. These results provide further insight into developing high performance dye-sensitized solar cells

  • 98. Tang, Yunyu
    et al.
    Wang, Yueqiang
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhu, Wei-Hong
    Xie, Yongshu
    Porphyrins Containing a Triphenylamine Donor and up to Eight Alkoxy Chains for Dye-Sensitized Solar Cells: A High Efficiency of 10.9%2015In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 50, p. 27976-27985Article in journal (Refereed)
    Abstract [en]

    Porphyrins are promising DSSC sensitizers due to their structural similarity to chlorophylls as well as their tunable strong absorption. Herein, a novel D-pi-A porphyrin dye XW14 containing a strongly electron-donating triphenyl-amine moiety as the electron donor was designed and synthesized: To avoid undesirably decreased V-oc caused by dye aggregation effect, two methoxy or hexyloxy chains were introduced to the para positions of the triphenylamine moiety to afford XW15 and XW16, respectively. To further extend the absorption to a longer wavelength, a benzothiadiazole unit was introduced as an auxiliary acceptor to furnish XW17. Compared with XW14, the introduction of additional methoxy or hexyloxy groups in XW15 and XW16 red-shift the onset wavelengths from 760 to 780 and 790 nm, respectively. More impressively, XW17 has a more extended pi-conjugation framework, and thus, it exhibits a much broader IPCE spectrum with an extremely red-shifted onset wavelength Of 830 mu, resulting in the highest J(sc) (18.79 mA cm(-2)). On the other hand, the hexyloxy chains are favorable for suppressing the dye aggregation effect, and thus XW16 shows the highest V-oc 734 mV. As a result, XW16 and XW17 demonstrate photovoltaic efficiencies of 9,1 and 9.5%, respectively, higher than those of XW14 (8.6%) and XW15 (8.7%), and obviously higher than that of 7.94% for our previously reported dye, XW4. On the basis of optimized porphyrin dye XW17, we used a nonporphyrin dye with a high V-oc and strong absorption around 500 inn (WS-5) as the cosensitizer to improve the V-oc from 700 to 748 mV, with synergistical J(sc) enhancement from 18.79 to 20.30 mA cm(-2). Thus, the efficiency was dramatically enhanced to 10.9%, which is among the highest efficiencies obtained for the DSSCs based on traditional iodine electrolyte. In addition, the DSSCs based on XW17 + WS-5 exhibit good photostability, which is beneficial for practical applications.

  • 99. Tian, Guojian
    et al.
    Cai, Shengyun
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wang, Qiaochun
    Huang, Jinhai
    Su, Jianhua
    A new D-A-pi-A type organic sensitizer based on substituted dihydroindolo [2,3-b] carbazole and DPP unit with a bulky branched alkyl chain for highly efficient DSCs2015In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 7, p. 3777-3784Article in journal (Refereed)
    Abstract [en]

    Two new D-A-pi-A configuration metal-free organic sensitizers (T1-T2) based on 5,7-dihexyl-6,12-diphenyl-5,7-dihydroindolo[2,3-b]carbazole and a DPP unit with a bulky branched alkyl chain have been synthesized for dye-sensitized solar cells. Due to a bulky branched alkyl chain being attached to the donor and DPP unit, both compounds obtain high V-oc values. Under standard global AM 1.5 solar light conditions, the T1 based-device gives a high conversion efficiency of 8.24% with a J(sc) of 15.72 mA cm(-2), a V-oc of 0.74 V and a FF of 0.71. These excellent performances make the donor dihydroindolo[2,3-b] carbazole and DPP unit promising candidates for further application in DSCs.

  • 100. Wang, J.
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhang, J.
    Tian, H.
    Modulating a D-Π-A type diarylethene for on-demand Cu2+ check via photo-switchable detection range and sensitivity2018In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 257, p. 77-86Article in journal (Refereed)
    Abstract [en]

    Detection range and sensitivity are two important parameters in a sensing system. Unfortunately, in common sensory systems, wide detection range always suffers from low sensitivity and vice versa. Thus, it becomes more and more desirable to design sensors with both wide detection range and high sensitivity. Here, we report a sensory system based on a photo-switchable D-π-A type diarylethene (SDE), which presents both wide detection range and high sensitivity under alternate light modulation. The D-π-A structure endows the sensor with high energy level of HOMO, which enabled the oxidation of both photoisomer SDEo/SDEc by Cu2+. While the discrepancy in energy levels of oxidation potentials in SDE photoisomers leads to their different reactivity, or in another word, sensitivity towards Cu2+. The inherent oxidative cycloreversion of SDEc to SDEo, on the other hand, provides a possibility that two photoisomers would detect Cu2+ in different working concentrations. The open form was employed for the detection of Cu2+ in a wider concentration range (0–13.0 equivalent) with relatively lower sensitivity (6.4 × 10−7 M). While the closed form was able to probe Cu2+ in lower concentration (0–3.0 equivalent) with higher sensitivity (6.6 × 10−9 M). Based on this photo-switchable sensing activity, a molecular multimeter of variable detection range for Cu2+ was then constructed.

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