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  1. Article: Benchmarking coarse-grained models of organic semiconductors via deep backmapping.

    Stieffenhofer, Marc / Scherer, Christoph / May, Falk / Bereau, Tristan / Andrienko, Denis

    Frontiers in chemistry

    2022  Volume 10, Page(s) 982757

    Abstract: The potential of mean force is an effective coarse-grained potential, which is often approximated by pairwise potentials. While the approximated potential reproduces certain distributions of the reference all-atom model with remarkable accuracy, ... ...

    Abstract The potential of mean force is an effective coarse-grained potential, which is often approximated by pairwise potentials. While the approximated potential reproduces certain distributions of the reference all-atom model with remarkable accuracy, important cross-correlations are typically not captured. In general, the quality of coarse-grained models is evaluated at the coarse-grained resolution, hindering the detection of important discrepancies between the all-atom and coarse-grained ensembles. In this work, the quality of different coarse-grained models is assessed at the atomistic resolution deploying reverse-mapping strategies. In particular, coarse-grained structures for Tris-Meta-Biphenyl-Triazine are reverse-mapped from two different sources: 1) All-atom configurations projected onto the coarse-grained resolution and 2) snapshots obtained by molecular dynamics simulations based on the coarse-grained force fields. To assess the quality of the coarse-grained models, reverse-mapped structures of both sources are compared revealing significant discrepancies between the all-atom and the coarse-grained ensembles. Specifically, the reintroduced details enable force computations based on the all-atom force field that yield a clear ranking for the quality of the different coarse-grained models.
    Language English
    Publishing date 2022-09-09
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2711776-5
    ISSN 2296-2646
    ISSN 2296-2646
    DOI 10.3389/fchem.2022.982757
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article: Conductance Switching in Liquid Crystal-Inspired Self-Assembled Monolayer Junctions

    Dlugosch, Julian M. / Seim, Henning / Bora, Achyut / Kamiyama, Takuya / Lieberman, Itai / May, Falk / Müller-Plathe, Florian / Nefedov, Alexei / Prasad, Saurav / Resch, Sebastian / Saller, Kai / Seim, Christian / Speckbacher, Maximilian / Voges, Frank / Tornow, Marc / Kirsch, Peer

    ACS applied materials & interfaces. 2022 July 01, v. 14, no. 27

    2022  

    Abstract: We present the prototype of a ferroelectric tunnel junction (FTJ), which is based on a self-assembled monolayer (SAM) of small, functional molecules. These molecules have a structure similar to those of liquid crystals, and they are embedded between two ... ...

    Abstract We present the prototype of a ferroelectric tunnel junction (FTJ), which is based on a self-assembled monolayer (SAM) of small, functional molecules. These molecules have a structure similar to those of liquid crystals, and they are embedded between two solid-state electrodes. The SAM, which is deposited through a short sequence of simple fabrication steps, is extremely thin (3.4 ± 0.5 nm) and highly uniform. The functionality of the FTJ is ingrained in the chemical structure of the SAM components: a conformationally flexible dipole that can be reversibly reoriented in an electrical field. Thus, the SAM acts as an electrically switchable tunnel barrier. Fabricated stacks of Al/Al₂O₃/SAM/Pb/Ag with such a polar SAM show pronounced hysteretic, reversible conductance switching at voltages in the range of ±2–3 V, with a conductance ratio of the low and the high resistive states of up to 100. The switching mechanism is analyzed using a combination of quantum chemical, molecular dynamics, and tunneling resistance calculation methods. In contrast to more common, inorganic material-based FTJs, our approach using SAMs of small organic molecules allows for a high degree of functional complexity and diversity to be integrated by synthetic standard methods, while keeping the actual device fabrication process robust and simple. We expect that this technology can be further developed toward a level that would then allow its application in the field of information storage and processing, in particular for in-memory and neuromorphic computing architectures.
    Keywords chemical structure ; electric field ; information storage ; molecular dynamics ; prototypes ; quantum mechanics
    Language English
    Dates of publication 2022-0701
    Size p. 31044-31053.
    Publishing place American Chemical Society
    Document type Article
    ISSN 1944-8252
    DOI 10.1021/acsami.2c05264
    Database NAL-Catalogue (AGRICOLA)

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  3. Article ; Online: Unicolored phosphor-sensitized fluorescence for efficient and stable blue OLEDs.

    Heimel, Paul / Mondal, Anirban / May, Falk / Kowalsky, Wolfgang / Lennartz, Christian / Andrienko, Denis / Lovrincic, Robert

    Nature communications

    2018  Volume 9, Issue 1, Page(s) 4990

    Abstract: Improving lifetimes and efficiencies of blue organic light-emitting diodes is clearly a scientific challenge. Towards solving this challenge, we propose a unicolored phosphor-sensitized fluorescence approach, with phosphorescent and fluorescent emitters ... ...

    Abstract Improving lifetimes and efficiencies of blue organic light-emitting diodes is clearly a scientific challenge. Towards solving this challenge, we propose a unicolored phosphor-sensitized fluorescence approach, with phosphorescent and fluorescent emitters tailored to preserve the initial color of phosphorescence. Using this approach, we design an efficient sky-blue light-emitting diode with radiative decay times in the submicrosecond regime. By changing the concentration of fluorescent emitter, we show that the lifetime is proportional to the reduction of the radiative decay time and tune the operational stability to lifetimes of up to 320 h (80% decay, initial luminance of 1000 cd/m
    Language English
    Publishing date 2018-11-26
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 2553671-0
    ISSN 2041-1723 ; 2041-1723
    ISSN (online) 2041-1723
    ISSN 2041-1723
    DOI 10.1038/s41467-018-07432-2
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article ; Online: Conductance Switching in Liquid Crystal-Inspired Self-Assembled Monolayer Junctions.

    Dlugosch, Julian M / Seim, Henning / Bora, Achyut / Kamiyama, Takuya / Lieberman, Itai / May, Falk / Müller-Plathe, Florian / Nefedov, Alexei / Prasad, Saurav / Resch, Sebastian / Saller, Kai / Seim, Christian / Speckbacher, Maximilian / Voges, Frank / Tornow, Marc / Kirsch, Peer

    ACS applied materials & interfaces

    2022  Volume 14, Issue 27, Page(s) 31044–31053

    Abstract: We present the prototype of a ferroelectric tunnel junction (FTJ), which is based on a self-assembled monolayer (SAM) of small, functional molecules. These molecules have a structure similar to those of liquid crystals, and they are embedded between two ... ...

    Abstract We present the prototype of a ferroelectric tunnel junction (FTJ), which is based on a self-assembled monolayer (SAM) of small, functional molecules. These molecules have a structure similar to those of liquid crystals, and they are embedded between two solid-state electrodes. The SAM, which is deposited through a short sequence of simple fabrication steps, is extremely thin (3.4 ± 0.5 nm) and highly uniform. The functionality of the FTJ is ingrained in the chemical structure of the SAM components: a conformationally flexible dipole that can be reversibly reoriented in an electrical field. Thus, the SAM acts as an electrically switchable tunnel barrier. Fabricated stacks of Al/Al
    Language English
    Publishing date 2022-07-01
    Publishing country United States
    Document type Journal Article
    ISSN 1944-8252
    ISSN (online) 1944-8252
    DOI 10.1021/acsami.2c05264
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article ; Online: Can lattice models predict the density of states of amorphous organic semiconductors?

    May, Falk / Baumeier, Björn / Lennartz, Christian / Andrienko, Denis

    Physical review letters

    2012  Volume 109, Issue 13, Page(s) 136401

    Abstract: We extend existing lattice models of small-molecule amorphous semiconductors by accounting for changes in molecular polarizability upon charging or excitation. A compact expression of this contribution to the density of states is provided. Although the ... ...

    Abstract We extend existing lattice models of small-molecule amorphous semiconductors by accounting for changes in molecular polarizability upon charging or excitation. A compact expression of this contribution to the density of states is provided. Although the lattice model and the description based on a microscopic morphology both qualitatively predict an additional broadening, shift, and an exponential tail (traps) of the density of states, a quantitative agreement between the two cannot be achieved.
    Language English
    Publishing date 2012-09-28
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.109.136401
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  6. Article ; Online: Interaction of spin and vibrations in transport through single-molecule magnets.

    May, Falk / Wegewijs, Maarten R / Hofstetter, Walter

    Beilstein journal of nanotechnology

    2011  Volume 2, Page(s) 693–698

    Abstract: We study electron transport through a single-molecule magnet (SMM) and the interplay of its anisotropic spin with quantized vibrational distortions of the molecule. Based on numerical renormalization group calculations we show that, despite the ... ...

    Abstract We study electron transport through a single-molecule magnet (SMM) and the interplay of its anisotropic spin with quantized vibrational distortions of the molecule. Based on numerical renormalization group calculations we show that, despite the longitudinal anisotropy barrier and small transverse anisotropy, vibrational fluctuations can induce quantum spin-tunneling (QST) and a QST-Kondo effect. The interplay of spin scattering, QST and molecular vibrations can strongly enhance the Kondo effect and induce an anomalous magnetic field dependence of vibrational Kondo side-bands.
    Language English
    Publishing date 2011-10-18
    Publishing country Germany
    Document type Journal Article
    ZDB-ID 2583584-1
    ISSN 2190-4286 ; 2190-4286
    ISSN (online) 2190-4286
    ISSN 2190-4286
    DOI 10.3762/bjnano.2.75
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  7. Article: Design Rules for Charge-Transport Efficient Host Materials for Phosphorescent Organic Light-Emitting Diodes

    May, Falk / Al-Helwi Mustapha / Andrienko Denis / Baumeier Björn / Fuchs Evelyn / Kowalsky Wolfgang / Lennartz Christian

    Journal of the American Chemical Society. 2012 Aug. 22, v. 134, no. 33

    2012  

    Abstract: The use of blue phosphorescent emitters in organic light-emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies, the alignment of levels with respect to the emitter, the ability to form and ... ...

    Abstract The use of blue phosphorescent emitters in organic light-emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies, the alignment of levels with respect to the emitter, the ability to form and sustain amorphous order, material processability, and an adequate charge carrier mobility. A possible design strategy is to choose a π-conjugated core with a high triplet level and to fulfill the other requirements by using suitable substituents. Bulky substituents, however, induce large spatial separations between conjugated cores, can substantially reduce intermolecular electronic couplings, and decrease the charge mobility of the host. In this work we analyze charge transport in amorphous 2,8-bis(triphenylsilyl)dibenzofuran, an electron-transporting material synthesized to serve as a host in deep-blue OLEDs. We show that mesomeric effects delocalize the frontier orbitals over the substituents recovering strong electronic couplings and lowering reorganization energies, especially for electrons, while keeping energetic disorder small. Admittance spectroscopy measurements reveal that the material has indeed a high electron mobility and a small Poole–Frenkel slope, supporting our conclusions. By linking electronic structure, molecular packing, and mobility, we provide a pathway to the rational design of hosts with high charge mobilities.
    Keywords dibenzofuran ; electrons ; hosts ; phosphorescence ; spectroscopy
    Language English
    Dates of publication 2012-0822
    Size p. 13818-13822.
    Publishing place American Chemical Society
    Document type Article
    ZDB-ID 3155-0
    ISSN 1520-5126 ; 0002-7863
    ISSN (online) 1520-5126
    ISSN 0002-7863
    DOI 10.1021%2Fja305310r
    Database NAL-Catalogue (AGRICOLA)

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  8. Article ; Online: Design rules for charge-transport efficient host materials for phosphorescent organic light-emitting diodes.

    May, Falk / Al-Helwi, Mustapha / Baumeier, Björn / Kowalsky, Wolfgang / Fuchs, Evelyn / Lennartz, Christian / Andrienko, Denis

    Journal of the American Chemical Society

    2012  Volume 134, Issue 33, Page(s) 13818–13822

    Abstract: The use of blue phosphorescent emitters in organic light-emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies, the alignment of levels with respect to the emitter, the ability to form and ... ...

    Abstract The use of blue phosphorescent emitters in organic light-emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies, the alignment of levels with respect to the emitter, the ability to form and sustain amorphous order, material processability, and an adequate charge carrier mobility. A possible design strategy is to choose a π-conjugated core with a high triplet level and to fulfill the other requirements by using suitable substituents. Bulky substituents, however, induce large spatial separations between conjugated cores, can substantially reduce intermolecular electronic couplings, and decrease the charge mobility of the host. In this work we analyze charge transport in amorphous 2,8-bis(triphenylsilyl)dibenzofuran, an electron-transporting material synthesized to serve as a host in deep-blue OLEDs. We show that mesomeric effects delocalize the frontier orbitals over the substituents recovering strong electronic couplings and lowering reorganization energies, especially for electrons, while keeping energetic disorder small. Admittance spectroscopy measurements reveal that the material has indeed a high electron mobility and a small Poole-Frenkel slope, supporting our conclusions. By linking electronic structure, molecular packing, and mobility, we provide a pathway to the rational design of hosts with high charge mobilities.
    Language English
    Publishing date 2012-08-22
    Publishing country United States
    Document type Journal Article
    ZDB-ID 3155-0
    ISSN 1520-5126 ; 0002-7863
    ISSN (online) 1520-5126
    ISSN 0002-7863
    DOI 10.1021/ja305310r
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  9. Article ; Online: Microscopic Simulations of Charge Transport in Disordered Organic Semiconductors.

    Rühle, Victor / Lukyanov, Alexander / May, Falk / Schrader, Manuel / Vehoff, Thorsten / Kirkpatrick, James / Baumeier, Björn / Andrienko, Denis

    Journal of chemical theory and computation

    2011  Volume 7, Issue 10, Page(s) 3335–3345

    Abstract: Charge carrier dynamics in an organic semiconductor can often be described in terms of charge hopping between localized states. The hopping rates depend on electronic coupling elements, reorganization energies, and driving forces, which vary as a ... ...

    Abstract Charge carrier dynamics in an organic semiconductor can often be described in terms of charge hopping between localized states. The hopping rates depend on electronic coupling elements, reorganization energies, and driving forces, which vary as a function of position and orientation of the molecules. The exact evaluation of these contributions in a molecular assembly is computationally prohibitive. Various, often semiempirical, approximations are employed instead. In this work, we review some of these approaches and introduce a software toolkit which implements them. The purpose of the toolkit is to simplify the workflow for charge transport simulations, provide a uniform error control for the methods and a flexible platform for their development, and eventually allow in silico prescreening of organic semiconductors for specific applications. All implemented methods are illustrated by studying charge transport in amorphous films of tris-(8-hydroxyquinoline)aluminum, a common organic semiconductor.
    Language English
    Publishing date 2011-08-19
    Publishing country United States
    Document type Journal Article
    ISSN 1549-9626
    ISSN (online) 1549-9626
    DOI 10.1021/ct200388s
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  10. Article ; Online: Electric field controlled magnetic anisotropy in a single molecule.

    Zyazin, Alexander S / van den Berg, Johan W G / Osorio, Edgar A / van der Zant, Herre S J / Konstantinidis, Nikolaos P / Leijnse, Martin / Wegewijs, Maarten R / May, Falk / Hofstetter, Walter / Danieli, Chiara / Cornia, Andrea

    Nano letters

    2010  Volume 10, Issue 9, Page(s) 3307–3311

    Abstract: We have measured quantum transport through an individual Fe(4) single-molecule magnet embedded in a three-terminal device geometry. The characteristic zero-field splittings of adjacent charge states and their magnetic field evolution are observed in ... ...

    Abstract We have measured quantum transport through an individual Fe(4) single-molecule magnet embedded in a three-terminal device geometry. The characteristic zero-field splittings of adjacent charge states and their magnetic field evolution are observed in inelastic tunneling spectroscopy. We demonstrate that the molecule retains its magnetic properties and, moreover, that the magnetic anisotropy is significantly enhanced by reversible electron addition/subtraction controlled with the gate voltage. Single-molecule magnetism can thus be electrically controlled.
    Language English
    Publishing date 2010-08-05
    Publishing country United States
    Document type Journal Article
    ISSN 1530-6992
    ISSN (online) 1530-6992
    DOI 10.1021/nl1009603
    Database MEDical Literature Analysis and Retrieval System OnLINE

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