A5090987587- Molecular Junctions and Nanostructures
- Organic Electronics and Photovoltaics
- Conducting polymers and applications
- Surface and Thin Film Phenomena
- Organic Light-Emitting Diodes Research
- Machine Learning in Materials Science
- Thin-Film Transistor Technologies
- Surface Chemistry and Catalysis
- Luminescence and Fluorescent Materials
- Quantum Dots Synthesis And Properties
- Metal-Organic Frameworks: Synthesis and Applications
- Semiconductor materials and devices
- Graphene research and applications
- Nonlinear Optical Materials Studies
- Analytical Chemistry and Sensors
- Organic and Molecular Conductors Research
- X-ray Diffraction in Crystallography
- Nonlinear Optical Materials Research
- Quantum and electron transport phenomena
- nanoparticles nucleation surface interactions
- Photochromic and Fluorescence Chemistry
- Photochemistry and Electron Transfer Studies
- Synthesis and properties of polymers
- Nanowire Synthesis and Applications
- Advanced Chemical Physics Studies
Graz University of Technology
2016-2025
Nawi Graz
2015-2021
Institute of Solid State Physics
2009-2019
University of Milano-Bicocca
2006-2017
Helmholtz Institute Jena
2017
Friedrich Schiller University Jena
2017
University of Kaiserslautern
2017
Georgia Institute of Technology
2003-2012
Humboldt-Universität zu Berlin
2007-2010
Montanuniversität Leoben
2008-2010
The electronic properties and the function of hybrid inorganic-organic systems (HIOS) are intimately linked to their interface geometry. Here we show that inclusion many-body collective response substrate electrons inside inorganic bulk enables us reliably predict HIOS geometries energies. This is achieved by combination dispersion-corrected density-functional theory (the DFT+ van der Waals approach) [Phys. Rev. Lett. 102, 073005 (2009)], with Lifshitz-Zaremba-Kohn for nonlocal Coulomb...
Self-assembled monolayers (SAMs) of organic molecules generally modify the surface properties when covalently linked to substrates. In electronics, SAMs are used fine-tune work functions inorganic electrodes, thereby minimizing energy barriers for injection or extraction charge carriers into out an active layer; a detailed understanding interface energetics on atomistic scale is required design improved interfaces. field molecular SAM itself (or, in some cases, one few molecules) carries...
A comparative study of the two-photon absorption (TPA) properties octupolar compounds and their dipolar one-dimensional counterparts is presented on basis correlated quantum-chemical calculations. The roles dimensionality symmetry are first discussed a simple exciton picture where ground-state excited-state wavefunctions three-arm systems built from linear combination corresponding single-arm wavefunctions. This model predicts factor 3 increase in TPA cross section limiting case three...
The energetics at the interfaces between metal and monolayers of covalently bound organic molecules is studied theoretically. Despite under consideration displaying very different frontier orbital energies, highest occupied molecular levels are found to be pinned a constant energy offset with respect Fermi level. In contrast, properties strongly impact work function. These interfacial phenomena rationalized in terms charge fluctuations electrostatics atomic length scale as determined by...
Self-assembled monolayers (SAMs) of organic molecules provide an important tool to tune the work function electrodes in plastic electronics and significantly improve device performance. Also, energetic alignment frontier molecular orbitals SAM with Fermi energy a metal electrode dominates charge transport single-molecule devices. On basis first-principles calculations on SAMs π-conjugated noble metals, we detailed description mechanisms that give rise intrinsically link these interfacial...
Abstract The low emission band at 2.2–2.3 eV in polyfluorene‐based conjugated materials is studied by various spectroscopic methods on defined copolymers of 9–9′‐difarnesyl‐fluorene with 9‐fluorenone, which can be seen as a model compound for degraded polyfluorenes. Absorption, electroluminescence, and photoluminescence the film (temperature‐dependent) solution (room temperature) reveal optical properties this low‐energy emerging polyfluorene‐type polymers upon degradation. All experimental...
Interface energetics are of fundamental importance in organic and molecular electronics. By combining complementary experimental techniques first-principles calculations, we resolve the complex interplay among several interfacial phenomena that collectively determine electronic structure strong electron acceptor tetrafluoro-tetracyanoquinodimethane chemisorbed on copper. The combination adsorption-induced geometric distortion molecules, metal-to-molecule charge transfer, molecule-to-metal...
Chromophores based on a donor−acceptor−donor structure possessing large two-photon absorption cross section and one or two mono-aza-15-crown-5 ether moieties, which can bind metal cations, have been synthesized. The influence of Mg2+ binding their one- spectroscopic properties has investigated. Upon binding, the action sections at 810 nm decrease by factor up to 50 high concentrations this results in contrast excited fluorescence signal between bound unbound forms, for excitation range 730...
Extended bis(donor)-substituted squaraine chromophores exhibit very high two-photon cross-sections (as as 33 000 GM) in the near-IR; these can be attributed to combination of large transition dipoles with small detuning energies. The modulus third-order nonlinear optical susceptibility at 1.3 mum has been found 7.0 x 10-11 esu for one chromophores.
Poly(fluorene)-type materials are widely used in polymer-based light emitting devices. In their pristine state, they emit the deep blue spectral region. During operation there appears, however, an additional emission peak at around 2.3 eV. This observation has usually been attributed to aggregate or excimer formation. Recently, it shown that photo- and/or electro-oxidation of poly(fluorene) chains resulting ketonic defects (i.e., formation fluorenone groups) can also be held responsible for...
A thorough understanding of the adsorption molecules on metallic surfaces is a crucial prerequisite for development and improvement functionalized materials. prominent representative within class π-conjugated 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) which, adsorbed Ag(111), Au(111) or Cu(111) surfaces, shows characteristic trends work-function modification, alignment molecular levels with substrate Fermi energy binding distances. We carried out density functional theory...
The focus of the present article is on understanding insight that X-ray photoelectron spectroscopy (XPS) measurements can provide when studying self-assembled monolayers. Comparing density functional theory calculations to experimental data deliberately chosen model systems, we show both chemical environment and electrostatic effects arising from a superposition molecular dipoles influence measured core-level binding energies significant degree. crucial role often overlooked in polar...
Abstract The presence of dipolar layers determines the functionality most technologically relevant interfaces. present contribution reviews how periodic dipole assemblies modify properties such interfaces through so‐called collective electrostatic effects. They impact ionization energies and electron affinities thin films, change work function metallic semiconducting substrates, determine alignment electronic states at Dipolar originate either from assembly polar molecules or they arise...
Density functional theory with optimally tuned range-separated hybrid (OT-RSH) functionals has been recently suggested [Refaely-Abramson et al. Phys. Rev. Lett.2012, 109, 226405] as a nonempirical approach to predict the outer-valence electronic structure of molecules same accuracy many-body perturbation theory. Here, we provide quantitative evaluation OT-RSH by examining its performance in predicting electron spectra several prototypical gas-phase molecules, from aromatic rings (benzene,...
Using a representative model system, here electronic and structural properties of aromatic self‐assembled monolayers (SAMs) are described that contain an embedded, dipolar group. As polar unit, pyrimidine is used, with its orientation in the molecular backbone and, consequently, direction embedded dipole moment being varied. The these embedded‐dipole SAMs thoroughly analyzed using number complementary characterization techniques combined quantum‐mechanical modeling. It shown such...
Abstract Based on the powerful concept of embedded dipole self‐assembled monolayers (SAMs), highly conductive interfacial layers are designed, which allow tuning contact resistance organic thin‐film transistors over three orders magnitude with minimum values well below 1 kΩ cm. This not only permits realization competitive p‐type (pentacene‐based) devices rigid as flexible substrates, but also enables n‐type (C 60 ‐based) comparable characteristics utilizing same electrode material (Au). As...
Three new dipolar chromophores based on a diaklyaminophenyl donor, pyrrole auxiliary thiazole acceptor, and strong heterocyclic acceptors have been synthesized. For one of these compounds we measured very large non-degenerate two-photon cross section ca. 1500 GM in the near-IR telecommunications range using pump-probe technique. Calculations indicate for degenerate absorption is likely to be 60% this value.
The electron-donor abilities of ten aminophenyl systems and an additional aminothienyl system are compared using density functional theory calculations. studied here include those with amine nitrogen atoms bearing alkyl or aryl groups as part a heterocycle. Their to act donors in electron-transfer processes assessed from calculated vertical ionization potentials for the aminobenzenes, which good agreement available experimental data. intramolecular pi-electron conjugated inferred bond...
The degenerate and nondegenerate two-photon absorption (2PA) spectra for a symmetric an asymmetric fluorene derivative were experimentally measured in order to determine the effect of intermediate state resonance enhancement (ISRE) on 2PA cross section δ. ability tune individual photon energies (ND-2PA) process afforded quantitative study ISRE without modifying chemical structure investigated chromophores. Both molecules exhibited resonant nonlinearity with compound showing as much...
We apply correlated quantum-chemical techniques to study the origin of large two-photon absorption (TPA) cross sections, δ, in stilbene derivatives which electron-donating and electron-withdrawing substituents provide a quadrupolar charge-transfer arrangement. An additional field created by set point charges is used systematically modify ground-state polarization determine its consequences for TPA response. The effect on molecular structure can be quantified evolution π-bond-order...