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Search Results: 1 - 10 of 191377 matches for " D. Beljonne "
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Breakdown of the mirror image symmetry in the optical absorption/emission spectra of oligo(para-phenylene)s
G. Heimel,M. Daghofer,J. Gierschner,E. J. W. List,A. C. Grimsdale,K. Müllen,D. Beljonne,J. -L. Brédas,E. Zojer
Physics , 2005, DOI: 10.1063/1.1839574
Abstract: The absorption and emission spectra of most luminescent, pi-conjugated, organic molecules are the mirror image of each other. In some cases, however, this symmetry is severely broken. In the present work, the asymmetry between the absorption and fluorescence spectra in molecular systems consisting of para-linked phenyl rings is studied. The vibronic structure of the emission and absorption bands is calculated from ab-initio quantum chemical methods and a subsequent, rigorous Franck-Condon treatment. Good agreement with experiment is achieved. A clear relation can be established between the strongly anharmonic double-well potential for the phenylene ring librations around the long molecular axis and the observed deviation from the mirror image symmetry. Consequences for related compounds and temperature dependent optical measurements are also discussed.
Charge-transfer excitons in strongly coupled organic semiconductors
Jean-Francois Glowe,Mathieu Perrin,David Beljonne,Sophia C. Hayes,Fabrice Gardebien,Carlos Silva
Physics , 2009, DOI: 10.1103/PhysRevB.81.041201
Abstract: Time-resolved and temperature-dependent photoluminescence measurements on one-dimensional sexithiophene lattices reveal intrinsic branching of photoexcitations to two distinct species: self-trapped excitons and dark charge-transfer excitons (CTX; > 5% yield), with radii spanning 2-3 sites. The significant CTX yield results from the strong charge-transfer character of the Frenkel exciton band due to the large free exciton bandwidth (~400 meV) in these supramolecular nanostructures.
Coherent vs Thermally Activated Singlet Exciton Fission in Acene Derivatives From First Principles Quantum Dynamics Simulations: Molecular Packing Makes the Difference
Hiroyuki Tamura,Miquel Huix-Rotllant,Irene Burghardt,Yoann Olivier,David Beljonne
Physics , 2015,
Abstract: The mechanisms underlying coherent and thermally activated singlet exciton fission in pi-stacked acene crystals are clarified based on quantum dynamics simulations parameterized against a highly correlated description of the electronic excitations and their couplings to intramolecular and intermolecular vibrations. In TIPS-pentacene crystals, the relative longitudinal shift of the molecular backbones yields large electronic couplings of the triplet exciton pair with both the singlet exciton and charge transfer (CT) states. CT-mediated superexchange and direct pathways are found to contribute synergetically to the ultrafast (100fs) singlet fission process driven by vibronic coherences. By contrast, the electronic couplings for singlet fission strictly vanish at the equilibrium pi-stacking of rubrene that exhibits C2h symmetry. In this case, the process is incoherent and driven by excitations of symmetry-breaking intermolecular vibrations, rationalizing the experimentally observed temperature dependence.
Charge separation by photoexcitation in semicrystalline polymeric semiconductors: An intrinsic or extrinsic mechanism?
Francis Paquin,Gianluca Latini,Maciej Sakowicz,Paul-Ludovic Karsenti,Linjun Wang,David Beljonne,Natalie Stingelin,Carlos Silva
Physics , 2011, DOI: 10.1103/PhysRevLett.106.197401
Abstract: We probe charge photogeneration and subsequent recombination dynamics in neat regioregular poly(3-hexylthiophene) films over six decades in time by means of time-resolved photoluminescence spectroscopy. Exciton dissociation at 10K occurs extrinsically at interfaces between molecularly ordered and disordered domains. Polaron pairs thus produced recombine by tunnelling with distributed rates governed by the distribution of electron-hole radii. Quantum-chemical calculations suggest that hot-exciton dissociation at such interfaces results from a high charge-transfer character.
The Role of Driving Energy and Delocalised States for Charge Separation in Organic Semiconductors
Artem A. Bakulin,Akshay Rao,Vlad G. Pavelyev,Paul H. M. van Loosdrecht,Maxim S. Pshenichnikov,Dorota Niedzialek,Jér?me Cornil,David Beljonne,Richard H. Friend
Physics , 2013, DOI: 10.1126/science.1217745
Abstract: The electron-hole pair created via photon absorption in organic photoconversion systems must overcome the Coulomb attraction to achieve long-range charge separation. We show that this process is facilitated through the formation of excited, delocalized band states. In our experiments on organic photovoltaic cells, these states were accessed for a short time (<1ps) via IR optical excitation of electron-hole pairs bound at the heterojunction. Atomistic modelling showed that the IR photons promote bound charge pairs to delocalised band states, similar to those formed just after singlet exciton dissociation, which indicates that such states act as the gateway for charge separation. Our results suggest that charge separation in efficient organic photoconversion systems, occurs through hot-state charge delocalisation rather than energy-gradient-driven intermolecular hopping.
Electrical Conductivity of Collapsed Multilayer Graphene Tubes  [PDF]
D. Mendoza
World Journal of Nano Science and Engineering (WJNSE) , 2012, DOI: 10.4236/wjnse.2012.22009
Abstract: Synthesis of multilayer graphene on copper wires by a chemical vapor deposition method is reported. After copper etching, the multilayer tube collapses forming stripes of graphitic films, their electrical conductance as a function of temperature indicate a semiconductor-like behavior. Using the multilayer graphene stripes, a cross junction is built and owing to its electrical behavior we propose that a tunneling process exists in the device.
Porous Carbon Grown by Chemical Vapor Deposition on Copper Substrates  [PDF]
D. Mendoza
Journal of Materials Science and Chemical Engineering (MSCE) , 2015, DOI: 10.4236/msce.2015.38003
Abstract: Amorphous porous carbon was synthesized by chemical vapor deposition on copper substrates. The average size of the pores is around 1.2 microns with some small pores decorating the big ones. Lamellar samples of this carbonaceous material can be separated from the copper support and may be useful as electrode due to its low electrical resistivity of the order of 0.4 Ωcm.
Application of Enzyme Extracted from Aloe vera Plant in Chemical Pretreatment of Cotton Knitted Textile to Reduce Pollution Load  [PDF]
D. Jothi
World Journal of Engineering and Technology (WJET) , 2015, DOI: 10.4236/wjet.2015.33B007

Nowadays, highly alkaline chemicals like caustic soda, soda ash, silicate, acetic acid and soaping agents are used for scouring to remove the non-cellulosic impurities from the cotton. Using 30 - 40 gm/Kg on weight of the fabric results in destruction of cotton structure. Intensive rinsing and more acid is needed for reutilization of cotton, which enlarges the volume of effluent. Furthermore, these hazards chemicals result in increase in COD, BOD and TDS in waste water. These chemicals also attack the cellulose leading to heavy strength loss and weight loss in the fabric. The net result is low quality control and polluted environment with high usage of energy, time, chemical and water. Aloe vera presents the finest commercial opportunity in various industrial sectors among the various plants. Also, most of the countries are gifted with the unique geographical features that are essential for cultivation of Aloe vera. Yet, none of the country has realized and reaped the full potential of such plants in various industrial applications. The reason is simple: lack of the requisite expertise in extraction of various enzymes present in aloe plant. Fortunately, the technology is now accessible to make use of enzyme in textile application. In this research an attempt has been made to make use of lipase enzyme extracted from aloe plant in textile chemical pre- treatment process. In the present research work, an attempt was made to develop bio scouring of 100% cotton knitted fabric with lipase enzyme extracted from Aloe deberena plant at various concentration (1%, 2% and 3%) at various temperature (40?C, 60?C and 70?C) for a period of 30 minutes, 60 minutes and 90 minutes. The properties of bio scoured fabrics are compared with these of conventional scoured one. Encouraging results in terms of dye uptake, dye levelness, wash fastness, light fastness and rubbing fastness are obtained in case of bio scouring fabric dyed with dark reactive colors. Further, it reduces volume of effluent as well as COD, TDS and pH. It saves a substantial thermal energy 50% and electrical energy 40%. Bio scouring waste water has 40% - 50% less COD and 60% less TDS as compared to conventional scouring waste water.

Hyporheic Zone Hydrochemistry of the Mine-Polluted River  [PDF]
D. Ciszewski
Journal of Geoscience and Environment Protection (GEP) , 2015, DOI: 10.4236/gep.2015.310008

Intensity of stream waters mixing with groundwaters and lateral extent of these processes in the hyporheic zone were investigated in a near-bank sandbar and an adjacent floodplain through the comparison of groundwaters and stream water chemistry of the Bia?a Przemsza River in southern Poland. The stream waters were polluted by the discharge of mine waters from “Boles?aw” lead and zinc mine. The investigated waters were several times more mineralized than the natural spring waters of the river valley. The concentration of: potassium, sodium, and the pH, as well as cadmium, lead, and zinc decreased in the hyporheic zone towards the stream bank, whereas conductance, calcium, magnesium, sulphates, as well as silica contents were the highest on the floodplain, diminishing towards the stream. The changes observed in the chemical composition of groundwaters were apparent in mixing stream waters below the depth of 2 m with shallow groundwaters draining the valley slope. Hyporheic mixing also takes place in the 10-meter-wide, marginal zone of the sandbar, whereas in the 5-meter-wide stream-side zone of the sandbar groundwaters represent weakly transformed stream water.

Fractional Topological Insulators—A Bosonization Approach  [PDF]
D. Schmeltzer
Journal of Modern Physics (JMP) , 2016, DOI: 10.4236/jmp.2016.71012
Abstract: A metallic disk with strong spin orbit interaction is investigated. The finite disk geometry introduces a confining potential. Due to the strong spin-orbit interaction and confining potential the metal disk is described by an effective one-dimensional model with a harmonic potential. The harmonic potential gives rise to classical turning points. As a result, open boundary conditions must be used. We bosonize the model and obtain chiral Bosons for each spin on the edge of the disk. When the filling fraction is reduced to \"\" the electron-electron interactions are studied by using the Jordan Wigner phase for composite fermions which give rise to a Luttinger liquid. When the metallic disk is in the proximity with a superconductor, a Fractional Topological Insulator is obtained. An experimental realization is proposed. We show that by tunning the chemical potential we control the classical turning points for which a Fractional Topological Insulator is realized.
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