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Letteratura scientifica selezionata sul tema "Polaron delocalization"

Autore: Grafiati

Pubblicato: 21 dicembre 2024

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Articoli di riviste sul tema "Polaron delocalization"

Rawson, Jeff, Paul J. Angiolillo e Michael J. Therien. "Extreme electron polaron spatial delocalization in π-conjugated materials". Proceedings of the National Academy of Sciences 112, n. 45 (28 ottobre 2015): 13779–83. http://dx.doi.org/10.1073/pnas.1512318112.

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The electron polaron, a spin-1/2 excitation, is the fundamental negative charge carrier in π-conjugated organic materials. Large polaron spatial dimensions result from weak electron-lattice coupling and thus identify materials with unusually low barriers for the charge transfer reactions that are central to electronic device applications. Here we demonstrate electron polarons in π-conjugated multiporphyrin arrays that feature vast areal delocalization. This finding is evidenced by concurrent optical and electron spin resonance measurements, coupled with electronic structure calculations that suggest atypically small reorganization energies for one-electron reduction of these materials. Because the electron polaron dimension can be linked to key performance metrics in organic photovoltaics, light-emitting diodes, and a host of other devices, these findings identify conjugated materials with exceptional optical, electronic, and spintronic properties.

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VASILIU-DOLOC, L., R. OSBORN, S. ROSENKRANZ, J. MESOT, J. F. MITCHELL, S. K. SINHA, O. H. SEECK, J. W. LYNN e Z. ISLAM. "POLARON ORDERING IN FERROMAGNETIC COLOSSAL MAGNETORESISTIVE OXIDES". International Journal of Modern Physics B 14, n. 29n31 (20 dicembre 2000): 3711–18. http://dx.doi.org/10.1142/s021797920000426x.

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We review our recent x-ray and neutron scattering studies that reveal static diffuse scattering due to polarons in the paramagnetic phase of the colossal magnetoresistive manganites La 2-2x Sr 1+2x Mn 2 O 7, with x=0.40 and 0.44. We show that the polarons exhibit short-range incommensurate correlations that grow with decreasing temperature, but disappear abruptly at the combined ferromagnetic and metal-insulator transition in the x=0.40 system because of the sudden charge delocalization, while persisting at low temperature in the antiferromagnetic x=0.44 system. The "melting" of the polaron ordering as we cool through TC occurs with the collapse of the polaron scattering itself in the x=0.40 system. The polaron order is characterized by an ordering wave vector q=(0.3,0,1) that is almost independent of x for x≥0.40, and is consistent with a model of disordered stripes.

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Ghosh, Raja, Christopher M. Pochas e Frank C. Spano. "Polaron Delocalization in Conjugated Polymer Films". Journal of Physical Chemistry C 120, n. 21 (19 maggio 2016): 11394–406. http://dx.doi.org/10.1021/acs.jpcc.6b02917.

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Yan, X. Z., J. Pawlas, T. Goodson e J. F. Hartwig. "Polaron Delocalization in Ladder Macromolecular Systems". Journal of the American Chemical Society 127, n. 25 (giugno 2005): 9105–16. http://dx.doi.org/10.1021/ja050184n.

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Matheson, Andrew B., Arvydas Ruseckas, Scott J. Pearson e Ifor D. W. Samuel. "Hole delocalization as a driving force for charge pair dissociation in organic photovoltaics". Materials Horizons 6, n. 5 (2019): 1050–56. http://dx.doi.org/10.1039/c8mh01204k.

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Feng, Tao, Liping Li, Quan Shi, Shengde Dong, Baoyun Li, Ke Li e Guangshe Li. "Evidence for the influence of polaron delocalization on the electrical transport in LiNi0.4+xMn0.4−xCo0.2O2". Physical Chemistry Chemical Physics 22, n. 4 (2020): 2054–60. http://dx.doi.org/10.1039/c9cp05768d.

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MUKHOPADHYAY, SOMA, e ASHOK CHATTERJEE. "EFFECT OF MULTIPLE PHONON BRANCHES ON THE PHASE TRANSITIONAL BEHAVIOR OF A TWO-DIMENSIONAL POLARON GAS". International Journal of Modern Physics B 09, n. 07 (30 marzo 1995): 849–57. http://dx.doi.org/10.1142/s0217979295000331.

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Using an all-coupling variational method and the random phase approximation, it is shown that a two-dimensional polaron gas exhibiting no localization-delocalization transition with a single optical phonon branch may undergo such a transition in the presence of an additional phonon branch. However, if the system already shows a transition, with a single phonon branch, then the effect of an additional branch is just to enhance the low-mobility self-trapped phase of the polaron.

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Steyrleuthner, Robert, Yuexing Zhang, Lei Zhang, Felix Kraffert, Benjamin P. Cherniawski, Robert Bittl, Alejandro L. Briseno, Jean-Luc Bredas e Jan Behrends. "Impact of morphology on polaron delocalization in a semicrystalline conjugated polymer". Physical Chemistry Chemical Physics 19, n. 5 (2017): 3627–39. http://dx.doi.org/10.1039/c6cp07485e.

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Fialko, N. S., e V. D. Lakhno. "Numerical Simulation of Small Radius Polaron in a Chain with Random Perturbations". Mathematical Biology and Bioinformatics 14, n. 1 (10 aprile 2019): 126–36. http://dx.doi.org/10.17537/2019.14.126.

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In a number of publications about biophysical experiments on the transfer of a charge to DNA, it is assumed that charge is transferred via a super-exchange mechanism at short distances of 2–3 nucleotide pairs, and in long fragments the charge forms a polaron that moves along the chain under the influence of temperature fluctuations. Using numerical simutation, we investigate the dynamics of a polaron of small radius in a homogeneous chain plaiced in constant electric field at a finite temperature. It is shown that there is no charge transfer by the polaron mechanism, i.e. there is no sequential movement of the polaron from site to site, in chains with parameter valuess corresponding to homogeneous adenine DNA fragments. The “polaron or delocalized state” check is based on the control of the average characteristics: the delocalization parameter, the position of the maximum probability, and the maximum modulus displacement. The dynamics of individual trajectories is also considered. Without electric field, there is a mode of switching between the states "stationary polaron – delocalized state", and a new polaron arises at a random site of the chain. In the chain placed in field with constant intensity, the averaged charge moves in the direction of the field, but the transfer occurs in a delocalized state.

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Ji, Xiaozhou, Mingwan Leng, Haomiao Xie, Chenxu Wang, Kim R. Dunbar, Yang Zou e Lei Fang. "Extraordinary electrochemical stability and extended polaron delocalization of ladder-type polyaniline-analogous polymers". Chemical Science 11, n. 47 (2020): 12737–45. http://dx.doi.org/10.1039/d0sc03348k.

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Più fonti

Tesi sul tema "Polaron delocalization"

Golushko, Andrei. "Polymères supramoléculaires à base de macrocycles triarylamines : synthèses et propriétés". Electronic Thesis or Diss., Strasbourg, 2024. http://www.theses.fr/2024STRAF034.

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Dans ce travail, deux nouveaux macrocycles hexaazaparacyclophane (HAPC) à base de triarylamine ont été synthétisés avec trois groupes amide périphériques de liaison hydrogène ayant des arrangements relatifs différents. Des interactions faibles permettent aux molécules obtenues de former des empilements colonnaires unidimensionnels, et le mécanisme de polymérisation supramoléculaire de ce processus a été étudié pour la première fois dans la recherche sur les HAPC à l'aide de la spectroscopie, de la microscopie et des calculs DFT. Il a été constaté que les substituants amide en positions 1,2,3 à la périphérie des macrocycles hexagonaux favorisent un mécanisme isodésmique et la formation de fibres courtes et rigides, tandis que les molécules avec des substituants en positions 1,3,5 forment des fibres longues et flexibles dans un mécanisme de polymérisation coopérative. La présence de six atomes d'azote conjugués à travers des anneaux phényles implique une multi-activité redox et potentiellement de riches propriétés optoélectroniques. L'oxydation des fibres auto-assemblées a montré une délocalisation des polarons générés dans le plan macrocyclique et le long des empilements supramoléculaires, similaire aux résultats rapportés précédemment. Pour le macrocycle avec substitution consécutive, les données indiquent une plus grande délocalisation des polarons dans le plan à des états d'oxydation plus faibles, en comparaison avec le macrocycle à périphéries alternées et entièrement substituées. De telles fibres supramoléculaires oxydées pourraient servir de matériaux précieux avec une haute densité de spin dans le domaine de l'électronique organique
In this work, two new triarylamine-based hexaazaparacyclophane (HAPC) macrocycles were synthesized with three peripheral hydrogen-bonding amide groups having different relative arrangements. Weak interactions allow the obtained molecules to form one-dimensional columnar stacks, and the supramolecular polymerization mechanism of this process was investigated for the first time in HAPCs research with spectroscopy, microscopy, and DFT-calculations. It was found that amide substituents in positions 1,2,3 on the periphery of hexagonal macrocycles promote isodesmic mechanism and the formation of short rigid fibers, while the molecules with substituents in positions 1,3,5 form long flexible fibers in cooperative polymerization mechanism. The presence of six nitrogen atoms conjugated through phenyl rings implies multi-redox activity and potentially rich optoelectronic properties. The oxidation of self-assembled fibers showed delocalization of the generated polarons in the macrocyclic plane and along the supramolecular stacks, similar to the previously reported results. For the macrocycle with consecutive substitution, the data indicates a greater in-plane polaron delocalization at lower oxidation states, in comparison to the macrocycle with alternating and fully substituted peripheries. Such oxidized supramolecular fibers might serve as valuable materials with a high spin density in the domain of organic electronics

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Capitoli di libri sul tema "Polaron delocalization"

Wells, P. R., S. Ehrenson e R. W. Taft. "Substituent Effects in the Naphthalene Series. An Analysis of Polar and pI Delocalization Effects". In Progress in Physical Organic Chemistry, 147–322. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2007. http://dx.doi.org/10.1002/9780470171851.ch4.

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Clugston, Michael, Malcolm Stewart e Fabrice Birembaut. "Bonding and Molecular Shape". In Making the Transition to University Chemistry. Oxford University Press, 2021. http://dx.doi.org/10.1093/hesc/9780198757153.003.0002.

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This chapter discusses bonding and molecular shape of electrons. A covalent bond occurs when atoms share a pair of similar electrons. Modern theories on covalent bonding are dominated by molecular orbital theory. Polar covalent bonds occur when different atoms share the electron pair unequally due to electronegativity. With benzene being the most familiar molecule of the bonding, delocalization happens when more than two atoms are involved in the bonding. The valence-shell electron-pair repulsion (VSEPR) theory can help us to visualize the shapes of simple molecules. Additionally, ionic bonding occurs when an atom transfers an electron to another atom and the ions formed a crystal lattice electrostatically.

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Perkins, John. "Energetics, kinetics, and mechanism". In Radical Chemistry: The Fundamentals. Oxford University Press, 2000. http://dx.doi.org/10.1093/hesc/9780198792895.003.0003.

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This chapter reviews some basic aspects of the energetics and kinetics of radical processes and the factors that determine them. It examines the decomposition of a dilute solution of a diacyl peroxide in an unreactive, non-polar medium, such as benzene. It also provides a kinetic analysis of the use of peroxide to initiate a chain reaction in which an alkene is polymerized, and demonstrates how slow propagations may compete with diffusion-controlled termination. The chapter discusses the modest stabilization found with alkyl-substituted methyl radicals that can be attributed in part to hyperconjugation, which is revealed both by theory and by spectroscopic data. The chapter finally explains that stabilization is a thermodynamic property that arise from electron delocalization.

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Frey, Perry A., e Adrian D. Hegeman. "Acyl Group Transfer: Proteases and Esterases". In Enzymatic Reaction Mechanisms. Oxford University Press, 2007. http://dx.doi.org/10.1093/oso/9780195122589.003.0010.

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Acyl group transfer processes are plentiful in enzymatic reactions. Examples may be found in ATP-dependent ligation in chapter 11, carbon-carbon bond formation in chapter 14, and fatty acid biosynthesis in chapter 18. In this chapter, we begin by presenting the basic chemistry of acyl group transfer. We then consider four major classes of proteases that catalyze acyl group transfer in the hydrolysis of peptide bonds. Acyl group transfer is so common in organic and biochemistry that the chemistry by which it occurs is often taken for granted. Early studies provided evidence for a mechanism initiated by nucleophilic addition of the acyl group acceptor to the carbonyl group to form a tetrahedral intermediate, analogous to the reversible addition of a nucleophilic molecule to the carbonyl group of an aldehyde or ketone. A mechanism of this type is shown in scheme 6-1 for acyl group transfer from a group :X to a nucleophile :G catalyzed by a general base. This mechanism is drawn from a larger family of possible mechanisms involving specific acid-base, general acid, general base, or concerted general acid-base catalysis of nucleophilic addition to an acyl carbonyl group to form a tetrahedral intermediate, followed by the elimination of :X–H to produce the new acyl compound. In enzymatic reactions the nucleophilic atom G in scheme 6-1 is normally nitrogen, oxygen, sulfur, or a carbanionic species. An acyl carbonyl group is less polar and correspondingly less reactive toward nucleophilic addition than an aldehyde or ketone. The reason is the effect on the heteroatom of nonbonding electrons, which reside in p orbitals that overlap the π orbital of the carbonyl group. The consequent delocalization of electrons stabilizes the carbonyl group and attenuates its reactivity with nucleophiles. Other factors being equal, the order of reactivity is thioester > ester > amide, which is the inverse of the degree of delocalization. Delocalization is least in thioesters because of the high energy of the sulfur p orbitals, which reside in the next higher principal quantum number relative to oxygen in the acyl carbonyl group.

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Atti di convegni sul tema "Polaron delocalization"

Russo, Mattia, Kyriacos Georgiou, Armando Genco, Simone De Liberato, Giulio Cerullo, David G. Lidzey, Andreas Othonos, Margherita Maiuri e Tersilla Virgili. "Direct Evidence of Ultrafast Energy Delocalization in a Strongly Coupled Organic Microcavity probed by Two-Dimensional Electronic Spectroscopy". In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/up.2022.m2a.7.

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Two-Dimensional Electronic Spectroscopy reveals an ultrafast energy delocalization between 2μm distanced donor/acceptor molecules confined in a microcavity. This mechanism is promoted by the formation of hybrid-polariton states that induces a coupling in the entire system.

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Maiuri, Margherita, Mattia Russo, Kyriakos Georgiou, Armando Genco, Simone De Liberato, Giulio Cerullo, David Lidzey, Andreas Othonos e Tersilla Virgili. "Polariton-assisted ultrafast energy delocalization in a donor-acceptor organic microcavity probed by two-dimensional electronic spectroscopy". In Physical Chemistry of Semiconductor Materials and Interfaces XXII, a cura di Andrew J. Musser e Derya Baran. SPIE, 2023. http://dx.doi.org/10.1117/12.2681450.

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Fei, Haosheng, Xicheng Ai, Li Han, Ruijuan Nie e Zhenhua Hu. "Surface Effect On The Nonlinear Optical Properties Of Transition Metal-Oxode Microcrystallites". In Nonlinear Optics. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/nlo.1992.we15.

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The size dependent modifications of the optical and electronic properties of microcrystallites have attracted considerable attention recently[1-4]. As the diameter of the microcrystallite approaches its corresponding exciton Bohr diameter, its electronic and optical properties start to change because of the quantum confinement effect, dielectric effect and the effect of the surface[5]. For microcrystallites in such a small size regime, a large percentage of the atomes is on or near the surfaces. The existence of this vast interface between the microcrystallite and the surrounding medium can have a profound effect on the nonlinear optical properties of the microcrystallites. For the first time, we studied the nonlinear optical properties of translation metal-oxide microcrystallites by coating the surface with a layer of organic polar molecule(DBS etc.), and found that the change of the surface environment could alter the optical properties greatly. For Fe2O3 as example, (1) the absorption incresed toward the high energy side, (2) the laser induced luminescence intensity decreased by 2 orders in magnitude, and on the contrary, the Raman signal of the surface was enhanced greatly, (3) the saturable absorption phenomenon disappeared, (4) larger third order susceptibility and faster excited state relaxation were obtained compared with uncoated Fe2O3 microcrystallite. These phenomena are the results of the change of the electronic structure caused by the quantum confinement effect and the effect of the surface, unlike semiconductor microcrystallites in which the delocalized Wannier excitons can be influenced greatly by the quantum confinement effect (such as PbS microcrystallite). Transition metal oxide microcrystallite has more complicated electronic structure in which localized d electrons influence its electronic and optical properties greatly[6], and the small diameter Frenkel exciton in such material was effected little by the quantum confinement effect, therefore, the exciton structure could not be abserved in the absorption spectrum. But the size of the transition metal oxide microcrystallites influence their electronic structure strongly. For Fe2O3 as example, the energy structure can be quantitatively shown as the Figure (at the end of the paper), in which a is d-d transition, b represents charge transfer, c is orbital promotion and d is interband transitions. As the size of the microcrystallite decreases, the 3d and 4sp state couples increasingly, and the 3d-4sp (orbital promotion) state contribution increases correspondingly. To some extend, the d electrons and the Frenkel exciton will be delocalized, and the excited electron-hole pair can be ionized and scattered to the surface rapidly. In particular, when the surface was coated with a layer of organic polar molecule, the 3d-4sp state interaction was enhanced greatly under the strong polar interaction of the surface, and some 3d-4sp hydride state will exist, thus the d electrons and the Frenkel exciton will became more delocalization, and the laser induced electron-hole pairs interect and scatter to the surface very fast, so the surface delocalization state generate, accumulate and relax very rapidly and the electron-electron coherence effect[7] is enhanced greatly. Such changes not only increased the nonlinear response, but also resulted in shorter lifetime and stronger nonraditive process.

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