Bibliografie tematiche / Electronic delocalisation

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Letteratura scientifica selezionata sul tema "Electronic delocalisation"

Autore: Grafiati

Pubblicato: 25 gennaio 2025

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Articoli di riviste sul tema "Electronic delocalisation"

Kahmann, Simon, Maria A. Loi e Christoph J. Brabec. "Delocalisation softens polaron electronic transitions and vibrational modes in conjugated polymers". Journal of Materials Chemistry C 6, n. 22 (2018): 6008–13. http://dx.doi.org/10.1039/c8tc00909k.

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Men, Shuang, Peter Licence, Chi-Linh Do-Thanh, Huimin Luo e Sheng Dai. "X-ray photoelectron spectroscopy of piperidinium ionic liquids: a comparison to the charge delocalised pyridinium analogues". Physical Chemistry Chemical Physics 22, n. 21 (2020): 11976–83. http://dx.doi.org/10.1039/d0cp01454k.

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Reibnegger, Gilbert. "An ab initio and density functional theory study on neutral pterin radicals". Pteridines 26, n. 4 (1 dicembre 2015): 135–42. http://dx.doi.org/10.1515/pterid-2015-0008.

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AbstractThe electronic structures of the five radicals resulting from homolytic elimination of one of the hydrogen atoms from the most stable tautomeric form of neutral pterin were investigated in gas phase as well as in aqueous solution. Molecular wave functions obtained by density functional theory were analysed by quantum theory of atoms in molecules and electron localisation functions (ELF). Spin densities of the radicals as well as electrostatic potential functions were analysed. Radicals resulting from elimination of N-bonded hydrogen atoms are more stable in comparison with radicals obtained after abstraction of C-bonded hydrogen atoms. N-centred radicals show strong delocalisation of spin density over both heteroaromatic rings; in C-centred radicals delocalisation does not occur. ELF analyses showed that in N-derived radicals particularly the lone electron pair at N2′ is strongly involved into the bicyclic heteroaromatic π-electron system. Thereby, bonding geometry at N2′ in these radicals changes from pyramidal to planar. Transition from gas phase to solution phase (water) generally leads to increased polarity of the structures. Pterin-derived free radicals have been implicated in several biologically important reactions; so this investigation provides first insights into the detailed electronic structures of such molecular systems.

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Schubert, Gerald, Alexander Weiße e Holger Fehske. "Delocalisation transition in chains with correlated disorder". Physica B: Condensed Matter 359-361 (aprile 2005): 801–3. http://dx.doi.org/10.1016/j.physb.2005.01.232.

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Wu, Guanglu, István Szabó, Edina Rosta e Oren A. Scherman. "Cucurbit[8]uril-mediated pseudo[2,3]rotaxanes". Chemical Communications 55, n. 88 (2019): 13227–30. http://dx.doi.org/10.1039/c9cc07144j.

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Martinez-Felipe, Alfonso, Fraser Brebner, Daniel Zaton, Alberto Concellon, Sara Ahmadi, Milagros Piñol e Luis Oriol. "Molecular Recognition via Hydrogen Bonding in Supramolecular Complexes: A Fourier Transform Infrared Spectroscopy Study". Molecules 23, n. 9 (6 settembre 2018): 2278. http://dx.doi.org/10.3390/molecules23092278.

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We assess the assembly of supramolecular complexes by hydrogen bonding between azocompounds and a diacylaminopyridine monomer by temperature-dependent Fourier transform infrared spectroscopy (FT-IR) and density functional theory (DFT) calculations. The electronic delocalisation in the supramolecular rings formed by multiple hydrogen bonds stabilises the complexes, which coexist with dimeric species in temperature-dependent equilibria. We show how the application of readily available molecular modelling and spectroscopic techniques can predict the stability of new supramolecular entities coexisting in equilibria, ultimately assessing the success of molecular recognition.

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Vacher, Morgane, Fabio E. A. Albertani, Andrew J. Jenkins, Iakov Polyak, Michael J. Bearpark e Michael A. Robb. "Electron and nuclear dynamics following ionisation of modified bismethylene-adamantane". Faraday Discussions 194 (2016): 95–115. http://dx.doi.org/10.1039/c6fd00067c.

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We have simulated the coupled electron and nuclear dynamics using the Ehrenfest method upon valence ionisation of modified bismethylene-adamantane (BMA) molecules where there is an electron transfer between the two π bonds. We have shown that the nuclear motion significantly affects the electron dynamics after a few fs when the electronic states involved are close in energy. We have also demonstrated how the non-stationary electronic wave packet determines the nuclear motion, more precisely the asymmetric stretching of the two π bonds, illustrating “charge-directed reactivity”. Taking into account the nuclear wave packet width results in the dephasing of electron dynamics with a half-life of 8 fs; this eventually leads to the equal delocalisation of the hole density over the two methylene groups and thus symmetric bond lengths.

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Campo, Javier, Javier Luzón, Fernando Palacio, Garry J. McIntyre e Eric Ressouche. "Effect of spin delocalisation in K2FeCl5·H2O on its superexchange pathways". Physica B: Condensed Matter 335, n. 1-4 (luglio 2003): 15–18. http://dx.doi.org/10.1016/s0921-4526(03)00181-9.

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Gilmour, J. T. A., e N. Gaston. "Design of superatomic systems: exploiting favourable conditions for the delocalisation of d-electron density in transition metal doped clusters". Physical Chemistry Chemical Physics 22, n. 33 (2020): 18585–94. http://dx.doi.org/10.1039/d0cp01780a.

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Anikeenok, O. A., M. A. Augustyniak-Jab?okow, T. A. Ivanova, P. Reiche, R. Uecker e Yu V. Yablokov. "Delocalisation of the Cu2+ Unpaired Electron on the Next Nearest Ligands in LaSrGa0.995Cu0.005O4 Single Crystal". physica status solidi (b) 226, n. 1 (luglio 2001): R1—R3. http://dx.doi.org/10.1002/1521-3951(200107)226:13.0.co;2-r.

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Più fonti

Tesi sul tema "Electronic delocalisation"

Peeks, Martin. "Electronic delocalisation in linear and cyclic porphyrin oligomers". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:58a35932-320c-47dc-828e-0d121d693fd8.

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This thesis presents a combined experimental and computational evaluation of the physical-organic properties of butadiyne-linked porphyrin oligomers. The principal result from the thesis is the synthesis and characterisation of the largest aromatic and antiaromatic systems to date, in the form of an oxidised [6]-porphyrin nanoring, with diameter 2.4 nm. This large electronically coherent system provides insight into the connection between aromatic ring currents and persistent currents in metal and semiconductor mesoscopic rings. Chapter 1 briefly reviews the concepts used in the remainder of the thesis, with a particular focus on aromaticity. In Chapter 2, the barrier to inter-porphyrin torsional rotation in a butadiyne-linked porphyrin dimer is determined computationally and experimentally to be 3 kJ mol^-1. The barrier height is closely related to the resonance delocalisation energy between the porphyrin subunits. In Chapter 3 we show that by oxidising a butadiyne-linked [6]-porphyrin nanoring to its 4+ and 6+ oxidation states, the nanoring becomes antiaromatic and aromatic respectively. In contrast, the neutral oxidation state exhibits only local aromaticity for the six porphyrin units. The 12+ cation can also be generated, and exhibits local antiaromaticity for each porphyrin unit. The characterisation of (anti)aromaticity employs NMR and computational techniques. In Chapter 4, the properties of cation radicals of linear and cyclic porphyrin oligomers are explored. Cations generated by spectroelectrochemistry are measured by optical spectroscopies, and chemically generated radical monocations are examined by cw/pulsed EPR spectroscopies. EPR and optical spectroscopies agree that the dimer monocation radical is fully delocalised, in Robin-Day Class III, whereas the monocations of longer oligomers are localised over 2-3 porphyrin units (Class II). In Chapter 5, photophysical and computational investigations into excited state aromaticity in porphyrin nanorings are presented. The computational results suggest the presence of aromaticity in the triplet excited states, but experiment fails to convincingly demonstrate the effect. Computational results in Chapter 6 show that a butadiyne linked [6]-porphyrin nanoring in which one butadiyne (C≡C-C≡C) is truncated to an alkyne (C≡C) exhibits a reversal of aromaticity and antiaromaticity in its oxidised states, compared to the all-butadiyne linked nanoring, consistent with Hückel's law.

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Li, Junfu. "Correlation of electron delocalisation with pseudocapacitance in nanostructured carbon". Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/53446/.

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The unique electronic structure - partial electron delocalisation (PED) -has been for the first time correlated with pseudocapacitance in graphene-based electrode materials in this study. Pseudocapacitive charge storage was observed on electrodes fabricated from graphene and related materials with different degrees of electron delocalisation (DED%), including graphene oxide (GO), partially oxidised graphene (POG) and polycrystalline monolayer graphene (PMG). GO working electrodes were electrochemically reduced (ECR) via different potential cycling controls to prepare POGs with different DED%. Raman spectroscopy and X-ray photoelectrons spectroscopy (XPS) were used to qualitatively correlate the DED% with the state of oxidation of GOs. It was found that when the ECR was increased from 0 to 1000 potential cycles, the DED% of GO improved from 12.5% to 60.4%. Electrochemical characterisations were used to monitor the charge storage of ECR-treated GOs, i.e. POGs, in 3.0 M KCl and 1.0 M H2SO4, respectively. Cyclic voltammetry (CV) results showed that as the DED of GO was improved, the specific capacitance (Cm) increased from 0.1 to 38.0 F/g in 3.0 M KCl and 0.2 to 62.0 F/g in 1.0 M H2SO4. Electrochemical impedance spectroscopy (EIS) indicated that the improvement of charge storage could be mainly attributed to pseudocapacitance. In the case of PMG, the CV results showed that the value of Cm was ca. 28.0 F/g in 3.0 M KCl and ca. 64.0 F/g in 3.0 M HCl, respectively, although the DED% of PMG was almost 95.0% as derived from the XPS results. The EIS analyses again indicated that the pseudocapacitive contribution predominated the total charge storage. The electronic structures of representative GO models with DED% varying from 0 to 100% were established based on the density functional theory (DFT) modelling. The results showed that extra electronic states only emerged around the Fermi level of POG species (0% < DED% < 100%), but not in fully oxidised graphene (DED% = 0%), nor in pure graphene (DED% = 100%). These states should have originated from the partially delocalised valence electrons rather than those localised electrons. A non-linear relationship between the charge storage capacity and the DED% was found with a peak at between 65.0 and 75.0% of the DED. Finally, by sorting the specific capacitance of the above mentioned graphene species in the order of their DED%, a non-linear relationship has been found again with a peak between 65.0 to 75.0% of the DED. Both the experimental observations and theoretical predictions have revealed a consistent correlation between the pseudocapacitance and the DED% in graphene oxide electrode materials.

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Nadurata, Vincent Lorenzo. "Matériaux moléculaires magnétiques à base de chrome et de pyrazine : composés lamellaires ferrimagnétiques et leurs analogues moléculaires". Electronic Thesis or Diss., Bordeaux, 2024. http://www.theses.fr/2024BORD0418.

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L’utilisation de ligands redox-actifs en chimie de coordination a conduit à une multitude de matériaux aux propriétés magnétiques et électroniques exceptionnelles. Dans la recherche de matériaux magnétiques moléculaires légers et multifonctionnels, la pyrazine redox-active s’est révélée être un excellent ligand pontant en raison de sa capacité à faciliter un échange magnétique fort entre les centres métalliques. Dans cette thèse, nous étudions l’échange magnétique dans des matériaux à base de chrome et de pyrazine. Tout d’abord, le chapitre 1 établit le contexte de ce travail, tandis que le chapitre 2 développe une boîte à outils théorique pour la caractérisation électronique des matériaux présentés par la suite. Trois chapitres expérimentaux présentent les principales découvertes de ce travail. Dans une série de composés ferrimagnétiques en couches, nous montrons que les interactions magnétiques intercouches peuvent être modulées en variant la quantité et la nature des espèces intercalées, ce qui conduit à une modulation du champ coercitif et de la température d’ordre (chapitre 3). La modification postsynthétique de ces matériaux peut entraîner des changements encore plus spectaculaires des propriétés magnétiques : la conversion d’un aimant dur en un aimant doux est induite par la coordination d’un ligand axial sur le chrome en géométrie plane carrée (chapitre 4). Enfin, les origines moléculaires des échanges magnétiques forts et de la délocalisation électronique sont étudiées dans un analogue moléculaire miniaturisé portant un seul pont chrome-pyrazine-chrome (chapitre 5). Le chapitre 6 rassemble ces résultats et explore les nombreuses voies que pourraient emprunter de futures recherches basées sur ce travail
The use of redox-active ligands in coordination chemistry has led to a multitude of materials with exceptional magnetic and electronic properties. In the pursuit of lightweight, multifunctional molecule-based magnets, the redox-active pyrazine has emerged as an excellent bridging ligand candidate due to its ability to facilitate strong magnetic exchange between metal centres. In this thesis, we study the magnetic exchange in chromium-pyrazine materials. First, Chapter 1 lays a context for this work, while Chapter 2 develops a theoretical toolbox for the electronic characterisation of the materials presented in the following. Three experimental chapters present the major findings of this work. In a series of layered ferrimagnets, we show that the interlayer magnetic interactions can be tuned by varying the quantity and nature of the intercalated species, leading to a modulation of the coercive field and ordering temperature (Chapter 3). Post-synthetic modification of such materials can lead to even more dramatic changes in the magnetic properties: conversion from a hard to a soft magnet is induced by axial ligand coordination to square-planar chromium (Chapter 4). Finally, the molecular origins of strong magnetic exchange and electronic delocalisation are probed in a miniaturised molecular analogue bearing a single chromium-pyrazine-chromium bridge (Chapter 5). Chapter 6 ties these results together and explores the many avenues which future investigations based on this work may take

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Ichas, Valerie. "Étude sous pression des propriétés électroniques et magnétiques de composés de neptunium : NpGa3 et les monopnictures de Np : Net réalisation d'un réfrigérateur d'3He pour la mesure de la résistance électrique en dessous de 1,5K". Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10041.

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La resistance electrique des monopnictures de neptunium npas, npsb, npbi (structure nacl) et de npga#3 (structure aucu#3) a ete mesuree sous haute pression jusqu'a 25gpa et a basse temperature jusqu'a 1. 5k. Dans les monopnictures de np, la mise en ordre antiferromagnetique triple k (3k) produit une forte augmentation de la resistivite a pression ambiante. De plus, dans npsb et npbi, la resistivite montre un comportement semi-conducteur a basse temperature. Sous pression et dans les trois composes, la temperature d'ordre t#o#r#d diminue et la resistance chute discontinuement a basse temperature. La signature de l'ordre 3k est supprimee dans npas et npsb. L'anomalie kondo de la resistance disparait sous pression. La chute de resistance sous pression est interpretee par une modification de la surface de fermi qui coincide probablement avec la suppression de la phase 3k. Nous suggerons que la diminution de t#o#r#d est due a un changement de la surface de fermi en plus d'une legere delocalisation des electrons 5f. Dans npga#3, t#o#r#d augmente de 65k a 1bar jusqu'a 194k a 25gpa. L'anomalie kondo en resistivite est supprimee au dessus de 4gpa. Nos resultats suggerent que deux phases magnetiques sont presentes sous pression. Le comportement sous pression du moment ordonne et de la temperature d'ordre indique une faible delocalisation des electrons 5f. L'augmentation de la temperature d'ordre est expliquee par le renforcement des interactions d'echange indirectes entre ions magnetiques. Parallelement, nous avons developpe un prototype d'un refrigerateur #3he avec pompe a absorbtion par des charbons actifs. Il est destine a mesurer la resistance electrique de composes d'actinides en dessous de 1. 5k et sous haute pression. Le prototype permet d'atteindre des temperatures minimales de 650mk dans les conditions de mesures sous pression et 330mk dans les conditions de mesures a 1bar. Nous avons mesure avec succes la resistance electrique de np#4ru#7ge#6 jusqu'a 350mk et a pression ambiante

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Mougenot, Pierre. "Etude theorique ab initio scf et ci de complexes organometalliques binucleaires". Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13025.

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Analyse approfondie du spectre photoelectronique se(fe(c::(5)h::(5)))::(2)(no)::(2). Etude critique des resultats experimentaux anterieurs concernant le diamagnetisme suppose se(co(c::(5)h::(5)))::(2)(no)::(2). Bon accord avec l'experience dans l'etude theorique de l'etat fondamental du cation dirhodium tetraacetate dihydrate. Etude sur la nature de l'interaction metal-metal dans (v(c::(5)h::(5)))::(2) (c::(8)h::(8))

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Perrin, Éric. "Contribution a l'interpretation des proprietes vibrationnelles du polyacetylene et de certains polymeres conjugues". Nantes, 1988. http://www.theses.fr/1988NANT2007.

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Etude vibrationnelle experimentale et theorique de plusieurs polymeres conducteurs. Les resultats obtenus sur du polyacetylene oriente confirment le modele de distribution bimodale de segments conjugues. Etude de l'effet de conjugaison sur le polyacetylene pur et dope (fecl::(4)**(-)) et sur le polyphenylene-vinylene

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Capitoli di libri sul tema "Electronic delocalisation"

Benedict, U., J. P. Itié, C. Dufour, S. Dabos e J. C. Spirlet. "Delocalisation of 5f Electrons in Americium Metal under Pressure: Recent Results and Comparison with other Actinides". In Americium and Curium Chemistry and Technology, 213–24. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5444-1_16.

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Michael, Hornby, e Peach Josephine. "Acids and bases". In Foundations of Organic Chemistry: Worked Examples. Oxford University Press, 2000. http://dx.doi.org/10.1093/hesc/9780198505839.003.0003.

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This chapter discusses equilibria and factors effecting acidity and basicity of organic compounds and other areas of chemistry, such as electronegativity of the atom that bear the charge. It examines delocalization, resonance, inductive effects, indicators, and interactions between molecules and ions. It also deals with the protonation on the carbonyl oxygen atom that gives the more stable, delocalized protonated form of the COOH group. The chapter mentions the inductive electron-withdrawing effect of the C=O that helps to weaken the adjacent O-H bond and carboxylic acids that are more acidic than alcohols, whose anions are not stabilized by delocalisation. It refers to Tenormin, which is a drug used in the treatment of high blood pressure, angina, and abnormal heart rhythms.

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Inkpen, Michael S., e Nicholas J. Long*. "Metal σ-Alkynyl Complexes as Molecular Wires and Devices: A Comparative Study of Electron Density and Delocalisation". In Molecular Design and Applications of Photofunctional Polymers and Materials, 85–129. The Royal Society of Chemistry, 2012. http://dx.doi.org/10.1039/9781849735759-00085.

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Atti di convegni sul tema "Electronic delocalisation"

Balzer, Daniel, e Ivan Kassal. "The Decisive Role of Carrier Delocalisation in Organic Electronics". In 13th Conference on Hybrid and Organic Photovoltaics. València: Fundació Scito, 2021. http://dx.doi.org/10.29363/nanoge.hopv.2021.068.

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Verbandt, Y., H. Thienpont, I. Veretennicoff e G. L. J. A. Rikken. "A Simple Quasi-free Electron Model for the Description of Linear and Nonlinear Optical Properties of Conjugated Oligomers : A Focus on Length Dependence, Monomer Anharmonicity and Delocalisation." In Organic Thin Films for Photonic Applications. Washington, D.C.: Optica Publishing Group, 1993. http://dx.doi.org/10.1364/otfa.1993.wd.20.

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Conjugated molecules are very promising organic materials for nonlinear optics applications. It has been established that the linear and nonlinear properties of this class of molecules scale in a nonlinear way with respect to the π-electron delocalisation length along the conjugated backbone. Some systematic experimental investigations on the length dependence of the molecular optical response of thiophene and phenyl oligomers have been published [1,2]. Thienpont et al. [1] found a saturation of the polarizability α and the second hyperpolarizability γ at about 7 repeat units. We use the term saturation point to denote the transition point where the scaling of the optical properties with the molecular length becomes linear.

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Pastor, Ernest, e Artem Bakulin. "Ultrafast Electron Localisation and Delocalisation in Photoelectrochemical Cells. Towards Control of Excited-State Transport". In nanoGe Fall Meeting 2018. València: Fundació Scito, 2018. http://dx.doi.org/10.29363/nanoge.fallmeeting.2018.235.

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