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We have calculated the current density induced by an external magnetic field in a set of figure-eight-shaped expanded porphyrinoids. The studied octaphyrins can be divided into three classes (N2, N4, and N6) based on the number of the inner hydrogen atoms of the pyrrole rings. Using the Runge-Kutta method, the current density is split into diatropic and paratropic contributions that are analyzed separately. The calculations show that one common ring current consists of two rather independent pathways. Each of them follows the outer side of the molecular frame of one half of the molecule and passes to the inner side of the frame on the other half. The ring-current pathways are similar to the ones for [12]infinitene. However, the current density of the octaphyrins is though more complex having many branching points and pathways. Vertical through-space current-density pathways pass in the middle of the molecules through a plane that is parallel to the figure-eight-shaped view of the molecules when the magnetic field is perpendicular to the plane. The isolectronic N2 and the N4 dication sustain a weak paratropic ring current inside the molecule, which is also observed in the 1H NMR magnetic shielding constant of the inner hydrogen atoms. The diatropic current-density contribution dominates in the studied molecules. For the N4 and N6 molecules, the global current-density pathways are only diatropic and N6 sustains the strongest global diatropic current-density flux of 13.2 nA/T. We have calculated the current density induced by an external magnetic field in a set of figure-eight-shaped expanded porphyrinoids. The studied octaphyrins can be divided into three classes (N2, N4, and N6) based on the number of the inner hydrogen atoms of the pyrrole rings. Using the Runge-Kutta method, the current density is split into diatropic and paratropic contributions that are analyzed separately. The calculations show that one common ring current consists of two rather independent pathways. Each of them follows the outer side of the molecular frame of one half of the molecule and passes to the inner side of the frame on the other half. The ring-current pathways are similar to the ones for [12]infinitene. However, the current density of the octaphyrins is more complex having many branching points and pathways. Vertical through-space current-density pathways pass in the middle of the molecules through a plane that is parallel to the figure-eight-shaped view of the molecules when the magnetic field is perpendicular to the plane. The isolectronic N2 and the N4 dication sustain a weak paratropic ring current inside the molecule, which is also observed in the H-1 NMR magnetic shielding constant of the inner hydrogen atoms. The diatropic current-density contribution dominates in the studied molecules. For the N4 and N6 molecules, the global current-density pathways are only diatropic and N6 sustains the strongest global diatropic current-density flux of 13.2 nA T-1.

Benziporphyrins are versatile macrocycles exhibiting aromaticity switching behaviors. The existence of both Hückel and Möbius (anti)aromaticity has been reported in these systems, whose validity is respectively governed by the [4n + 2] and [4n] π-electron rule on the macrocyclic pathway. Despite the experimental evidence on the floppiness of benziporphyrins, the switching mechanism between Hückel and Möbius structures is still not clear, as well as the factors influencing the stability of the different π-conjugation topologies. For these reasons, we performed a systematic study on A,D-di-p-benzihexaphyrins(1.1.1.1.1.1) with two redox states corresponding to [28] and [30] π-electron conjugation pathways. Whereas benzi[28]hexaphyrin obeys Möbius aromaticity, benzi[30]hexaphyrin follows Hückel aromaticity. The dynamic interconversion between Möbius and Hückel aromaticity is investigated through the rotation of a phenylene ring, which acts as the topology selector. Further analyses of the energy profiles using energy decomposition and information-theoretic approaches provide new insights into conformational stability, aromaticity and antiaromaticity for these species. Strong and opposite cross correlations between aromaticity indexes and information-theoretic quantities were found for the two macrocyclic systems with opposite global aromaticity and antiaromaticity behaviors. These results indicate that Hückel and Möbius aromaticity and antiaromaticity, though qualitatively different, are closely related and can be interchanged, and information-theoretic quantities provide a novel understanding about their relevance. Our present results should provide in-depth insights to appreciate the nature and origin about Möbius (anti)aromaticity and its close relationship with Hückel (anti)aromaticity.

This essay describes the successive births of valence bond (VB) theory during 1916–1931. The alternative molecular orbital (MO) theory was born in the late 1920s. The presence of two seemingly different descriptions of molecules by the two theories led to struggles between the main proponents, Linus Pauling and Robert Mulliken, and their supporters. Until the 1950s, VB theory was dominant, and then it was eclipsed by MO theory. The struggles will be discussed, as well as the new dawn of VB theory, and its future.

In this study, we investigate the effects of nitrogen and boron dopants on the properties of phenalene/phenalenyl systems based on the Hückel theory by using the Hueckel Molecular Orbital software. The dopants configurations are graphitic, pyridinic, and pyrrolic. The electronic configuration of bare phenalene confirms the delocalization of π electrons and the radical properties of the molecule, which is in good agreement with the results of previous studies. Dopant types and positions strongly affect the number of π electrons in the system, molecular orbital energy, total energy, average π-electron energy, and gap energy. The molecular energy level degeneracy strongly depends on the rotational symmetry of the system, in the order of graphitic, pyridinic, and pyrrolic. A preserved radical behavior and the number of π electrons are found for the pyridinic dopant type, while closed electronic configuration is observed for graphitic and pyrrolic types. A lower gap energy is typically found for B-doped phenalene compared to that for N-doped phenalene; this opens the possibility for the enhancement of photoluminescence intensity. This study, although qualitative, confirms the effects of dopants on the chemical and physical properties of phenalene/phenalenyl systems.

The topology of twisted molecular rings is characterized by the linking number, which is equal to the sum of the twist-a local property of the molecular frame-and the writhe-a global parameter, which represents the bending of the molecular ring. In this work, we investigate a number of cyclic all-trans C40H40 annulenes with varying twisting numbers for a given linking number and their dications. The aromatic character is assessed by calculating ring-current strength susceptibilities using the gauge-including magnetically induced currents (GIMIC) method, which makes it possible to conduct a systematic study of the relation between the topology and aromaticity of twisted molecules. We found that the aromatic properties of the investigated Mobius twisted molecules are not only dependent on the linking number as previously suggested but also depend strongly on the partitioning of the linking number into the twist and writhe contributions.

Submitted by Angela Maria de Oliveira (amolivei@uepg.br) on 2017-10-25T13:39:14Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Januario Kordiak.pdf: 1907122 bytes, checksum: a65c6272637170bbfa2b17ce2175c777 (MD5) Made available in DSpace on 2017-10-25T13:39:14Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Januario Kordiak.pdf: 1907122 bytes, checksum: a65c6272637170bbfa2b17ce2175c777 (MD5) Previous issue date: 2017-08-25 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior O ensino de ligações químicas é uma das fases mais importantes no processo de ensino-aprendizagem da Química. Todavia, existe uma grande necessidade de introduzir aos educandos do Ensino Médio a conexão entre a ligação química e a sua natureza quântica. Para alcançar esse objetivo utilizou-se o método de Hückel, um método simples desenvolvido em pesquisas em Química Teórica, antes do início da química computacional. Como metodologia avaliativa o método foi contraposto com as concepções prévias e posteriores dos educandos e, separadamente, com as concepções de educandos ensinados pelo método tradicional, ou seja, quadro, giz e livro. Foi observado que o uso de conceitos atuais, principalmente com o uso do computador, melhorou as argumentações por parte dos educandos ao definirem as ligações químicas, indicando que as aplicações da química quântica aliada a programas computacionais contribuem para resultados expressivos no processo de ensino-aprendizagem da Química. The nature of chemical bond is essential to understand chemistry concepts, mainly, at initial process in high school. From quantum mechanics concepts was possible describe the chemical bond basing in electronic density, which around the nucleus between two atoms. Hückel method was the first method presented to solve the Schrodinger Equation in approximate level and it reached good qualitative results for aromatic compounds indicating the feasibility of the computational chemistry. However, the Hückel method based on matrix is in accordance with molecular geometry proposed; then, the resolution of such method is possible for students in high level. From this idea, we presented the Hückel method as fundamental to understand the chemical bond for students in the first and second years of high school and we applied questions to evaluate the chemical bond knowledge before/after the Hückel method. We observed that there was increase and reinforce of the chemical bond concept for students.

Meso‐aryl expanded porphyrins present a structural versatility that allows them to achieve different topologies with distinct aromaticities. Several studies appeared in the literature studying these topological switches from an experimental and theoretical point of view. Most of these publications include density functional theory calculations, being the B3LYP the most used methodology. In this work, we show that the selection of the functional has a critical role on the geometric, energetic, and magnetic results of these expanded porphyrins, and that the use of an inadequate methodology can even generate spurious stationary points on the potential energy surface. To illustrate these aspects, in this article we have studied different molecular distortions of two expanded porphyrins, [32]‐heptaphyrin and [26]‐hexaphyrin using 11 DFT functionals and performing single point energy calculations at the local pair natural orbital coupled cluster DLPNO‐CCSD(T) method, which have been carried out for benchmarking purposes. For some selected functionals, the dispersion effects have also been evaluated using the D3‐Grimme's dispersion correction with Becke–Johnson damping. Our results let us to conclude that the CAM‐B3LYP, M05‐2X, and M06‐2X functionals are the methodologies that provide a more consistent description of these topological switches, while other methods, such as B3LYP, BPE, and BP86, show a biased description., Ministerio de Economía y Competitividad of Spain . Grant Numbers: CTQ2016‐80375‐P , CTQ2014‐52525‐P , CTQ2014‐51912‐REDC -Universidad del País Vasco ‐ Euskal Herriko Unibertsitatea (UPV/EHU) . Grant Number: UFI11/22 QOSYC -Basque Government . Grant Number: IT673‐13 -Generalitat de Catalunya . Grant Number: 2014SGR139

International audience; The HuLiS program is presented as a tool to decompose a delocalized wave function as a linear combination of localized electronic structures. The principles of the energy based HL-CI and the overlap based schemes HL-P are developed. The results obtained for a set of 10 relevant organic molecules are shown to compare very well with high level quantum chemistry calculations. A trust factor τ is introduced and its use is shown on the allyl radical case where symmetry must be taken into account.

International audience; The introduction of computational chemistry experiments for undergraduate students in sciences can really facilitate knowledge acquisition. It can make consistent various concepts in chemistry without a lengthy experimental protocol involving synthesis and physical chemistry mesurements. In the present case the students use a very simple molecular modeling program that we implemented: HuLiS. The computational chemistry experiment described herein is devoted to an important concept in chemistry: resonance between Lewis structures (mesomerism). In this context, conjugated ring species, as herein, are somewhat specific in the sense that aromaticity can play an important role. Hence, we discuss here a rather advanced resonance effect, where the usual qualitative rules do not suffice by themselves, but aromaticity and the ―4n+2 electron‖ rule must be considered. This Hückel rule can be numerically displayed with an appropriate computational experiment. We use our free java applet (HuLiS) designed to evaluate the weights of resonance structures. As it is based on Hückel theory, the computations are fast, and the theoretical background is much simpler than with ab initio programs, hence the teachers are likely to master the tool used by the students. Upon substitutions, the weights of the zwitterionic Lewis structures adapt to the electronegativity. This is an opportunity to discuss the role of electronegativity in mesomerism, and strengthen the knowledge of the students.

Trois thèmes de recherche sont présentés dans ce travail.Les pseudo potentiels moléculaires développés dans le cadre de ce travail sont des potentiels développé&s pour des atomes hybridés. Le cas de l'atome de carbone sp2 est développé, que ce soit pour l'atome seul ou pour l'atome en interaction avec d’autres atomes portant ou non des pseudo potentiels. Grâce à ce travail, il est possible de reproduire avec précision la spectroscopie de polyènes, d'hydrocarbures polycycliques aromatiques et de molécules plus petites mais plus complexes. Finalement, un pseudo potentiel est développé pour un pseudo atome lié par une vrai liaison sigma.Le second thème de recherche est le développement de l'application HuLiS qui permet de développer une structure électronique délocalisée (par exemple une solution obtenue par la méthode de Hückel) sur une base de structures localisées, quelles soient de Lewis et/ou de Valence Bond.Enfin, une application de chimie théorique est présentée. Il s'agit d'une interaction avec deux groupes d'expérimentateurs qui a permis de comprendre pour quoi le trans-1,2-disiloxybenzocyclobutène capture le dioxygène triplet alors que cette réaction est interdite de spin.

The electronic structure of finite and infinite linear, cyclic, and Möbius strip polyacenes has been investigated by adopting simple Hückel methodology without and with variable β resonance integrals and the more involved MNDO scheme. Using the Hückel approach, it turns out that the linear polyacenes and the Möbius ladder molecules exhibit HOMO-LUMO gap which monotonously decrease with chain length while their cyclic analogs have a sawtooth behavior. The originality of the approach is to combine band structure and MO approaches to get analytical forms of the energy levels. These results are corroborated at the MNDO levels where the geometry relaxation effects are taken into account. The optimized MNDO structures show that the Möbius defect is localized and extends over approximately one-third of the ladder. Accounting for geometry distortion at the MNDO level results in an increase of the gap of the Möbius strip relative to the linear and cyclic finite size structures, but the similar results for the two methods confirm that the topology is the main factor acting on HOMO-LUMO energy gaps.

Große flexible Moleküle, wie z.B. Proteine, Kohlenhydrate und andere Naturstoffe besitzen viele Freiheitsgrade und es ist in der Regel schwierig, die stabilsten und damit biochemisch wichtigen Konformationen und deren Umwandlungspfade zu finden. Ein sehr häufig verwendetes Verfahren um die Konformationsräume solcher molekularen Systeme theoretisch zu untersuchen ist die Moleküldynamik (MD). Nachteil dieses Verfahrens ist, dass eine grosse Menge Daten erzeugt wird, die hochredundant und multidimensional sind. In der vorliegenden Arbeit wird zum ersten Mal der Ansatz verfolgt, diese Daten mithilfe eines künstlichen, neuronalen Netzes vom Kohonen-Typ (welches der Hirnfunktion des visuellen Kortex ähnelt) zu untersuchen. Dabei werden zweidimensionale Karten der Konformationshyperfläche des Systems erhalten, die ähnlich wie topologische Landkarten, konformative Minima und deren Verbindungswege visuell anschaulich zeigen. Die räumliche Struktur beeinflusst auch wichtige Moleküleigenschaften, wie z.B. die Aromatizität in cyclisch konjugierten Ringen (Annulenen). 1964 hatte der theoretische Chemiker E. Heilbronner vorhergesagt, dass Annulene, die in sich um 180° verdrillt sind, d.h. eine Möbius-Topologie besitzen mit 4n Elektronen aromatisch sind und damit gegen die Hückel-(4n+2)-Regel verstoßen. Trotz zahlreicher Versuche konnte bis vor kurzem kein experimenteller Nachweis für diese Hypothese gefunden werden. Größere Annulen-Ringe besitzen sehr viele mögliche Konformationen und Konfigurationen (z.B. [30]Annulen : 17920860). Um die Möbius-Nadeln im „Annulen-Heuhaufen" zu finden wurde ein Programm entwickelt, welches automatisch Isomere der Annulene generiert und auf Möbius-Topologie und Aromatizität untersucht. Unter einigen Annulenen wurden in der Tat stabile Möbius-Isomere gefunden, die möglicherweise interessante Syntheseziele darstellen. Der Arbeit liegt eine DVD mit Programmen und Beispieldaten bei. Diese ist auf Anfrage auch beim Autor erhältlich. Large and flexible molecules, like proteins, carbohydrates and other natural products exhibit numerous degrees of freedom. It is generally quite difficult to find the most stable, and biochemically most active conformations and their paths of interconversion. Application of Molecular Dynamics (MD) has been established as one of the most important theoretical techniques to study the conformational space of these molecular systems. The sheer amount of highly redundant and multidimensional data produced by MD calculations constitutes a key problem of this method. This thesis will present the first application of artificial neural networks of the Kohonen type (which closely resemble the organization of the visual cortex) to investigate this wealth of data. Thus, two-dimensional representations of the conformational hypersurface are obtained, which, like topological maps, visualize conformational minima and interconversion pathways in an intuitive way. The three-dimensional molecular structure also influences important molecular properties, such as the aromaticity in cyclic, conjugated rings (annulenes). 1964 the theoretical chemist E. Heilbronner suggested that annulenes, which are twisted in themselves by 180° in a Möbius topology, should be aromatic with 4n electrons, thus, breaking the Hückel (4n+2)-rule. Despite of numerous attempts, until very recently no experimental proof of this hypothesis was found. For large annulenes, a numerous conformations and configurations exist (e.g. [30]annulene). To find the "Möbius needles" in the "annulene haystack" an algorithm was developed and implemented in a program which automatically generates isomers and analyses them for Möbius topology and aromaticity. Indeed, several stable Möbius isomers have been discovered which can be considered as interesting synthetic targets.

Rapporteurs: M. Jean-François HALET, directeur de recherche CNRS, LCSIM, Rennes M. Jean-Paul ITIE, directeur de recherche CNRS, LPMC, Paris. Examinateurs: M. Michel EVAIN, professeur, Université de Nantes M. Stéphane JOBIC, chargé de recherhe CNRS, IMN, Nantes M. Mohamed MEZOUAR, responsable scientifique, ESRF, Grenoble M. Guy OUVRARD, professeur, Université de Nantes Invité : Mme Graziella GOGLIO, maître de conférence, ICMCB, Bordeaux; This thesis deals with the analysis of the electronic structure of dichalcogenides of platinum and palladium, solid state compounds which adopt peculiar structural arrangements. A preliminary study at ambient pressure is realized on the PtQ2 (Q = O, S, Se, Te) family which adopts the polymeric CdI2 type structure with a low c/a ratio. Thanks to ab initio calculations, we are able to identify the factors responsible for this value. An electronic transfer from anionic to cationic bands leads to a decrease of the c parameter while orbital and geometric factors induce the increase of the a parameter. Then, PtO2, only stable lamellar oxide, was examined. We show that the electronic count is responsible for the structural arrangement. The partial electronic transfer for PtTe2 shows that the chalcogenides charge balance has to be redefined. The strong combination between p and d orbitals, evidenced by calculations, prevents us to determine a charge balance for PtTe2 and PdTe2 which can be written Pt3+(Te-1,5)2 and Pd2+(Te-1)2 atr ambient pressure. In the case of PtTe2, high pressure does not induce an electronic transfer but a rearrangement. The same phenomenon is observed for PdSe2. This compound undergoes a phase transition from the PdS2- to the pyrite-type structure without electronic transfer but with a cooperative Jahn-Teller distorsion. The influence of temperature was finally studied and shows strong structural rearrangements in the pyrite-type structure.; Les travaux rassemblés dans cette thèse concernent l'analyse des structures électroniques de dichalcogénures de platine et de palladium, composés solides présentant pour certains des anomalies structurales. Une étude préalable à pression ambiante est réalisée sur la famille PtQ2 (Q = O, S, Se et Te). Les quatre composés adoptent un type CdI2 polymère avec un rapport c/a très faible. A l'aide de calculs quantiques (méthodes DFT et EHTB), les phénomènes responsables sont identifiés. Un transfert électronique des anions chalcogénures vers le platine entraîne la diminution du paramètre c, tandis que des facteurs orbitalaires et géométriques provoquent l'augmentation du paramètre a. Un accent particulier est mis sur l'étude de PtO2, seul oxyde lamellaire stable. Des calculs quantiques montrent que c'est le décompte électronique qui gouverne l'arrangement structural. Le remplissage partiel des bandes d(Pt) et sp(Te) pour PtTe2 pose la question de l'équilibre des charges réel dans les chalcogénures. Pour y répondre, l'outil haute pression a été utilisé dans les cas de PtTe2, PdTe2 et PdSe2. Une analyse des distances, couplée avec des calculs DFT, montre que les formulations Pt3+(Te-1,5)2 et Pd2+(Te-1)2 semblent convenir à pression ambiante. Une très forte combinaison entre orbitales p(Q) et d(M) est constatée, empêchant l'établissement clair d'un équilibre des charges. Des expériences de synthèse et de caractérisation structurale par diffraction des rayons X mettent en évidence l'absence de transition de phase pour ces ditellurures. Dans le cas de PtTe2, l'application de pression ne conduit pas à un transfert de charges mais à un réarrangement électronique. Le composé PdSe2 subit quant à lui une transition de phase vers le type pyrite par diminution des distances Pd-Se interfeuillet. Encore une fois, il n'y a pas de transfert électronique mais un réarrangement correspondant à une distorsion Jahn-Teller coopérative. L'influence de la température est ensuite étudiée et montre des réarrangements structuraux très importants dans le type pyrite.