Dissertations / Theses: 'Conjugated and cumulated molecules' – Grafiati (2024)

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In dieser Dissertation wird die Selbstorganisation von pi-konjugierten (makro)molekularen Architekturen durch Chemisorption oder Physisorption in hochgeordnete supramolekulare nanoskopische und mikroskopische Strukturen auf festen Trägern untersucht. Ihre Struktur und Dynamik wurden auf molekularer Skala hauptsächlich mit Rastersondenmikroskopien, insbesondere mit Rastertunnel- und Rasterkraftmikroskopie, untersucht. Dies erlaubte die Charakterisierung einer Reihe von Phänomenen, die sowohl an Fest-Flüssig-Grenzflächen auftreten, wie beispielsweise die Dynamik der einzelnen molekularen Nanostäbchen (Ostwald Reifung) und die Fraktionierung steifer Polymerstäbchen durch Physisorption an der Grafitoberfläche aus der Lösung heraus, als auch in trockenen Filmen vorkommen wie die Selbstorganisation steifer Polymerstäbchen zu Nanobändern mit molekularen Querschnitten, die sich epitaktisch auf Oberflächen orientieren lassen und auch die Ausbildung gestapelter Architekturen von diskförmigen Molekülen. Außerdem wurden die elektronischen Eigenschaften der untersuchten Systeme mit Hilfe von Photoelektronenspektroskopie charakterisiert. Die entwickelten Nanostrukturen sind nicht nur für Nanokonstruktionen auf festen Oberflächen von Interesse, sondern besitzen auch Eigenschaften, die sie für Anwendungen in einer zukünftigen molekularen Elektronik prädestiniert, etwa für den Aufbau molekularer Drähte.
In this thesis the self-assembly of pi-conjugated (macro)molecular architectures, either through chemisorption or via physisorption, into highly ordered supramolecular nanoscopic and microscopic structures has been studied. On solid substrates structure and dynamics has been investigated on the molecular scale making use primarily of Scanning Probe Microscopies, in particular Scanning Tunneling Microscopy and Scanning Force Microscopy. This allowed to characterize a variety of phenomena occurring both at the solid-liquid interface, such as the dynamics of the single molecular nanorods (known as Ostwald ripening), the fractionation of a solution of rigid-rod polymers upon physisorption on graphite; and in dry films, i.e. the self-assembly of rigid-rod polymers into nanoribbons with molecular cross sections which can be epitaxially oriented at surfaces and the formation ordered layered architectures of disc-like molecules. In addition the electronic properties of the investigated moieties have been studied by means of Photoelectron Spectroscopies. The nanostructures that have been developed are not only of interest for nanoconstructions on solid surfaces, but also exhibit properties that render them candidates for applications in the field of molecular electronics, in particular for building molecular nanowire devices.

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In this thesis, we present a study of conformational disorder in conjugated molecules focussed primarily on molecular dynamics (MD) simulation methods. Along with quantum chemical approaches, we develop and utilise MD simulation methods to study the conformational dynamics of polyfluorenes and polythiophenes and the role of conformational disorder on the optical absorption behaviour observed in these molecules. We first report a classical force-field parameterisation scheme for conjugated molecules which defines a density functional theory method of accuracy comparable to high-order ab-initio calculations. In doing so, we illustrate the role of increasing conjugated backbone and alkyl side-chain length on inter-monomer dihedral angle potentials and atomic partial charge distributions. The scheme we develop forms a minimal route to conjugated force-field parameterisation without substantial loss of accuracy. We then present a validation of our force-field parameterisation scheme based on self-consistent measures, such as dihedral angle distributions, and experimental measures, such as persistence lengths, obtained from MD simulations. We have subsequently utilised MD simulations to investigate the interplay of solvent and increasing side-chain lengths, the emergence of conjugation breaks, and the wormlike chain nature of conjugated oligomers. By utilising MD simulation geometries as input for quantum chemical calculations, we have investigated the role of conformational disorder on absorption spectral broadening and the formation of localised excitations. We conclude that conformational broadening is effectively independent of backbone length due to a reduction in the effect of individual dihedral angles with increasing length and also show that excitation localisation occurs as a result of large dihedral angles and molecular asymmetry.

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Die Verwendung einzelner Moleküle als aktive Elemente elektronischer Bauteile wird derzeit als potentielle Alternative zur halbleiterbasierten Nanoelektronik angesehen, da einzelne Moleküle a priori nur einige Nanometer groß sind. Auß erdem kann dabei eventuell eine vereinfachte Verarbeitung und Herstellung der Bauteile erreicht werden. In dieser Arbeit werden das Selbstaggregationsverhalten und die Elektrontransporteigenschaften konjugierter Moleküle mit Rastertunnelmikroskopie (RTM) und -spektroskopie (RTS) an einer Fest-Flüssig-Grenzfläche und unter Ultrahochvakuumbedingungen bei tiefen Temperaturen untersucht. Ihre mögliche Verwendung in hybrid-molekularen Bauteilen als auch Ansätze für eine mono-molekulare Elektronik werden erkundet. Insbesondere wird die Nano-Phasenseparation von Elektron-Donor-Akzeptor-Multiaden an der Fest-Flüssig-Grenzfläche demonstriert, die zur Integration verschiedener elektronischer Funktionen auf der Nanoskala benutzt werden kann. Desweiteren wird die Abhängigkeit der elektronischen Kopplung scheibenförmiger gestapelter Moleküle vom lateralen Versatz innerhalb des Stapels experimentell nachgewiesen. Dies eröffnet neue Möglichkeiten die elektronischen Eigenschaften solcher dreidimensionaler Architekturen gezielt zu beeinflussen. Außerdem werden die ersten RTM/RTS-Untersuchungen von Ladungstransferprozessen in einzelnen organischer Donor-Akzeptor-Komplexe präsentiert. Schließlich werden die Ladungstransferkomplexe mit dem Ansatz der Nano-Phasenseparation kombiniert, um den ersten Einzelmolekültransistor mit intergrierten Nanogates zu realisieren. In diesem prototypischen Bauteil wird die Strom-Spannungs-Kennlinie einer hybrid-molekularen Diode, die aus einem Hexa-peri-hexabenzocoronen (HBC) im Tunnelspalt eines RTMs besteht, durch einen kovalent an das HBC gebundenen Ladungstransferkomplex modifiziert. Dies wird als wichtiger Schritt in Richtung einer mono-molekularen Elektronik angesehen.
The use of single molecules as active components in electronic devices is presently considered a potential alternative to semiconductor-based nano-scale electronics since it directly provides precisely-defined nano-scale components for electronic devices which eventually allows for simple processing and devicefabrication. In this thesis the self-assembly and electron transport properties of conjugated molecules are investigated by means of scanning tunneling microscopy (STM) and spectroscopy (STS) at solid-liquid interfaces and under ultrahigh vacuum conditions and low temperatures. The use of the molecules in hybrid-molecular electronic devices and potential approaches to a mono-molecular electronics are explored. In particular, electron-donor-acceptor-multiads are shown to exhibit a nano-phase-segregation at the solid-liquid interface which allows for the integration of different electronic functions at the nano-scale. Furthermore, the dependence of the electronic coupling of stacked disk-like molecules on the lateral off-set in the stack is demonstrated experimentally which offers new possibilities for the control of the electronic properties of these three-dimensional architectures. In addition the first STM/STS experiments on charge transfer in single organic donor-acceptor complexes are presented. Finally, charge transfer complexes are combined with the approach of nano-phase-segregation to realize the first single-molecule transistor with integrated nanometer-sized gates. In this prototypical device the current through a hybrid-molecular diode made from a hexa-peri-hexabenzocoronene (HBC) in the junction of the STM is modified by charge transfer complexes covalently attached to the HBC in the gap. Since the donor which complexes the covalently attached acceptor comes from the ambient fluid the set-up represents a single-molecule chemical field-effect transistor with nanometer-sized gates. This is considered a major step towards mono-molecular electronics.

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In dieser Arbeit wird die Phasenseparation und Mischung zwischen konjugierten Stäb-chenmolekülen in dünnen Filmen untersucht. Hauptaugenmerk liegt darauf zu ergrün-den welche molekularen Eigenschaften zu Mischung und/ oder Phasenseparation füh-ren. Mit den 5 Molekülen Pentacen (PEN), Quaterthiophen (4T), Sexithiophen (6T), p-Sexiphenylen (6P), alpha,omega-Dihexylsexithiophen (DH6T) werden Materialpaare zusammen gestellt, die sich in den Parametern „optische und elektrische Eigenschaf-ten“, „Länge des konjugierten Kerns“ und Alkylkettensubstitution unterscheiden. Alle Schichten werden mittels organischer Molekularstrahlabscheidung auf die Substrate Siliziumoxid und Mylar, einer PET Folie, simultan von zwei Quellen aufgedampft. Das Mischungsverhältnis wird mittels der individuellen Aufdampfraten eingestellt und eine Gesamtrate von 0.5 nm/min eingehalten. Es wird Phasenseparation für Materialpaare mit ungleicher konjugierter Kernlänge, z.B. [4T/6T], beobachtet. Erstaunlicherweise führt die Co-Verdampfung von Molekülpaaren mit ähnlicher konjugierter Kernlänge [4T/PEN] und [6T/6P] zu wohlgeordneten Fil-men, in denen die Moleküle in gemischten Lagen parallel zur Substratoberfläche auf-wachsen und die Längsachse der Moleküle fast senkrecht zur Substratoberfläche orien-tiert ist. Molekülpaare mit ähnlicher konjugierter Kernlänge und Alkylsubstitution [6T/DH6T] und [6P/DH6T] zeigten ebenfalls geordneten Schichten, wobei als Besonderheit eine lineare Abhängigkeit des Lagenabstandes vom DH6T-Gehalt zu beobachten ist. Dies wird mit einer Phasenseparation in eine aromatische und eine alkyl Domäne erklärt. Mit abnehmendem DH6T-Gehalt im Film ist die Alkyldomäne weniger dicht gepackt, was auf Grund der Flexibilität der Alkylketten zu einer Abnahme des gesamten Lagenab-standes führt. Die besonders geringe Oberflächenrauhigkeit und die miteinander verbundenen Inseln der [DH6T/6T] Filme prädestinieren sie zur Verwendung in Feldeffekttransistoren. Es wird gezeigt, dass es möglich ist, die Ladungsträgerdichte im Kanal durch Änderung des Verhältnisses zwischen DH6T und 6T so zu verändern, dass der Transistor im Verar-mungs- oder Anreicherungsregime betrieben werden kann. Dabei bleibt die Ladungsträ-germobilität auf gleich bleibend hohem Niveau. Dies entspricht dem Dotieren eines anorganischen Halbleiters.
This thesis is centered on studies of phase separation and mixing in co-deposited thin films of rod-like conjugated molecules. The main focus is to determine which molecular properties lead to phase separation and/or mixing of two materials. To address this question I used five materials, of importance in the context of “organic electronics”: pentacene (PEN), quaterthiophene (4T), sexithiophene (6T), p-sexiphenylene (6P), alpha,omega-dihexylsexithiophene (DH6T). With these it was possible to form material pairs which differ in the parameters: energy levels, length of the conjugated core, and alkyl-end-chain-substitution. All films were deposited by organic molecular beam deposition onto the chemically inert substrates silicon oxide and Mylar, a polyethylene terephthalate (PET) foil. The material pairs were deposited simultaneously from two thermal sublima-tion sources. The mixing ratio was controlled by the individual deposition rates, which were measured online by a microbalance. The total deposition rate was 0.5 nm/min, and the film thicknesses ranged from 4 nm to 40 nm. Phase separation is observed for material pairs with dissimilar conjugated core sizes, i.e. [4T/6T]. Noteworthy, the co-deposition of material pairs with similarly sized conju-gated cores [4T/PEN] and [6T/6P] lead to well ordered layered structures. The mole-cules show mixing within layers on a molecular scale and the long molecular axis is ori-ented almost perpendicular to the substrate surface. Material pairs with similarly sized conjugated core and alkyl-end-chain-substitution [6T/DH6T] and [6P/DH6T] show also growth in mixed layered structures. An especially appealing fact is that the interlayer distance increases proportional to the DH6T content in the film. This can be explained with a phase separation into an aromatic and an alkyl domain vertically to the substrate surface. A decrease of the DH6T content in the film leads to a less dense packing in the alkyl domain. This leads, due to the flexibility of the alkyl chains, to a decrease of the overall interlayer distance. The low surface corrugation and the interconnected islands render the material pair [6T/DH6T] well suitable for the use as active layer in organic field effect transistors. It is shown that it is possible to tune the charge carrier density in the channel by changing the ratio between 6T and DH6T. This effect enables switching the transistor from en-hancement to depletion mode, while maintaining a high charge carrier mobility. This is comparable to p-type doping of inorganic semiconductors.

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Fused ring structures such as cyclopentadithiophenes (CPDT), fluorenes and dithienopyrroles have been shown to have low band gaps and extended conjugation lengths. Both of these properties make them interesting materials for organic semiconductor applications. It has been shown that increasing the planarity of building blocks, and in turn the polymer or molecule they are contained within, can improve charge transport by increasing π-π stacking. While the hom*o-polymers of dithienopyrrole, and alkene bridged CPDT and fluorene have low band gaps, it is possible to further reduce them by forming co-polymers, either by combination with an acceptor unit or by increasing the planarity of the polymer. Three families of small molecules and corresponding co-polymers were therefore synthesised using three main building blocks - alkene bridged CPDT, alkylidene fluorene and dithienopyrrole - combined with a series of co-monomers. In the cases of CPDT and dithienopyrrole two different alkyl chains were used with the aim of influencing solubility and solid-state packing. The optical and electrochemical properties were studied and trends determined. In addition physical and thermal properties were studied and for several of the small molecules, crystal structures and theoretical structures were also evaluated to probe intermolecular interactions in the solid state.During the synthesis of one alkylidene fluorene small molecule an unexpected impurity was isolated in which the bridging alkene of the fluorene had rearranged. Possible reasons for the formation were investigated and the properties of the compound studied.Several small molecules and one co-polymer were incorporated into preliminary OFET devices, although performance was limited by poor film formation. Film forming studies were also undertaken on the co-polymer.

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A study of interactions between molecules of the same material was performed on a model polymer system. Regio-regular poly(3-hexylthiophene) (P3HT) self-organises into two-dimensional π-stacked lamellar structures. Although the chains pack at a distance of only 3.8Å, the resonant coulomb interaction between nearest-neighbour molecules is small, owing to large average conjugation lengths within the lamellae. When the resonant coulomb (or excitonic) interaction is smaller than the vibrational relaxation energy, the excitation is localised on a single molecule and the coupling is termed weak. Here we demonstrate that the polymer absorption and emission spectra can be comprehensively explained using a weakly interacting H-aggregate model. Using an analytic form of the model we can estimate the excitonic interaction energy from the ratio of the 0-0 and 0-1 absorbance peaks. It was found to vary between 5-30meV. We use this powerfully simple tool to determine how film micromorphology depends on processing. We find that films spun from low boiling point solvents show a decrease in crystalline quality, an increase in excitonic coupling and more amorphous regions, than films spun from high boiling point solvents. We correlate these findings with field-effect transistor characteristics to produce a model of film micro-morphology. We also demonstrate preliminary results that show that due to the aggregate nature of the primary neutral excitation, photo-induced charge generation in P3HT is due to exciton-exciton annihilation. Finally, we study the intermolecular interactions at an interface between two different molecules (a hole transporting polymer, TFB (Poly(9,9-dioctylfluorene –co-N-(4-butylphenyl)diphenylamine)) and an electron-transporting disoctic, HATNA-SC12 (Hexa-azatrinaphthylene)). Depending on the energetics of the interface between two materials, the inter-molecular state can be stabilised by either coulomb interactions (as in the case of single material interfaces) or charge-transfer interactions. In this case, we find that the charge-transfer interactions dominate and an excited-state complex, or exciplex, is formed. The exciplex is generated efficiently in light-emitting diodes, producing a pure red emission. In polymer/polymer blends efficient bulk exciton emission can occur due to endothermic transfer from the exciplex to the bulk exciton. In this system, however the exciplex is stable at the interface, acting as an energy bottleneck with inefficient transfer to bulk exciton states. Furthermore, the yield of charge separation is low.

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Systeme aus konjugierten Molekülen und Graphenen bergen hohes Potential für Anwendungen. Die Untersuchung ihrer Wechselwirkungsmechanismen ist wichtig für die Entwicklung neuer Anwendungen und Fokus dieser Arbeit: Optische Mikroskopie, Spektroskopie und Rasterkraftmikroskopie werden komplementär verwendet, um die optischen und strukturellen Eigenschaften solcher Systeme zu erforschen. Insbesondere werden (i) die Permeationsbarriere-Eigenschaften von Graphen in-situ auf einem halbleitenden Polymerfilm quantifiziert. Weiterhin werden (ii) die Fluoreszenz- und (iii) Raman-Emission von konjugierten Molekülen in der Nähe von Graphen untersucht und die entsprechenden Kopplungsmechanismen diskutiert. (i) Graphene zeigen sich als effizienter Schutz des empfindlichen Polymers [Poly(3-hexylthiophen)] vor Degeneration durch Sauerstoff und Wasser aus der Umgebungsluft. Dies legt nahe, dass Graphene nicht nur als transparente Elektrode, sondern gleichzeitig als Barriereschicht in künftigen optoelektronischen Bauelementen dienen können. (ii) Es wird gezeigt, dass die bekannten optischen Eigenschaften von Graphen die Existenz stark lokalisierter Graphen-Plasmonen im Sichtbaren implizieren. Durch Verwendung von nanoskaligen Emittern [Rhodamin 6G (R6G)], welche die für effiziente Anregung von Graphen-Plasmonen im optischen Frequenzbereich notwendigen großen Wellenvektor bereitstellen, wird Graphen-Plasmonen-induzierte (GPI) Fluoreszenz-Anregungsverstärkung von nahezu 3 Größenordnungen nachgewiesen. Demnach ist Graphen für plasmonische Bauelemente im Sichtbaren interessant. (iii) Außerdem wird GPI Verstärkung des Raman-Querschnittes von R6G um 1 Größenordnung nachgewiesen. Zukünftige Entwicklung von Antennen für zusätzliche direkte Anregung von Graphen-Plasmonen aus dem Fernfeld macht Graphen vielversprechend für leistungsfähige oberflächenverstärkte Raman-Spektroskopie. Zusammenfassend wurden neue und anwendungsrelevante Einblicke in die analysierten Systeme gewonnen.
Systems of conjugated molecules and graphenes bear high application potential. The investigation of their interaction mechanisms is important for design of new applications and the focus of this thesis: Optical microscopy, spectroscopy and scanning force microscopy are complementarily used to explore the optical and structural properties of such systems. In particular (i) the permeation barrier properties of graphene are quantified in-situ on a semiconducting polymer film. Furthermore (ii) the fluorescence and (iii) Raman emission of conjugated molecules in proximity to graphene are investigated and the respective coupling mechanisms are discussed. (i) Graphenes are found to efficiently protect the sensitive polymer [poly(3-hexylthiophene)] from degradation by oxygen and water from the ambient atmosphere. This suggests that graphenes can not only serve as transparent electrode, but simultaneously as a barrier layer in future optoelectronic devices. (ii) It is shown that the known optical properties of graphene imply the existence of strongly localized graphene plasmons in the visible. Using nanoscale emitters [rhodamine 6G (R6G)] that provide the high wave vectors necessary to efficiently excite graphene plasmons at optical frequencies, graphene plasmon induced (GPI) fluorescence excitation enhancement by nearly 3 orders of magnitude is demonstrated. Graphene is thus interesting for plasmonic devices in the visible. (iii) In addition GPI enhancement of the Raman cross section of R6G by 1 order of magnitude is demonstrated. The future design of antennas for additional direct farfield excitation of graphene plasmons makes graphene promising for powerful surface enhanced Raman spectroscopy. In summary new and application relevant insights were gained into the studied systems.

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With many interesting electronic and optical properties, conjugated molecules have long been a subject for both theoretical and experimental studies, especially in recent applications in optoelectronics. Most of the properties are controlled by their electronic structures, with the low-lying states predominantly characterised by the 7!'-electrons. We have thus employed the semi-empirical Pariser-Parr-Pople model, whose Hamiltonian parameters are optimised against the excited states, in this study. Despite only considering the π-delocalised system, the model has been widely and successfully applied to study such molecules, giving fairly accurate results. The calculation of these strongly correlated systems requires an accurate computational method, which is usually limited to small molecules due to an enormous amount of resources demanded, as in ab initio calculations. Density Matrix Renormalisation Group (DMRG) provides a systematic way to truncate the size of the Hilbert space while being able to reasonably capture the correlation effect. We have compared three different approaches using both localised and delocalised basis states in the DMRG calculations. First, in the real-space method, atomic sites are aligned on the one-dimensional DMRG lattice as originally developed to study the fermionic systems in condensed matter physics. Alternatively, a collection of atoms, e.g. a monomer unit in conjugated polymers, can be used where an in situ optimisation technique is employed to pre-select the important states. Last, the correlation effect between the Hartree-Fock (HF) molecular orbitals on the lattice sites is calculated in the HF -DMRG scheme. In this post-HF method, the energy converges more slowly than the first but the implementation of t he codes is generic to any geometric structures. In addition to the spin-flip and particle-hole symmetries, which are available in the real-space method, the spatial symmetries can also be applied to target specific states when working in HF space. Calculations have been made on conjugated polymers, i.e. polyacetylene and poly(parophenylene), and aromatic compounds, i.e. pentacene and porphin. The results are compared to other methods, e.g. exact diagonalisation and Configurational Interaction Singles, as well as other theoretical and experimental results in the literature

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This thesis focuses on two different, but equally challenging, areas of computational chemistry: transition metal organic molecule interactions and parameterisation of organic conjugated polymers for molecular dynamics simulations. The metal-binding properties are important for understanding of biomolecular action of type 2 diabetes drug and development of novel protocols for redox calculations of copper systems. In this area the challenge is mainly related to the complex electronic structure of the open-shell transition metals. The main challenges for the parameterisation of conjugated polymers are due to the size of the studied systems, their conjugated nature and inclusion of environment. Metal-binding properties as well as electronic structures of copper complexes of type 2 diabetes drug metformin (Metf) and other similar, but often inactive, compounds were examined using DFT method. It was found that for neutral compounds it is not possible to explain the differences in their biological effects solely by examining the copper-binding properties. Further, the proposed mechanism potentially explaining the difference in the biomolecular mode of action involves a possible deprotonation of biguanide and Metf compounds under higher mitochondrial pH which would lead to formation of more stable copper complexes and potentially affecting the mitochondrial copper homeostasis. In addition, redox properties of copper-biguanide complexes could interfere with the sensitive redox chemistry or interact with important metalloproteins in the mitochondria. Understanding the copper-binding properties is also important for a systematic development and testing of computational protocols for calculations of reduction potentials of copper complexes. Copper macrocyclic complexes previously used as model systems for redox-active metalloenzymes and for which experimentally determined redox potentials are available were used as model systems. First adequacy of using single reference methods such as DFT was examined for these systems and then various DFT functionals and basis sets were tested in order to develop accurate redox potential protocol. It was shown that good relative cor-relations were obtained for several functionals while the best absolute agreement was obtained with either the M06/cc-pVTZ functional with the SMD or either M06L or TPSSTPSS functional with cc-pVTZ basis set and the PCM solvation model. Organic conjugated polymers have a great potential due to their application in organic optoelectronics. Various wavefunction and DFT methods are utilized in order to systematically develop parameterisation scheme that can be used to derive selected force-field parameters such as torsional potentials between monomer units that are critical for these systems and partial charges. Moreover, critical points of such a parameterisation are addressed in order to obtain accurate MD simulations that could provide valuable insight into material morphology and conformation that affect their optical properties and conductivity. It was shown that a two step approach of geometry optimisation with CAM-B3LYP/631G* and single point (SP) energy scan with CAM-B3LYP/cc-pVTZ is able to yield accurate dihedral potentials in agreement with the potentials calculated using higher level methods such as MP2 and CBS limit CCSD(T). Further, investigating partial charge distribution for increasing backbone length of fluorene and thiophene it has been found that it is possible to obtain a three residue model of converged charge distributions using the RESP scheme. The three partial charge residues can be then used to build and simulate much longer polymers without the need to re-parametrize charge distributions. In the case of side-chains, it was found that it is not possible to obtain converged charge sets for sidechain lengths of up to 10 carbons due to the strong asymmetry between the side-chain ends. Initial validation of derived force-field parameters performed by simulations of 32mers of fluorene with octyl side-chains (PF8) and thiophene with hexyl side-chains (P3HT) in chloroform and calculation of persistence lengths and end-to-end lengths showed close correspondence to experimentally obtained values.

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This thesis reports structure-property relationships in a range of conjugated molecules where the nature of the delayed fluorescence (DF) is used as a powerful diagnostic tool in order to gain insight into the nature of the molecules. All the investigations revolve around using three spectroscopic methods; steady state, single-photon counting and particularly time-resolved nanosecond spectroscopy. The rarely observed optically generated geminate electron-hole (e-h) pair recombination is designated as the origin of DF in Rhodamine 6G and its derivative ATTO-532 molecules. The DF shows a strong dependence on excitation energy, which is due to emission arising from higher energy excited dimeric states. In addition, the complex excited-state nature of the polyspirobifluorene (PSBF) polymer is investigated in both dilute solutions and spin-coated films. According to investigations carried out in dilute solutions, solvent polarity and temperature dependent charge transfer (CT) state formation is observed as arising from the “inter/intrachain” interaction phenomena. The stabilisation of the intra- CT state at low temperatures exhibits the presence of both triplet-triplet annihilation (TTA) and monomolecular processes. These findings are used to interpret the up-conversion data of PSBF in thin films, clearly revealing that both TTA and thermally activated delayed fluorescence (TADF) are involved in indirect singlet generation. The same mixed contribution is also confirmed in anthracene based, small molecule, thin films. Consequentially, these findings highlight the investigated system as one of the desirable alternative molecular systems through which high efficiencies in organic light emitting device (OLED) applications can be attained. Finally, an understanding of novel anthracene based novel acceptor molecule is developed through the use of a sensitizer based up-conversion experimental method, in which the question of how the side groups (having different electron affinities) affect the TTA efficiency and triplet energy transfer efficiency is clarified. Lastly, the investigations show that novel pyridine derivatives have solvent polarity and viscosity dependent excited state configurations, which are designated as twisted/wagged intramolecular charge transfer states. The DF, in this case, predominantly originates from monomolecular recombination of the geminately bound e-h pairs. It is believed that this can be a major loss mechanism for quantum yield in ICT systems.

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The main focus of this thesis is on the aromaticity of the ground state and electronically excited states of π-conjugated molecules and polymers, as well as how aromaticity is connected to their properties. The electronic structures of polybenzenoid hydrocarbons (PBHs) were explored through density functional theory (DFT) calculations and the π-component of the electron localization function (ELFπ). The study revealed how the π-electronic structure is influenced by the fusion of double bonds or benzene rings to the PBHs. We also demonstrated that the π-electrons of benzene extend to accommodate as much aromaticity as possible when bond length distorted. The aromatic chameleon property displayed by fulvenes, isobenzofulvenes, fulvalenes, bis(fulvene)s, and polyfulvenes were investigated using DFT calculations. The tria-, penta-, and heptafulvenes were shown to possess ionization energies and electron affinities which can be tuned extensively by substitution, some of which even outperform TTF and TCNQ, the prototypical electron donor and acceptor, respectively. The singlet-triplet energy gap of pentafulvenes can be tuned extensively by substitution to the point that the triplet state is lower than the singlet state and thus becomes the ground state. The ELFπ of isobenzofulvene shows that the benzene ring in an electronically excited state can be more aromatic than the corresponding ring in the ground state. We have shown that the 6-ring of [5.6.7]quinarene is influenced by a Hückel aromatic resonance structure with 4n+2 π-electrons in the excited quintet state. The bis(fulvene)s which are composed of a donor type heptafulvene and an acceptor type pentafulvene, retain the basic donor-acceptor properties of the two fragments and could function as compact donor-acceptor dyads. A few of the designed polyfulvenes were found to have band gaps below 1 eV at the PBC-B3LYP/6-31G(d) level. Various 2,7-disubstituted fluorenones and dibenzofulvenes were synthesized and their excited state properties were investigated by absorption spectroscopy and time-dependent DFT calculations. It was found that the 1A → 1B transition of ππ* character can be tuned by substitution in the 2,7-positions. The 2,7-bis(N,N-dimethyl) derivatives of fluorenone and dibenzofulvene displayed low energy transitions at 2.18 and 1.61 eV, respectively, in toluene.

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Organic semiconductors (OSCs), compared to the more traditional silicon, are enticing materials for the fabrication of optoelectronic devices (e.g., transistors, photovoltaic cells, light-emitting diodes) due notably to the lower cost associated with their preparation and purification, as well as their increased solubility in solvents which can accommodate large-scale fabrication. However, a higher degree of molecular disorder typically results in lower performance than silicon and remains an issue to be adressed. As the structure of an OSC is crucial to its performance, understanding the nature of this structure-property relationship is key to further the field of OSCs. In this regard, this thesis explores the optoelectronic properties of different π-conjugated organic frameworks which incorporate sulphur and nitrogen atoms along the rigid conjugated backbone for their desirable impacts on charge mobilities and stability. After a brief review of both small-molecule OSCs as well as key experimental techniques employed in the course of this work, chapter three covers the synthesis and characterization of dithiatetrazocines (DTTA), electron-deficient sulphur-nitrogen heterocycles, which were functionalized with various (oligo)thienyls pendants. The impact of both the substitution patterns and the degree of conjugation on the optoelectronic and solid-state properties of the ring system was investigated.The fourth chapter expands on previous work from the Brusso group that focused on extending the 2D conjugation of tetrathienoanthracene. While oligothienyls were previously shown to effectively increase the degree of conjugation, little to no change in device performance were observed, which was ascribed to disorder of the rotatable pendants. Here, rigid thieno[3,2-b]thiophene was used instead to increase both the degree of conjugation while maintaining structural rigidity, as assessed by optical, electrochemical and theoretical studies.The fifth chapter introduces preliminary work toward expanding the electron-deficient hexaazatrinaphtylene core with thiophene rings. The resulting concentric donor-acceptor structure promotes luminescent behavior with pronounced emission solvatochromism. Optical measurements were performed before and after intramolecular cyclization of the thiophene rings, to study the impact of aromatization on the optoelectronic properties of the system.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
PROGRAMA DE EXCELENCIA ACADEMICA
Este trabalho teve como objetivo fabricar e caracterizar Transistores Orgânicos Emissores de Luz (OLETs, Organic light-Emitting Transistors). Os OLETs combinam em um único dispositivo a funcionalidade elétrica de um transistor de efeito de campo orgânico e a capacidade de geração de luz, representando uma nova classe de dispositivos orgânicos com alto potencial de inovação em aplicações, como sistemas ópticos de comunicação, tecnologia de displays avançada, lasers orgânicos, fontes de luz em nanoescala e optoeletrônica orgânica integrada. Portanto, esta tese possui um caráter pioneiro, tanto para grupo de pesquisa quanto para o país, uma vez que ocorre a junção dos conhecimentos e domínio adquiridos sobre OFETs e OLEDs. Efetivamente, este trabalho de doutorado consistiu na fabricação e caracterização sistemática de diversos dispositivos OLET utilizando variadas arquiteturas e diversos materiais, comerciais e não comerciais, como o NT4N, o P13 e uma bicamada de C8-BTBT com TcTa:Ir(ppy)3. Os dispositivos foram caracterizados através de medidas elétricas e óticas, obtendo-se as curvas características. Também foram determinados seus parâmetros e propriedades de funcionamento, com destaque para as mobilidades de carga e para as eficiências obtidas. Houve também o entendimento e a implementação de um tratamento térmico na camada dielétrica, sendo parte fundamental da fabricação dos dispositivos. Os dispositivos fabricados apresentaram diferentes graus de desempenho, com destaque para a arquitetura bicamada, por apresentar a maior potência luminosa (4 microwatt) e a maior eficiência (0,5 por cento), sendo suficientes para inserir os dispositivos fabricados na categoria de dispositivos orgânicos altamente eficientes. Tal fato demonstra que o domínio da fabricação e da caracterização desta nova classe de dispositivos foi alcançado.
The aim of this work was to achieve the knowledge of the fabrication and the characterization of Organic Light Emitting Transistors, OLETs, considered as one of the innovative technologies nowadays. The OLETs combine in a single device the electrical functionality of an organic field-effect transistor (OFET) and the light-generating capability. They represent a promising new class of organic devices with high potential for innovation in applications such as communication systems, advanced display technology, organic lasers, nanoscale light sources and integrated organic optoelectronics. In some way, this thesis has a pioneercharacter, both for our research group and for the country, since it combines different knowledge and skills about OFETs and OLEDs to achieve a new device. Actually, this work involved the systematic manufacture and characterization of several OLETs using different architectures employing commercial and noncommercial materials, such NT4N, P13 and a bilayer of C8-BTBT with TcTa:Ir(ppy)3. The devices were then characterized by electrical and optical measurements. The working parameters and properties were determined as well, highlighting the charge carrier mobilities and efficiencies obtained. The understanding and the implementation of a specific heat treatment in the dielectric layer was a fundamental part of this work for the manufacture of the devices which have different degrees of performance. With emphasis on the bilayer architecture, that presented the highest luminous power (4 microwatt) and efficiency (0,5 percent), inserting the devices manufactured in the category of highly efficient organic devices. Such fact shows that the fabrication and characterization of this new class of devices has been achieved.

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学位授与大学：京都大学 ; 取得学位: 博士(工学) ; 学位授与年月日: 2007-09-25 ; 学位の種類: 新制・課程博士 ; 学位記番号: 工博第2867号 ; 請求記号: 新制/工/1421 ; 整理番号: 25552
Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第13396号
工博第2867号
新制||工||1421(附属図書館)
25552
UT51-2007-Q797
京都大学大学院工学研究科分子工学専攻
(主査)教授 今堀 博, 教授 川﨑 昌博, 教授 榊 茂好
学位規則第4条第1項該当

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Ce travail porte sur la synthèse et l’évaluation de systèmes pi-conjugués en tant matériaux actifs pour des dispositifs opto(électroniques). Un premier chapitre décrit une série d’oligothiophènes cruciformes et leur évaluation dans des dispositifs électrochromes. Le second chapitre décrit la synthèse d’accepteurs moléculaires à base de benzodithiophène et l’analyse de leur potentialités comme matériaux accepteurs dans des cellules solaires organiques. La plus large part du travail porte sur l’analyse des relations structure-propriétés d’une série de petites molécules push-pull comportant un groupe donneur triphénylamine (TPA) relié à un groupe accepteur par un espaceur thiényl. Une première étape a consisté à remplacer l’un des cycles phényles de la TPA par des groupes aromatiques tels que p-fluorophényle, anthryle et naphtyle. Ces modifications ont peu d’influence sur les propriétés électroniques de la molécule mais induisent de large variations des propriétés de transport de charge et de conversion photovoltaïque des matériaux correspondants. Au cours d’une seconde étape l’un des groupes phényles de la TPA a été remplacé par des chaînes alkyle, perfluoroalkyle et oligo(oxyethylene). Les résultats de diffraction X, spectroscopie d’absorption et de fluorescence, génération de second harmonique et électrochimie démontrent que certaines de ces molécules présentent des propriétés d’émission contrôlées par agrégation tandis que les matériaux correspondants se réorganisent spontanément à l’état solide sous forme d’agrégats H ou J dotés de propriétés de transport de charges et de conversion photovoltaïque fortement améliorées et de propriétés d’absorption, d’émission et de génération de second harmonique mécaniquement modulables
This work deals with the design, synthesis and evaluation of molecular pi-conjugated systems as active materials for (opto)electronics devices. A short first chapter describes three X-shaped oligothiophenes, thecharacterization of their structure and properties and a first evaluation of their performances in electrochromic devices. The second chapter describes the synthesis of molecular acceptors based on a benzodithiophene and the analysis of their potentialities when combined with molecular donors in organic solar cells.The major part of the work is focused on the analysis of structure-properties relationships of a series of smallpush-pull molecules involving di- or tri-arylamine donorblocks linked to an acceptor group by a thienyl bridge. In a first step, a phenyl ring of triphenylamine (TPA) is replaced by p-fluorophenyl, anthryl and naphtyl groups.Optical and electrochemical results show that substitution has little effect at the molecular level but can markedly affect solid-state properties with in particular an improvement of charge-transport and short-circuit current density of solar cells based on these donor materials.In a second step, a phenyl ring of TPA is replaced by alkyl, perfluoroalkyl and oligo(oxyethylene) chains. Results of X-ray diffraction, absorption and photoluminescence spectroscopies, second harmonic generation, and electrochemistry demonstrate that some of these molecules under go aggregation controlled photoluminescence emission wave length while the corresponding materials spontaneous lyre organize in the solid-state to form either H or Jaggregates with enhanced charge mobility, photovoltaic conversion efficiency and mechanically-induced chromism, fluorochromism and NLO-chromism

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Molecular layers of polymethine dye long conjugation chain on glass contain several types of molecularnanocomponents. The number and type of the components depend on the thickness of a layer. In thin layers,only monomolecular components (all-trans-stereoisomers and cis-isomers) are present. We studied aseries of four dicarbocyanines and determined the steric structure of the nanocomponents of the layers.The layers of less than 1 monolayer thick contain up to 4 monomeric components. For monocis- and dicisisomersof the dyes studied, which are obtained from the all-trans form upon rotation of fragments of amolecule around different bonds in the conjugated chain, the steric models were constructed. It was shownthat in the series of polymethine molecules differing in the substituents and their positions in the chainthere is a correlation between the intensity of the absorption bands of the certain components and the sterichindrance of molecular isomers. The above correlation may be used for the determination of the stericstructure of monomeric components of the layer.When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34890

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Diese Arbeit behandelt elektronische und strukturelle Eigenschaften dünner Schichten aus konjugierten organischen Molekülen (COMs), aufgebracht auf Metalloberflächen per Vakuum-Sublimation. Diese Eigenschaften sind essenziell für Funktionsrealisierung und -optimierung organischer Elektronikbauteile. Teil 1 diskutiert zwei Ansätze zur Energieniveauanpassung (ELA) an Organik-Metall-Grenzflächen zur Einstellung der dortigen Löcherinjektionsbarrieren (HIBs) durch (Über-)Kompensation des abträglichen "Push-back"-Effekts: - Ausnutzung der besonderen ELA bei Chalkogen-Metall-Bindungen, hier gezeigt mit Hilfe von Röntgen- und Ultraviolettphotoelektronenspektroskopie (UPS/XPS) für ein Seleno-funktionalisiertes COM - Einfügen von COMs mit ausgeprägtem Elektronen-Akzeptorcharakter vor dem Aufbringen der aktiven Schicht. UPS-Messungen zeigen, dass beide Ansätze HIBs von ca. 0.3 eV ermöglichen. Teil 2 untersucht ausgewählte organische Heterostrukturen auf Metallen. Die Untersuchungen identifizieren einen Ladungstransfer vom Metall zur Überschicht (MOCT) als verantwortlich dafür, das System bei Ferminiveau-Pinning in den Gleichgewichtszustand zu überführen. Detaillierte Untersuchungen gestatten die Identifikaton von ganzzahligem Ladungstransfer zu einem Teil der Moleküle in der ersten Überschichtlage und den Einfluss der Dipol-Abstoßung in der Überschicht. In Teil 3 dienen Metalloberflächen als Auflage für supramolekulare Architekturen mit dipolaren Bausteinen. Rastertunnelmikroskopie (STM) an einer Serie von teils partiell fluorierten, stäbchenförmigen COMs mit unterschiedlich großen Dipolmomenten ermöglicht die Entflechtung von Dipol-Dipol- und konkurierenden Wechselwirkungen physisorbierter Submonolagen auf Ag(111). Ein anderes, stark dipolares COM bildet bei Monolagenbedeckung auf Au(111) sechs Phasen, alle mit antiferroelektrischer Einheitszellen. UPS-Messungen ergeben eine bevorzugte Ausrichtung der Moleküle in Multilagen.
In this thesis, the electronic and structural properties of thin films of conjugated organic molecules (COMs) vacuum-deposited on metal surfaces are studied. These properties are essential for realization and optimization of device functionalities in the field of organic electronics. Part 1 discusses two approaches for engineering the energy-level alignment (ELA), and, thereby, optimizing hole injection barriers (HIBs), at organic/metal interfaces via (over)compensation of the detrimental "push-back": - Exploiting the peculiar ELA at chalcogen-metal bonds, shown here (with X-ray and ultraviolet photoelectron spectroscopy, UPS/XPS) for a seleno-functionalized COM - inserting electron-accepting COMs prior to deposition of active layers. UPS shows that both approaches realize HIBs into the active COM as low as 0.3 eV. Part 2 studies selected organic/organic heterostructures on metal surfaces. These studies allow to propose that metal to overlayer charge transfer (MOCT), is responsible for achieving electronic equilibrium when such systems are Fermi-level pinned. Detailed investigations allowed identifying integer charge transfer to a fraction of the molecules in the first overlayer and the influence of the dipole-repulsion on the overlayer. In Part 3, metal surfaces are used as support for supramolecular architecture with polar building blocks. Scanning tunneling microscopy (STM) of a series of rod-like COMs with and without partial fluorination and with different dipole moments help disentangling the delicate balance dipole-dipole and competing interactions for sub-monolayer films physisorbed on Ag(111). For another, highly-polar COM at ca. monolayer coverage on Au(111), STM identifies six phases. All phases are found to exhibit anti-ferroelectric unit cells. UPS evidences a preferential alignment of multilayer molecules.

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This dissertation is devoted to the study of third-harmonic generation (THG) in push-pull chromophore-doped polymer films. This kind of films, with amorphous structure, exhibit null second harmonic generation but strong THG when pumped at the fundamental wavelengths within the telecommunication range (1.4-1.6 μm). It is demonstrated that at 1550 nm, micrometer-thick samples generate up to 17 muW of green light with an input power of 250 mW delivered by an optical parametric oscillator. This high conversion efficiency is achieved without the use of phase matching or cascading of quadratic nonlinear effects and it is due to high values of the third-order nonlinear susceptibility combined with weak film absorption at the third harmonic wavelength. The efficient THG process opens the doors to low cost and sensitive third-order optical autocorrelation and cross-correlation applications. So, in addition to the basic research performed about the characterization of the THG in push-pull chromophore-doped polymer films, two applications are demonstrated. The first is the complete diagnostic of femtosecond pulses by THG-Interferometric Autocorrelation and by THG Frequency-Resolved Optical Gating. The second is the THG-Cross-correlation Time-Gated Imaging of objects embedded in highly scattering conditions.

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The principal aim of this thesis is the understanding of the electronic structure of organic diradical and polyradical molecules. Unveiling the properties that give them the electronic, magnetic, and optical properties to be applied as main components in optoelectronic devices. Specifically, the objectives that have been achieved are i) the characterization of organic compounds with diradical and polyradical character, and their electronic, magnetic, and spectroscopic properties; ii) the detailed description of the singlet fission mechanism, as well as the proposal of a new system that, theoretically, is able of carrying out efficiently the singlet fission process; and iii) the use of quantum mechanical methods (specifically RAS-SF) and computational tools to get a proper description of the electronic structure of the ground state of systems in which non-dynamic correlation plays an important role.In the first place, organic compounds whose optical and magnetic properties make them interesting in the field of optoelectronic materials were studied. The relationship between molecular structure and the radical character was found by the study of linear and cyclic acenes and small triangular fragments derivatives of graphene. While the diradical and tetraradical character increase together with the size of the linear and cyclic compounds, the triangular structures (TGNF, the acronym for Triangulene Graphene Nano Fragments) are open-shell systems with high-spin ground state multiplicity. Furthermore, a manner to tune the spin multiplicity in the ground state of TGNFs is proposed through heteroatom doping or hydrogenation, which offers a way to design larger graphene nanofragments with well-defined spin-multiplicity. Towards larger systems, the increment of the size is associated with the increase of the polyradical character. This thesis presents the rationalization of the electronic structure of organic macrocycles with high polyradical character. Concretely, from triradicals to decaradicaloids (up to 10 radical centers). The properties triggered by the open-shell character of the ground state are as diverse as surprising. For instance, AWA systems (annulenes-within-annulenes) have been characterized in collaboration with experimental groups for the first time. The global aromaticity exhibit by these macrocycles responds to the radical interaction in each of the annulenes and is governed by both aromaticity rules, Hückel's, and Baird's simultaneously.On the other hand, the singlet fission process (SF) was expanded from the classical model, which involves five electronic states, to a model that includes double excitations (D states), a seven-state model. Using a simple model, it is estimated that the D states can play an active role in SF, as well as the necessary conditions to maximize their participation as an initial or intermediate state in the process. The feasibility of spiro systems carrying out SF is exposed.
El principal objetivo de esta tesis es poner al descubierto las propiedades químicas que permiten que procesos fotofísicos complejos tomen lugar en moléculas orgánicas, y que les permite tener aplicaciones en materiales optoelectrónicos.Puntualmente, los objetivos que se han cumplido son i) la caracterización de di y poliradicales orgánicos y sus propiedades electrónicas, magnéticas y espectroscópicas; ii) la descripción detallada del mecanismo de fisión de singuletes, así como proponer un sistema que teóricamente es capaz de realizarlo eficientemente; y iii) la utilización de métodos de la mecánica cuántica (específicamente RAS-SF) y herramientas computacionales que permiten la descripción apropiada de la estructura electrónica del estado fundamental de sistemas en los que la correlación no-dinámica representa un papel importante. En primer lugar, se estudiaron compuestos orgánicos cuyas propiedades ópticas y magnéticas los hacen interesantes en el campo de materiales optoelectrónicos. Se encontró la dependencia del carácter radical en la topología de nanoestructuras de grafeno (acenos) lineales y cíclicos, y pequeñas laminas de estructura triangular. Mientras el carácter diradical y tetraradical crece con el tamaño de los compuestos lineales y cíclicos, las estructuras triangulares (TGNF, siglas en inglés de Triangulene Graphene Nano Fragments) son compuestos de capa abierta. Además, se propone una forma de modular la multiplicidad de espín en el estado basal de los TGNF mediante el dopaje con heteroátomos. El incremento del tamaño del sistema permite obtener molecular con alto carácter poliradical. En esta tesis se presenta la racionalización de la estructura electrónica de macrociclos orgánicos con carácter triradical hasta decaradicaloide (10 centros radicalarios). Las propiedades que se derivan de estas características son tan variadas como sorprendentes, por ejemplo, se han caracterizado sistemas AWA (anulenos-dentro de-anulenos) cuya aromaticidad global responde a la suma de la aromaticidad en cada uno de los anulenos y esta regida por las reglas de aromaticidad de Hückel y Baird simultaneamente.El proceso de fisión de singuletes (SF) fue expandido del modelo clásico, que involucra cinco estados electrónicos, a un modelo que incluye excitaciones dobles (estados D), modelo de siete estados. Usando un modelo sencillo se estima que los estados D pueden jugar un papel activo en SF, así como las condiciones necesarias para maximizar su participación como estado inicial o intermediario en el proceso. Se expone la factibilidad de que los sistemas spiro lleven a cabo SF.

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The utility of conjugated small molecules and polymers as organic semiconductors have seen a tremendous growth in research and development in academia as well as industry because of their processability and flexibility advantages in comparison to inorganic semiconductors. The extensive research over the years has produced a large number of p-type (hole conducting) and n-type (electron conducting) semiconductors that can be used to construct organic electronic devices. Of these materials, p-type semiconductors are more established and extensively studied because of the ease of preparation as well as their better general stability in comparison to n-type materials. Despite recent research into the development of n-type materials, fullerene (C60 and C70) and its derivatives are still the predominant materials used as electron acceptors for OPV applications. By taking advantage of the electron accepting behavior of cyclopenta[hi]aceanthrylene fragment of C70, we have designed and synthesized new materials based on cyclopenta-fused polycyclic aromatic hydrocarbons (CP-PAHs). By using a newly developed palladium catalyzed cyclopentannulation methodology, 1,2,6,7- tetraarylcyclopenta[hi]aceanthrylenes were prepared by treating diarylethynylenes with 9,10-dibromoanthracene. Scholl cyclodehydrogenation was used to close the externally fused aryl groups to provide access to contorted 2,7,13,18- tetraalkoxytetrabenzo[f,h,r,t]rubicenes. The contortion provides access to more soluble materials than their planar counterparts but still ii allows significant pi-pi stacking between molecules. Using a modified palladium catalyzed cyclopentannulation polymerization followed by a cyclodehydrogenation reaction, a nonconventional synthesis of CP-PAH embedded ladder polymers was also achieved. These ladder polymers possess broad UV-Vis absorptions and narrow optical gaps of 1.17-1.29 eV. The synthesis of new donor-acceptor copolymers incorporating electron accepting 1,2,6,7- tetra(4-dodecylphenyl)dicyclopenta[cd,jk]pyrene was also achieved. The donor unit was varied between thiophene, bithiophene, and 1,4-diethynyl-2,5-bis((2-octyldodecyl)oxy)-benzene producing polymers with high molecular weights and considerably low band gaps. This newly developed cyclopentannulation method was also used to synthesize a new class of stabilized pentacene derivatives with externally fused five-membered rings. The target compounds were synthesized via chemical manipulation of a partially saturated 6,13-dibromopentacene precursor that can be fully aromatized in a final step via a DDQ mediated dehydrogenation reaction. Photodegradation studies reveal the new 1,2,8,9-tetraphenyldicyclopenta[fg,qr]pentacene derivatives are more photostable than TIPS-pentacene, and possess narrow optical gaps of ~1.2 eV. Because anthradithophene (ADT) is more stable than pentacene while maintaining good electronic properties, the synthesis of cyclopentannulated anthradithiophenes (CP-ADTs) was also explored. Synthesis of a highly contorted ADT analogue was achieved by treating 5,11-dibromo-anthradithiophene with 3,3’-dimethoxy,1,1’-diphenyl acetylene under palladium catalyzed cyclopentannulation conditions followed by Scholl cyclodehydrogenation.

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Negli ultimi anni, i materiali funzionalizzati ibridi hanno iniziato ad essere largamente impiegati in applicazioni altamente tecnologiche, dai sensori bio/medicali alla produzione di energie rinnovabili. Per questa ragione sono diventati l’oggetto di diversi studi nell’ambito della scienza dei materiali. Allostesso tempo, le molecole organiche coniugate sono state intensivamente analizzate per via delle loro proprietà particolari riconducibili alla presenza di un lungo sistema di legami π, dalla possibilità di condurre elettricità al loro largo spettro di assorbimento della radiazione luminosa. Questo lavoro ditesi si è concentrato sull’introduzione di questi sistemi all’interno di due tipi di materiali ibridi, dei dispositivi fotovoltaici per la produzione di elettricità (in particolare delle celle solari sensibilizzate a coloranti) e di carburanti alternativi (idrogeno), e degli idrogel biocompatibili sensibili agli stimoli (capacidi condurre elettricità e di reagire a stimoli luminosi), ed inoltre sullo studio della loro influenza sulle caratteristiche del materiale finale.
In recent years hybrid functional materials began to be employed in a series of technologically advanced applications spanning from bio/medical sensors, to renewable energy generation. For this reason, they became the focus of several studies in the field of materials science. At the same time, conjugated molecules have also been intensively investigated, due to the properties arising by the presence of long π-conjugated systems, from the possibility to conduct electricity to the ability to absorb light in a wide range of wavelengths. This PhD work focused on the introduction of such systems in two different kinds of hybrid materials, namely photovoltaic devices for the production of electricity (in particular Dye Sensitzed Solar Cells) and alternative fuels hydrogen), and biocompatible stimuli-responsive hydrogels (capable to conduct electricity and to react upon irradiation), and on the study of their influence on the characteristics of the final material.
Ces dernières années, les matériaux fonctionnels hybrides ont commencé à être employés pour des applications de la haute technologie, allant des senseurs bio/médicaux, à la production d’énergie renouvelable. Pour cette raison, ils sont devenus le centre de plusieurs études dans le domaine dessciences des matériaux. Simultanément, des molécules conjuguées ont été examinée intensément à cause de leurs propriétés venant de leurs longs systèmes π, allant de la possibilité de conduire l’électricité, à leur capacité d’absorber la lumière dans une grande fenêtre spectrale. Le travail de cettethèse se concentre sur l’introduction de tels systèmes dans deux sortes de matériaux hybrides, les dispositifs photovoltaïques pour la production d’électricité (en particuliers les cellules solaires à pigment photosensible) et de carburants alternatifs (hydrogène), et pour les hydrogels biocompatiblessensibles aux stimuli (capables de conduire l’électricité et de réagir sous irradiation), et sur l’étude de leur influence sur les caractéristiques du matériau final.

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Ces dernières années, les matériaux fonctionnels hybrides ont commencé à être employés pour des applications de la haute technologie, allant des senseurs bio/médicaux, à la production d’énergie renouvelable. Pour cette raison, ils sont devenus le centre de plusieurs études dans le domaine des sciences des matériaux. Simultanément, des molécules conjuguées ont été examinée intensément à cause de leurs propriétés venant de leurs longs systèmes π, allant de la possibilité de conduire l’électricité, à leur capacité d’absorber la lumière dans une grande fenêtre spectrale. Le travail de cette thèse se concentre sur l’introduction de tels systèmes dans deux sortes de matériaux hybrides, les dispositifs photovoltaïques pour la production d’électricité (en particuliers les cellules solaires à pigment photosensible) et de carburants alternatifs (hydrogène), et pour les hydrogels biocompatibles sensibles aux stimuli (capables de conduire l’électricité et de réagir sous irradiation), et sur l’étude de leur influence sur les caractéristiques du matériau final
In recent years hybrid functional materials began to be employed in a series of technologically advanced applications spanning from bio/medical sensors, to renewable energy generation. For this reason, they became the focus of several studies in the field of materials science. At the same time, conjugated molecules have also been intensively investigated, due to the properties arising by the presence of long π-conjugated systems, from the possibility to conduct electricity to the ability to absorb light in a wide range of wavelengths. This PhD work focused on the introduction of such systems in two different kinds of hybrid materials, namely photovoltaic devices for the production of electricity (in particular Dye Sensitzed Solar Cells) and alternative fuels (hydrogen), and biocompatible stimuli-responsive hydrogels (capable to conduct electricity and to react upon irradiation), and on the study of their influence on the characteristics of the final material

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This thesis is concerned with the photophysical and nonlinear optical responses, and applications of a set of conjugated polymers and small molecules in the visible and near-IR spectral regions. Poly(phenylene ethynylene) PPE polymers were substituted with conjugated side-arms in a cruciform fashion to determine the impacts of electronic coupling on the one-photon (1PA), two-photon (2PA), and excited state absorption (ESA) properties of the co-polymer system. The cruciform-like PPEs showed significant changes in their nonlinear and phophysical behavior relative to their linear models, including shifts and splittings of the 1PA bands due to moderate mixing of the lowest singlet excited states, an increase in the 2PA cross section (δ) values, and an increase in the yield of triplet excited-state species. The cruciform-like PPE polymers exhibited effective optical pulse suppression of femtosecond and nanosecond laser pulses over a broad spectral range of ~200 nm in the visible and near-IR. The suppression capability of the cruciform-like PPEs exceeded the best reported value for alkyl-substituted PPE polymers. The spectroscopic effects due to conjugation length, structural configuration, and intramolecular charge transfer (ICT) are discussed for a family of bent donor-acceptor-donor (D-A-D) -type conjugated oligomers, which incorporate electron-rich triarylamine donors and electron-deficient triarylborane acceptor units into its conjugated structure. These organoborane oligomers are highly fluorescent and exhibit strong 2PA in the visible region with δ values as large as 1410 GM, as well as overlapping ESA bands attributed to singlet-singlet and triplet-triplet absorption. Saturation of the molar absorptivity, ε, and δ was observed at less than two repeat monomer units due to conformational disorder in the oligomer with increasing length. Positive solvatochromism of fluorescence with solvent shifts as large as ~70 nm was observed as a result of ICT from the arylamine donors to boryl-centered acceptor sites. The excited-state dynamics also show sensitivity to the solvent environment. Experimental findings suggest that these organoborane oligomers may have potential use as nonlinear material for optical power limiting (OPL) and two-photon sensing applications. The spectral properties of two bis-donor chromophores, (bis(diarylamino)biphenyl (TPD) and distyrylthiophene (DST), were investigated with and without the presence of AgNPs in order to better understand the local-field enhancement and subsequent effects on the photophysics and nonlinear behavior of 2PA dyes. While little changes were observed in the excited-state dynamics, measurements of nanoparticle aggregate-dye composite solutions with TPD revealed a 1.6-enhancement in the two-photon excited fluorescence signal. OPL measurements of nanosecond laser pulses at 532 nm revealed a reduction in threshold energy by a factor of 2 in solutions containing TPD and AgNP aggregates, relative to solutions of TPD alone. DST shows exceptional solubility (>1 M) in several organic solvents and exhibits a 2PA spectrum that overlaps well with its singlet-singlet and triplet-triplet ESA bands. Consequently, DST exhibits effective optical limiting of nanosecond laser pulses through two-photon induced excited-state absorption over a broad spectral range of approximately 200 nm in the red and near-IR.

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APA, Harvard, Vancouver, ISO, and other styles

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Abstract:

Organic photovoltaics have attracted considerable research and commercial interest due to their lightness, mechanical flexibility and low production costs. There are two main approaches for the fabrication of organic solar cells – solution and vacuum processing. The former relies on morphology control in polymer-fullerene blends resulting from natural phase separation in these systems. The latter takes advantage of solvent-free processing allowing highly complex multi-junction architectures similar to inorganic solar cells. This work aims to combine the benefits of both by depositing conjugated polymers using vacuum thermal evaporation. By employing this unconventional approach it aims to enhance the efficiency of organic photovoltaics through increased complexity of the thin-film architecture while improving the nanoscale morphology control of the individual active layers. The thesis explores the vacuum thermal deposition of polythiophenes, mainly poly(3-hexylthiophene) (P3HT) and side-group free poly(thiophene) (PTh). A variety of chemical techniques, such as NMR, FT-IR, GPC, DSC and TGA, are used to examine the effect of heating on chemical structure of the polymers. Optimal processing parameters are identified and related to the resulting thin-film morphology and charge transport properties. Efficient photovoltaic devices based on polythiophene donors and fullerene acceptors are fabricated. Materials science techniques AFM, XRD, SEM, TEM and MicroXAM are used to characterize topography and morphology of the thin films, and UV-Vis, EQE, I-V and C-V measurements relate these to the optical and electronic properties. The results of the study show that polymer side groups have a strong influence on molecular packing and charge extraction in vacuum-deposited polymer thin films. Unlike P3HT, evaporated PTh forms highly crystalline films. This leads to enhanced charge transport properties with hole mobility two orders of magnitude higher than that in P3HT. The effect of molecular order is demonstrated on polymer/fullerene planar heterojunction solar cells. PTh-based devices have significantly better current and recombination characteristics, resulting in improved overall power conversion efficiency (PCE) by 70% as compared to P3HT. This confirms that the chemical structure of the molecule is a crucial parameter in deposition of large organic semiconductors. It is also the first-ever example of vacuum-deposited polymer photovoltaic cell. Next, vacuum co-deposited PTh:C60 bulk heterojunctions with different donor-acceptor compositions are fabricated, and the effect of post-production thermal annealing on their photovoltaic performance and morphology is studied. Co-deposition of blended mixtures leads to 60% higher photocurrents than in thickness-optimized PTh/C60 planar heterojunction counterparts. Furthermore, by annealing the devices post-situ the PCE is improved by as much as 80%, achieving performance comparable to previously reported polythiophene and oligothiophene equivalents processed in solution and vacuum, respectively. The enhanced photo-response is a result of favourable morphological development of PTh upon annealing. In contrast to standard vacuum-processed molecular blends, annealing-induced phase separation in PTh:C60 does not lead to the formation of coarse morphology but rather to an incremental improvement of the already established interpenetrated nanoscale network. The morphological response of the evaporated PTh within the blend is further verified to positively differ from that of its small-molecule counterpart sexithiophene. This illustrates the morphological advantage of polymer-fullerene combination over all other vacuum-processable material systems. In conclusion, this processing approach outlines the conceptual path towards the most beneficial combination of solution/polymer- and vacuum-based photovoltaics. It opens up a fabrication method with considerable potential to enhance the efficiency of large-scale organic solar cells production.

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by Xiao-Ping Cao.
Thesis (Ph.D.)--Chinese University of Hong Kong, 1996.
Includes bibliographical references (leaves 119-126).
Acknowledgement --- p.i
Contents --- p.ii
List of Schemes --- p.iv
List of Tables and Figures --- p.v
List of Spectra --- p.vi
Abstract --- p.ix
Chapter Chapter 1. --- Introduction --- p.1
Chapter Chapter 2. --- "1,2,3-Butatrienes"
Chapter 2.1. --- "Preparation of 1,2,3-Butatrienes" --- p.4
Chapter 2.2. --- Our Synthetic Approach --- p.9
Chapter 2.3. --- Results and Discussion --- p.10
Chapter Chapter 3. --- "1,3,5-Hexatrienes"
Chapter 3.1. --- "Preparation of 1,3,5-Hexatrienes" --- p.16
Chapter 3.2. --- Results and Discussion
Chapter 3.2.1. --- Preparation of Hexatrienes Using the Ramberg-Backlund Reaction --- p.24
Chapter 3.2.2. --- Preparation of Stereoisomerically Pure Diallylic Sulfides and Sulfones --- p.29
Chapter 3.2.3. --- The Stereochemistry of the Ramberg-Backlund Rearrangement of Diallylic Sulfones --- p.34
Chapter 3.2.4. --- Effect of Solvent and Temperature on the Stereochemistry of the Newly Formed Double Bond --- p.38
Chapter 3.2.5. --- Total Synthesis of Galbanolenes --- p.39
Chapter 3.3. --- Conclusions --- p.41
Chapter Chapter 4. --- Enediynes
Chapter 4.1. --- "Preparation of 3-Ene-l,5-diynes" --- p.42
Chapter 4.2. --- Results and Discussion --- p.48
Chapter Chapter 5. --- "1,3,5,7-Octatetraenes"
Chapter 5.1. --- "Preparation of 1,3,5,7-Octatetraenes" --- p.53
Chapter 5.2. --- "Preparation of 1,3,5,7-Octatetraenes Using the Ramberg-Backlund Reaction" --- p.57
Experimental --- p.64
References --- p.119
List of Publications Based on Research Reported in This Thesis --- p.127
Spectra --- p.128

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Abstract:

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009.
Title from title screen (site viewed March 2, 2010). PDF text: xii, 86 p. : ill. (some col.) ; 9 Mb. UMI publication number: AAT 3386756. Includes bibliographical references. Also available in microfilm and microfiche formats.

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Chapter 1 discusses the purpose, the design, and the syntheses of new potential electronic devices. Based on previous and current studies, new oligo(phenylene ethynylene)s containing pyridyl alligator clips have been synthesized for molecular electronics using a series a palladium-catalyzed couplings. Although the testing of these devices is still pending, these devices are expected to show negative differential resistance and molecular memory properties due to their electron-withdrawing nature.Chapter 2 describes the thermal analysis testings of several molecular electronics candidates to gain insight about their suitability for a new hybrid molecular/solid-state approach using chemical vapor deposition process.Chapter 3 depicts the synthesis of new amphiphilic molecules containing a free radical and a carboxylic group as potential devices for quantum computing. These candidates have been tested on silver surface to assess their chemical integrity when self-assembled as a monolayer.Chapter 4 discusses the synthesis of an array of 2 nm-tall anthropomorphic conjugated molecules, the NanoKids, in the monomeric, dimeric and polymeric forms and the use of them in an educational outreach project as 3D animated models to teach science in selected schools. These molecules are called, as a class, NanoPutians.Finally, chapter 5 discusses the synthesis and the challenges of devising an army of NanoKids moving on a surface.