Polyzyklische organische Moleküle und deren Derivate sind eine Klasse von Nanostrukturen, die wegen diverser möglicher Anwendungen in molekularer und organischer Elektronik viel Aufmerksamkeit in der Wissenschaft erregt haben. Um ihre einzigartigen Eigenschaften in vollem Umfang auszunutzen, muss man das Verhalten von molekularen Systemen auf der Nanoskala verstehen und eine Reihe von Herstellungsverfahren entwickeln. In dieser Arbeit werden molekulare Nanostrukturen durch den Bottom-Up-Ansatz der Oberflächensynthese erzeugt. Als Untersuchungsmethode gilt Rastertunnelmikroskopie (STM) bei tiefen Temperaturen und im Ultrahochvakuum als Werkzeug der Wahl. Drei verschiedene molekulare Systeme werden ausführlich erforscht, mit dem Ziel organische Nanostrukturen mit gewünschten Eigenschaften und atomarer Präzision zu erzeugen. Im ersten Teil dieser Arbeit wird eine Cyclodehydrierungsreaktion erfolgreich für die Synthese von asymmetrischen Starphen verwendet. Es wird dann gezeigt, dass dieses Molekül als unimolekulares NAND-Logikgatter fungieren kann. Dabei wird die Positionierungsänderung der elektronischen Resonanz nach der Zufügung einzelner Goldatome an die Inputs des Moleküls gemessen. Eine Kombination aus atomarer und molekularer Lateralmanipulation mithilfe der Spitze des Rastertunnelmikroskops sowie Rastertunnelspektroskopie wird verwendet, um dieses Verhalten zu demonstrieren. Die steuerbare Verschiebung von molekularen Resonanzen entsteht wegen der asymmetrischen Form des Starphens und wurde theoretisch vorhergesagt. Molekulare Drähte werden im zweiten Teil der Arbeit durch die oberflächenassistierte Ullmann-Kupplung hergestellt. Ihr Baustein besteht aus abwechselnden Donor- und Akzeptorgruppen und wurde speziell vorgesehen, um leitfähige flexible molekulare Drähte herzustellen. Die Leitfähigkeit wird durch Ziehen einzelner Drähten von der Oberflächen mit der STM-Spitze gemessen. Theoretische Berechnungen der komplexen Bandstruktur der molekularen Drähte bestätigen die experimentellen Ergebnisse und unterstützen dabei die Wichtigkeit der Balance zwischen Akzeptor- und Donorgruppen für die Leitfähigkeit der Drähte. Basierend auf diesen Resultaten werden neue Strukturen zur Herstellung vorgeschlagen. Der letzte Teil befasst sich schließlich mit einer unimolekularen Reaktion, die zur Erzeugung einer anomalen Kombination von Pentagon- und Heptagonringen in einem einzelnen organischen Molekül führt. Solche 5-7-Einheiten sind analog zu Stone-Wales-Defekten in Graphen und können elektronische Eigenschaften beachtlich ändern. Die exakte intramolekulare Struktur der Reaktionsprodukte wird durch hochauflösende STM-Bildgebung mit funktionalisierter Spitze eindeutig zugeordnet und zusätzlich durch DFT-Rechnungen bestätigt. / Polycyclic organic molecules and their derivatives present the class of nanostructures that are currently in the focus of scientific research due to their perspectives for the versatile applications in molecular and organic electronics. To exploit their unique properties to full extent, one has to understand the behavior of molecular systems at the nanoscale and to develop a set of fabrication methods. In this work, molecular nanostructures are fabricated using the bottom-up on-surface synthesis approach, which allows precision of the desired products and control over their properties through careful precursors design. To study the reaction flow and the properties of the formed structures, scanning tunneling microscopy (STM) at low temperature and in ultra-high vacuum is the tool of choice. In this work, three molecular systems are studied in detail, with the focus of fabricating atomically precise nanostructures with tailored properties. A cyclodehydrogenation reaction is successfully applied to synthesize an asymmetric starphene molecule in the first part of the work. It is then shown that this molecule can function as a unimolecular NAND logic gate with its response to the attached single Au atoms measured as the position of the electronic resonance. A combination of the atomic and molecular lateral manipulation with the STM tip and scanning tunneling spectroscopy (STS) is used to demonstrate this behavior. The effect of the controllable shifting of the molecular resonances is due to the asymmetric shape of the starphene molecule and was initially predicted theoretically. More complex structures, molecular wires, are presented in the second part of the work by using the surface-assisted Ullmann coupling reaction. The monomer unit, consisting of the alternant donor and acceptor parts, was specifically designed to achieve highly-conductive flexible molecular wires. The conductance is measured by pulling the single wires with the STM tip off the surface. Theoretical calculations of the complex band structure of the wires confirm the obtained results and support the discussion of the importance of the balance between the strength of acceptor and donor units for the conductance of the resultant wires. Based on this, some model structures are proposed. Finally, the last part deals with a unimolecular reaction to create an anomalous combination of pentagon and heptagon rings in a single organic molecule. Such 5-7 moieties are analogous to the Stone-Wales defects in graphene and may significantly alter the electronic properties. The precise intramolecular structure of the reaction products is unambiguously assigned by high-resolution STM imaging with functionalized tips and further confirmed by DFT calculations.

The development of new electronic devices requires the design of novel materials since the existing technologies are not suitable for all applications. In recent years, semiconducting polymers (SCPs) have evolved as fundamental components for the next generation of costumer electronics. They provide interesting features, especially flexibility, light weight, optical transparency and low-cost processability from solution. The research presented in this thesis was devoted to theoretical studies of donor-acceptor (DA) copolymers formed by electron-deficient 3,6-(dithiophene-2-yl)-diketopyrrolo[3,4-c]pyrrole (TDPP) and different electron-rich thiophene compounds. This novel type of SCPs has received a lot of attention due to experimental reports on very good electronic properties which yielded record values for organic field-effect transistor applications. In order to get a deeper understanding of the structural and electronic properties, the main objective of this work was to study this material type on the atomic scale by means of electronic structure methods. For this, density functional theory (DFT) methods were used as they are efficient tools to consider the complex molecular structure. This work comprises three main parts: a comparative study of the structural and the electronic properties of TDPP based DA polymers obtained by means of different theory levels, the calculation of the intermolecular charge transfer between pi-pi stacked DA polymer chains based on the Marcus transfer theory and investigations of molecular p-doping of TDPP based DA polymers. For the first, DFT using different functionals was compared to the density functional based tight binding (DFTB) method, which is computationally very efficient. Although differences in structural properties were observed, the DFTB method was found to be the best choice to study DA polymers in the crystalline phase. For the second, correlations between the molecular structure and the reorganization energy are found. Moreover, the dependency of the electronic coupling element on the spatial shape of the frontier orbitals is shown. Furthermore, a Boltzmann-type statistical approach is introduced in order to enable a qualitative comparison of different isomers and chemical structures. For the last part, the p-doping properties of small, multi-polar dopant molecules with local dipole provided by cyano groups were investigated theoretically and compared with experimental observations. The one with the strongest p-doping properties was studied in this work for the first time on a theoretical basis. Comparing these different p-dopants, rich evidence was found supporting the experimentally observed doping strength.

Organic semiconducting polymers are widely employed in organic electronics such as organic photovoltaics (OPVs), organic field-effect transistors (OFETs) and organic light emitting diodes (OLEDs). Their remarkable mechanical and charge transport properties as well as solution processability allow low-cost fabrication of light-weight and flexible devices. Among them indacenodithiophene (IDT)-based materials are promising candidates for application in organic electronics. Due to their low energetic disorder, extended conjugation and high electron density the IDT-based polymers show high field-effect mobilities and high absorption coefficients. However, their synthesis suffers from long reaction sequences and is often accomplished using toxic materials. Commercialization requires development of more efficient and sustainable reaction pathways to ease tailoring of structures and to limit molecular defects. Herein, the development of new synthetic pathways towards IDT-based polymers is presented in which all C-C coupling steps are achieved by C-H activation – an atom-economic alternative to conventional transition-metal catalyzed cross couplings. Two different strategies were established to synthesize a series of well-defined IDT-based homo- and copolymers with different side chain patterns and varied molecular weights. The first way starts by synthesis of a precursor polymer and subsequent cyclization affording IDT homopolymers. In the second approach, cyclized IDT monomers were prepared first and then polymerized using direct arylation polycondensation (DAP) yielding IDT homo- and copolymers. The synthetic pathways were optimized in terms of maximizing molecular weights and limiting defect structures. While the first pathway enables synthesis of well-defined homopolymers, the latter is the method of choice for preparation of IDT-based copolymers in high yields and adjustable molecular weights. The polymers were further characterized in detail by optical, thermal, electrical and morphological analyses. OFETs as well as all-polymer solar cells (all-PSCs) were fabricated to investigate the influence of structural modifications and molecular weight on their optoelectronic performance. Thus, this thesis provides a comprehensive study of the structure-property correlations of IDT-based polymers and simplified synthetic protocols for the design and preparation of donor-acceptor copolymers in the future.

Die Entwicklung optoelektronischer Geräte wurde stark durch organische Donor-Akzeptor-Komplexe beeinflusst, die eine zentrale Rolle in der modernen Optoelektronik spielen. Diese Materialien ermöglichen ein komplexes Zusammenspiel elektronischer, optischer und phononischer Eigenschaften. Frühe Arbeiten zu konjugierten Polymeren in OLEDs und Bulk-Heterojunktionen in organischen Photovoltaikzellen legten das Fundament für praktikable OLEDs und verbesserten die Effizienz in OPVs. Kürzlich hat sich das Forschungsfeld auf hybride anorganisch-organische Systeme ausgeweitet. Diese Materialien kombinieren die hohe Ladungsträgerdichte und -mobilität der anorganischen Komponenten mit den Lichtausbeute- und Emissionscharakteristika organischer Moleküle. Die Integration von Übergangsmetall-Dichalcogenid-Monoschichten hat bedeutende Fortschritte gebracht, besonders für die Feineinstellung der Ladungstransferdynamik. Diese Entwicklungen stellen neue Herausforderungen dar, insbesondere bei der Modellierung laserinduzierter, ultraschneller Ladungstransferdynamik. RT-TDDFT hat sich als effizientes und genaues Werkzeug erwiesen, das für die Untersuchung großer Systeme geeignet ist und die Simulation zeitaufgelöster Phänomene ermöglicht. Diese Dissertation analysiert die laserinduzierte Ladungstransferdynamik in vollständig organischen und hybriden anorganisch-organischen Grenzflächen. Sie untersucht die Komplexität stark und schwach gebundener Grenzflächen und deren Verhalten unter externen Laserpulsen sowie den Temperatureffekten auf die Ladungstransferdynamik. Die Nutzung von RT-TDDFT zur Modellierung ultraschneller Elektronendynamik und vibronischer Kopplung hat das Verständnis in diesem Feld vertieft und die Effektivität bei der Modellierung optoelektronischer Geräte demonstriert. / The development of optoelectronic devices has been significantly influenced by organic donor-acceptor complexes, which play a central role in modern optoelectronics. These materials enable a complex interplay of electronic, optical, and phononic properties. Early work on conjugated polymers in OLEDs and bulk heterojunctions in organic photovoltaic cells laid the foundation for practical OLEDs and improved efficiency in OPVs. Recently, the field of research has expanded to hybrid inorganic-organic systems. These materials combine the high charge carrier density and mobility of inorganic components with the light yield and emission characteristics of organic molecules. The integration of transition metal dichalcogenide monolayers has brought significant advances, particularly in fine-tuning charge transfer dynamics. These developments present new challenges, especially in modeling laser-induced, ultrafast charge transfer dynamics. RT-TDDFT has proven to be an efficient and accurate tool suitable for studying large systems and enabling the simulation of time-resolved phenomena. This dissertation analyzes the laser-induced charge transfer dynamics in fully organic and hybrid inorganic-organic interfaces. It investigates the complexity of strongly and weakly bound interfaces and their behavior under external laser pulses, as well as the temperature effects on charge transfer dynamics. The use of RT-TDDFT to model ultrafast electron dynamics and vibronic coupling has deepened the understanding in this evolving field and demonstrated its effectiveness in modeling optoelectronic devices.

Une nouvelle famille de précatalyseurs à base d'lr(lll) a été découverte. La facilité de leur préparation, leur remarquable stabilité, et surtout leur excellente efficacité catalytique dans plusieurs réactions, c.-à-d. la 0-silylation d'alcools, l'hydrosilylation de fonctions CO et CN et l'activation de la liaison C-F, constituent un ensemble de propriétés que d'autres précatalyseurs organométalliques similaires connus à ce jour ne possèdent pas. Le fait le plus significatif est la mise en évidence expérimentale et théorique que les espèces catalytiques impliquées fonctionnement comme une paire de Lewis du type donneur-accepteur [lr(lll)H]-->[SiR3]. Dans ce cas le ligand silylium doit être considéré comme un ligand Z en appliquant le formalisme de Green, ce qui suggère un état d'oxidation formel de +Ill pour l'atome d'iridium. Cette thèse a contribué à une meilleure compréhension de la chimie du silylium appliquée à la chimie organométallique, et a abouti à l'émergence d'un nouveau champ de recherche qui pourra permettre l'élaboration de nouveaux précatalyseurs multicompétents. / A new family of highly active iridacyclic lr(lll) precatalysts has been discovered. Notably, these ionic iridacycles are very stable so that their handling under air whether in solution or as solid powder is possible. The relative simplicity of their molecular structures allows their preparation on gram scale through a very simple and convenient synthetic protocol. We identified important iridium-silane intermediates involved in the catalysis of various reactions, e.g. the 0-silylation of alcohols, the hydrosilylation of CO and CN functions, and the activation of the C(sp3)-F bond of fluorocarbons. Experimental and theoretical studies of these intermediates point towards a Lewis donor-acceptor structural formulation of the type [lr(lll)H]-->[SiR3]. These results constitute a significant contribution to the design of future multicompetent precatalysts, and provide an original insight to the bonding within the Si-lr-H motif by considering the silylium ion [SiR3]+ as a Z-type ligand rather than a "traditional" X ligand.

The homo and hetero dimerisation of two spectroscopically different chromophores were studied, namely: 4,4-difluoro-4-bora-3a,4a-diazas-indacene (g-BODIPY) and its 5-styryl-derivative (r-BODIPY). Various spectroscopic properties of the r-BODIPY in different common solvents were determined. It was shown that g- and r-BODIPY in the ground state can form homo- as well as hetero dimers. We demonstrate that the ganglioside GM1 in lipid bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) exhibits a non-uniform lateral distribution, which is an argument in favour of self-aggregation of GM1 being an intrinsic property of the GM1. This was concluded from energy transfer/migration studies of BODIPY-labelled gangliosides. An algorithm is presented that quantitatively accounts for donor–donor energy migration (DDEM) among fluorophore-labelled proteins forming regular non-covalent polymers. The DDEM algorithm is based on Monte Carlo (MC) and Brownian dynamics (BD) simulations and applies to the calculation of fluorescence depolarisation data, such as the fluorescence anisotropy. Thereby local orientations, as well as reorienting motions of the fluorescent groups are considered in the absence and presence of DDEM among them. A new method, in which a genetic algorithm (GA) was combined with BD and MC simulations, was developed to analyse fluorescence depolarisation data collected by the time-correlated single photon counting technique. It was applied to study g-BODIPY-labelled filamentous actin (F-actin). The technique registered the local order and reorienting motions of the fluorophores, which were covalently coupled to cysteine 374 (C374) in actin and interacted by means of electronic energy migration within the polymer. Analyses of F-actin samples composed of different fractions of labelled actin molecules revealed the known helical organiszation of F-actin, and demonstrated the usefulness of this technique for structure determination of complex protein polymers. The distance from the filament axis to the fluorophore was found to be considerably less than expected from the proposed position of C374 at a high filament radius. In addition, polymerisation experiments with BODIPY-actin suggest a 25-fold more efficient signal for filament formation than pyrene-actin.

The present thesis is focused on the rational design of Diketopyrrolopyrrole based π- conjugated polymers for organic electronics. The thesis is organized into six different chapters and a brief description of the individual chapters is provided below. Chapter 1 briefly describes the physics governing the electronic processes occurring in organic photovoltaics (OPVs) and organic field-effect transistors (OFETs) followed by design rules for the synthesis of conjugated polymers for organic electronics. Diketopyrrolopyrrole (DPP) based π-conjugated materials and their development in OPVs and OFETs have been highlighted. Chapter 2 discusses the synthesis and characterization of a series of small molecules of DPP derivatives attached with different alkyl chains. Influence of side chains on the photophysical properties of these DPP derivatives have been studied by UV-visible spectroscopy and DFT calculations. Crystal structure studies revealed the effect of alkyl chains on the torsional angle, crystal packing, and intermolecular interactions such as π-π stacking. Chapter 3 reports the synthesis of novel diketopyrrolopyrrole-diketopyrrolopyrrole (DPPDPP) based conjugated copolymers and their application in high mobility organic field-effect transistors. Effect of insulating alkyl chains on polymer thin film morphology, lamellar packing and π-π stacking interactions have been studied in detail. Investigation of OFET performance of these DPP-DPP copolymers with branched alkyl chains (N-CS2DPP-ODEH) resulted in low charge carrier mobilities as compared to the polymers (N-CS2DPP-ODHE) with linear alkyl chains. Polymer with triethylene glycol side chains (N-CS2DPP-ODTEG) exhibited a high field-effect electron mobility value of ~3 cm2V-1s-1 with a very low threshold voltage of ~2 V. Chapter 4 investigates the effect of torsional angle on the intermolecular interactions and charge transport properties of diketopyrrolopyrrole (DPP) based polymers (PPDPP-OD-HE and PPDPP-OD-TEG). Grazing incidence x-ray diffraction studies shows the different orientation of the polymer crystallites and lamellar packing involved in polymer thin films. Investigation of OFETs evidenced the effect of torsional angle on the charge transport properties where the polymer with higher torsional angle PPDPP-OD-TEG resulted in high threshold voltage with less charge carrier mobility compared to the polymer with lower torsional angle (N-CS2DPP-OD-TEG). Chapter 5 investigates the effect of photoactive material morphology on the solar cell device performance, and charge transfer kinetics by adding high boiling point processing additives. DPP based donor-acceptor (D-A) type low band gap polymers (PTDPPQ and PPDPPQ) have been synthesized and employed in bulk-heterojunction (BHJ) solar cells with the acceptor PC71BM. Addition of processing additive 1,8-diiodooctane (DIO) resulted in three order improvements in power conversion efficiency (PCE). Chapter 6 describes the design and synthesis of two diketopyrrolopyrrole based copolymers (PPDPP-BBT and PTDPP-BBT) for their application in organic devices such as field-effect transistors and bulk-heterojunction solar cells. Investigation of OFET performance of these DPP based copolymers displayed hole mobilities in the order of 10-3 cm2V-1s-1. The semiconductor-dielectric interface has been characterized by capacitance-voltage, and Raman scattering methods. In summary, the work presented in this thesis describes the synthesis and characterization of diketopyrrolopyrrole based new polymeric semiconductors. Effects of insulating side chains and torsional angle on the charge transport properties of these polymers in OFETs have been investigated. This work also describes the effect of solvent additives on the active layer morphology and BHJ solar cell device performance. The results described here show that these materials have potential application as active components in plastic electronics.

We report the morphological characterization of triisopropylsilylethynyl-dibenzochrysene (TIPS-DBC:PCBM) blends, a bulk heterojunction (BHJ) solar cell system based on a highly crystalline small molecule donor. We found that processing the blends from a volatile solvent such as chloroform is beneficial in controlling the crystal size and phase separation of the donor–acceptor phases. When a less-volatile solvent such as chlorobenzene is used, large crystalline domains formed, exceeding the length scale suitable for BHJ solar cells. When the BHJ films are thermally annealed, enhanced domain purity is observed for the chloroform processed thin films, which led to an increased short circuit current in the devices.

The development of solution-processable semiconducting polymers has brought mankind’s long-sought dream of plastic electronics to fruition. Their potential in the manufacturing of lightweight, flexible yet robust, and biocompatible electronics has spurred their use in organic transistors, photovoltaics, electrochromic devices, batteries, and sensors for wearable electronics. Yet, despite the successful engineering of semiconducting polymers, we do not fully understand their molecular behavior and how it influences their doping (oxidation/reduction) properties. This is especially true for donor-acceptor (D-A) p-systems which have proven to be very efficient at tuning the electronic properties of organic semiconductors. Historically, chain-length dependent studies have been essential in uncovering the relationship between the molecular structure and polymer properties. Discussed here is the systematic investigation of a complete D-A molecular series composed of monodispersed and well-defined conjugated molecules ranging from oligomer (n=3-21) to polymer scale lengths. Structure-property relationships are established between the molecular structure, chain conformation, and redox-active opto-electronic properties for the molecular series in solution. This research reveals a rod-to-coil transition at the 15 unit chain length, or 4500 Da, in solution. The redox-active optical and electronic properties are investigated as a function of increasing chain-length, giving insight into the nature of charge carriers in a D-A conjugated system. This research aids in understanding the solution behavior of conjugated organic materials. <br>

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