L'efficacité des cellules photovoltaïques organiques est influencée par la morphologie du mélange composant la couche active. L'objectif de cette thèse a été d'élaborer un agent compatibilisant pour stabiliser la morphologie du mélange P3HT:PCBM. Nous avons choisi de synthétiser des copolymères alternant motifs C60 et polythiophène pour améliorer la miscibilité entre P3HT et PCBM. Les copolymères ont été réalisés par polycondensation d'un dérivé C60 avec plusieurs oligothiophènes régioréguliers de difonctionnalité contrôlée. Une attention particulière a été accordée aux conditions de polycondensation qui ont été optimisées pour favoriser de hauts degrés de polymérisation. Les caractérisations structurales, optiques et électrochimiques des matériaux ont été réalisées. Leur effet compatibilisant a été évalué en caractérisant la morphologie de la couche active par des mesures en cellules photovoltaïques, des observations par microscopie à force atomique et des calculs d'énergies de surface.

This dissertation focuses on the design, synthesis, and characterization of a variety of organic dyes, semiconducting materials, and surface redox-active modifiers of potential interest to organic-based emerging photovoltaics. A discussion of the materials’ optoelectronic properties, their ability to modify and promote electron transfer through an organic/transparent conducting-oxide interface, and finally their effect on the photovoltaic properties of devices utilizing them as light-harvesters is provided where relevant. The first two research chapters discuss mono-chromophoric asymmetric squaraine-based sensitizers and covalently linked, dual-chromophoric, porphyrin-squaraine sensitizers as light absorbers in dye-sensitized solar cells (DSSCs), in an attempt to address two problems often encountered with DSSCs utilizing this class of near infra-red sensitizers; The lack of panchromatic absorption and aggregation on the surface. Also, this dissertation discusses the design and synthesis of asymmetric perylene diimide phosphonic acid (PDI-PA) redox-active surface modifiers, and reports on the electron-transfer rates and efficiencies across the interface of an ITO electrode (widely used in organic-electronic devices) modified with these perylene diimides. Finally two series of hole-transport materials based on oligothiophenes and benzodithiophenes are reported: optoelectronic properties and preliminary performance of organic photovoltaic (OPV) devices fabricated with them is discussed.

Conjugated polymers and oligomers have been widely studied based on their wide range of useful properties and applications. Given the importance of self-assembly and charge transfer in the development of conjugated materials for use in electronic applications, it is crucial to: (i) prepare functional materials by molecular design, (ii) evaluate the structure-property relationships of new materials, and (iii) develop fundamental understanding of electronic structure and charge transport behavior. The use of conjugated polymeric materials in electronic applications relies on control of the assembly and orientation of the polymer chains in the solid state. Conjugated polymers with liquid crystalline behavior could be used to implement an additional level of control over orientation and resultant properties. Substitution of the conjugated polythiophene backbone with semifluoroalkyl side chains (i.e., the diblock -(CH2)m(CF2)nF) has afforded materials with unusual properties. The mutual immiscibility of the aromatic backbone, the alkyl side-chain segments, and the fluoroalkyl side-chain termini provides control over supramolecular packing. A series of eight polymers has been synthesized, in which the lengths of the alkyl (m) and fluoroalkyl (n) segments are varied. One regiorandom analogue and two poly(3-alkylthiophene)s were also synthesized for comparative purposes. The structure, molecular weight, and regioregularity of the polymers were evaluated using a variety of techniques. The semifluoroalkyl-substituted polymers have been systematically studied to determine the effect of side chain length and m:n block ratios on their solution state, liquid crystalline, and solid state properties. The effect of side chains on conjugation was determined, where solubility allowed, by solution-state UV-visible and fluorescence spectroscopy. The thermal and liquid crystalline properties of the homopolymers were evaluated by DSC, variable-temperature X-ray diffraction, and polarized optical microscopy. Several semifluoroalkyl-substituted polythiophene homologues show liquid crystalline behavior. Molecular packing and charge transport are key factors governing the use of conjugated materials in electronic applications. A wide variety of oligomers have been studied as models for charge migration in conjugated polymers. One-dimensional models do not adequately represent two-dimensional charge transport; thus, a variety of two-dimensional, covalently-linked models have been developed. Previous work by our group, and others, led to the proposal of bis(oligothienyl) compounds as models to study the interaction of the ð-conjugated chains. Previous reports by other researchers described the synthesis and characterization of hydrogen-terminated analogues of 1,8-bis(oligothienyl)naphthalenes. However, these materials proved to be unsuitable for use as charge transport models, as they were subject to irreversible polymerization upon oxidation. Installation of methyl groups at the terminal a-positions of 1,8-bis(oligothienyl)naphthalenes allowed us to create a series of models in which conjugated chains are held in close proximity. This provides access to multiple redox states, and future systems based on these molecules may be used as models for charge transport or as functional materials for incorporation into devices.

The nature of the ground state and the first (lowest) singlet excited state geometrical conformations and electronic transitions in the aromatic five-membered heterocyclic oligomers &ndash / oligothiophenes (nT), oligofurans (nF), and oligopyrroles (nP)- containing up to six monomer units (total of 18 molecules) were explored using several computational methodologies. Geometry optimizations were carried out at Austin Model 1 (AM1), Restricted Hartree-Fock (RHF/6-31G*), and Density Functional Theory (DFT, B3LYP/6-31G*) levels for the ground-state conformations of these structurally well-defined heterocyclic oligomers. The Configuration Interaction Singles (CIS) method with the 6-31G* basis set was chosen in computation of the optimal geometry of the lowest singlet excited state. Lowest singlet excitation S1&szlig / S0 energies were calculated using the Zerner&rsquo / s Intermediate Neglect of Differential Overlap for Spectroscopy (ZINDO/S), CIS (CIS/6-31G*), and Time-Dependent DFT (TDDFT/6-31G* and TDDFT/6-31+G*) methods. In computation of the emission S1&agrave / S0 energies, we have employed all methods above except ZINDO/S. In investigation of geometries of the ground and lowest singlet excited state, we compared the bond length alternation (BLA) parameters, Dri in the conjugated backbone of the oligomers. Saturation of the geometrical parameters at the center of oligomers was observed after a certain chain length. Among all methodologies used in computation of excitation (S1&szlig / S0) and emission (S1&agrave / S0) energies, TDDFT results showed the best agreement with experimental data. Fits of computed and experimental excitation energies to an exponential function using the least squares method enabled us to predict Effective Conjugation Length (ECL) values. We obtained the ECLs of 17 (17), 16 (15), and 14 (13) monomer units for polythiophene (PTh), polyfuran (PFu), and polypyrrole (PPr), which have very good agreement with the results obtained from the fits of experimental data (the values in parentheses).

Triarylborane Functionalized Dicyanovinyl and Acetylacetone Based Molecular Platforms: Building Blocks for Multiple Anion Sensors and Efficient Phosphorescence Emitters The main objective of this thesis is to design a simple strategy for triarylborane based multiple anion sensors and development of triarylborane incorporated phosphorescent metal complexes. The thesis consists of eight chapters and the contents of each chapter are given below. Chapter 1 This chapter gives a general introduction to recent advances relevant to the theme of the thesis. A review of the fundamental characteristics of triarylboranes and their applications in various fields such as chemical sensors and optoelectronics is presented. Advances in boron chemistry in the areas such as anion sensors, solid state emissive and phosphorescence materials are discussed in detail. The scope of the thesis is outlined at the end of the chapter. Chapter 2 The second chapter deals with the general experimental techniques and synthetic procedures followed in this thesis. Chapter 3 This chapter deals with a rational design strategy for differential identification of fluoride and cyanide ions using TAB based sensors. In general, most of the triarylboranes give similar optical responses towards fluoride and cyanide ions as they follow similar sensing mechanism. In order to circumvent this problem, two TAB-DCV conjugates (1 and 2) are designed and synthesised. The DCV unit is highly specific for cyanide ion owing to the presence of electrophilic carbon center. Probes 1 and 2 differ in steric crowding around the boron center. The less crowded boron center in 1 binds with fluoride as well as with cyanide ions giving similar optical response (luminescence is quenched in presence of F¯ and CN¯). In the case of 2, selectivity of boron center towards fluoride is tuned by increasing the steric crowding around the boron unit. The dicyanovinyl unit acts as selective sensing site for cyanide ions. As a result, 2 gives different fluorogenic response towards the anions F¯ and CN¯ which were considered as interfering anions in TAB based sensor chemistry. Thus, a modular design principle is developed for differential identification of fluoride and cyanide ions using TAB. Chapter 4 In this chapter, detailed photophysical studies of TAB-amine-DCV conjugates and colorimetric discrimination of fluoride and cyanide ions are discussed. Presence of amine based donor between the two electron deficient sites enhances the electronic conjugation in 3−5. Since there are two different acceptor sites with a common donor, two distinct charge transfer transition bands are observed in the visible region of electromagnetic spectrum. The absorption and emission spectra of these compounds show pronounced sensitivity to solvent polarity, signifying large excited state dipolmonents. Anion binding studies confirms that these compounds are highly selective towards fluoride and cyanide ions. Fluoride ions selectively interact with boron center and block the corresponding charge transfer transition thereby leading to a distinct colour change which is observable by naked eye. On the other hand, cyanide interacts with boron as well as DCV unit and blocks both the charge transfer transitions which results in disappearance of colour. Hence, compounds 4 and 5 exhibit different colorimetric signals for fluoride and cyanide ions. Since the absorption bands of 3 do not fall in the visible region, it does not show any colorimetric response towards the aforementioned anions. The anion sensing mechanisms are established by 1H, and 19F NMR studies. Chapter 5 This chapter presents a systematic study of the effect of length of π-electronic conjugation on the optical properties and anion sensing abilities of a series of TAB-oligothiophene-DCV conjugates (6−8). Their absorption as well as emission bands undergo redshift upon increasing the number of thiophene units between TAB and DCV units as the π-electronic conjugation in 6−8 is greatly dependent on the number of thiophene units. Their fluorescence emission is highly sensitive to solvent polarity. In the case of 6, the emission band undergoes a redshift with reduced intensity. In the case of 7 the emission band undergoes a redshift but the intensity is not affected by solvent polarity. In the case of 8, the emission band undergoes redshift with enhanced intensity in polar solvents. Interestingly, 7 and 8 show solvent viscosity dependent fluorescence. Structural reorganisation is restricted in viscous medium and results in enhanced emission for 7 and 8. Further, these compounds exhibit selective response towards the fluoride and cyanide ions with different colorimetric responses. Test strips made up of probes 7 and 8 have potential application in identifying fluoride and cyanide ions in aqueous medium. Chapter 6 This chapter describes synthesis and optical characterisation of triarylborane incorporated acetylacetone (acacH) ligands (9, 10) and their borondifluoride complexes (11, 12). AcacH ligands and BF2 complexes show solvent dependent emission phenomena due to the involvement of charge transfer transition. Their optical properties are highly dependent on molecular conformations. Complex with duryl spacer (12) exhibits more red shifted emission in polar solvents due to the enhanced charge transfer transition facilitated by twisted rigid geometry. In presence of fluoride and cyanide ions, the borondifluoride complexes are not stable. The anions concomitantly interact with tricoordinate boron as well as acac-BF2 unit to give rise to complex pattern of photoluminescence spectral changes during the titration experiment. The binding pathway and the possible species involved are established with the help of 1H, 19F and 11B NMR spectral studies in presence of the anions. Complexes 11 and 12 act as selective chemodosimetric sensors for fluoride and cyanide ions. Chapter 7 In this chapter, the synthesis and optical characterisations of triarylborane conjugated cyclometalated platinum complexes are discussed. A series of square planar platinum complexes are synthesised with different cyclometalating ligands. Complexes (13−18) exhibit a range of luminescence from green to red in solution as well as in the solid state. Their emission intensities are highly sensitive towards atmospheric oxygen suggesting that they originate from a triplet excited state. A maximum of 85% quantum yield is observed for complex 15 in solution state while complex 14 showed a maximum of 58% quantum yield in solid state. Complexes with rigid molecular conformation (14, 16 and 18) showed higher luminescence quantum yield than those having phenyl spacer (13, 15 and 17). The sterically encumbered boryl (-BMes2) group significantly reduces π-π stacking between the square planar entities. Thus, complexes 13−18 show bright luminescence in solid state compared to model complexes without boryl group. The effect of Lewis acidic boron center on luminescence behaviour is explored by fluoride binding studies. Chapter 8 This chapter is divided into two parts. Part-I describes the synthesis and optical characterisation of triarylborane conjugated cyclometalated iridium complexes (19−24). They are brightly luminescent in solution state with high sensitivity towards atmospheric oxygen. Complex 20 shows a highest quantum yield of 91%. Interestingly, under ambient atmospheric conditions, they exhibit a rare type of dual emission. Life time data suggest that the lower energy emission band originates from cyclometalated iridium based triplet excited state while higher energy emission band originates from boryl ased singlet excited state. Fluoride binding at the boron site results in luminescence quenching; evidently, tri-coordinate boron has a major contribution to the luminescence features of these iridium complexes. Part-II deals with synthesis of triarylborane conjugated pyrazole ligand (25) and its binuclear iridium complexes (26−28) in which two iridium centers are bridged by hydroxo as well as pyrazolato ligands. These binuclear iridium complexes exhibit higher luminescence quantum yield than TAB-acac-Iridium complexes (mononuclear complexes; part I). Binding of fluoride ions at the boron center has a minor impact on their luminescence nature. High sensitivity of their luminescence towards atmospheric oxygen indicates the involvement of triplet excited state in their emission process.

L'électronique plastique est devenue en une dizaine d'années un domaine actif, tant en recherche fondamentale qu'en application. La compréhension et le contrôle des forces motrices du transport ambipolaire est un objectif clé de la recherche dans le domaine de l'électronique organique, et plus particulièrement des transistors. Après une introduction rappelant les principes des transistors organiques ambipolaires et un état de l'art du domaine, les outils et méthodes utilisés au cours de ce travail ont été présentés. Le premier chapitre présente les résultats obtenus des transistors réalisés par évaporation sous vide de phtalocyanines de cuivre. Dans un premier temps la stabilité et les performances des deux semi-conducteurs isolés ont été caractérisés, puis une étude morphologique, électrique et structurelle a été menée sur des dispositifs en structure bicouche ou interpénétrée. Le deuxième chapitre présente une nouvelle méthode d'élaboration de transistors : le LIFT (LAser Induced Forward Transfer). Les premiers transistors à canal p et n'ont ainsi été réalisés à base de phtalocyanines de cuivre, avant de tenter d'obtenir des dispositifs ambipolaires. Cette méthode récente peut permettre de déposer des films à une très grande cadence menant à des dispositifs microstructurés de grande précision. Le dernier chapitre présente une approche par voie liquide. Des solutions de DH-DS2T et PDIF-CN2 ont été élaborées afin de réaliser des encres par le mélange de ces deux solutions pour être déposées par tournette ou dépôt par goutte. en conclusion, les différentes méthodes sont évaluées et comparées afin de déterminer leur utilité et applicabilité respectives. / During the past decade, plactic electronics has become an active research domain, both fundamental and application side. Undestanding and controling the phenomenom which rule the ambipolar transport is one of the main aims of research in organic electronics and transistors. After an introduction giving the principles and a state of the art of organic ambipolar transistors, materials and methods used are described. The first chapter deals with the results obtains whith transistors based on copper phtalocyanines elaborated by a vacuum evaporation process. Stability is isolated moieties was first investigated. Then, morphology, performance and structure of bilayer and blend systems. The second chapter presents the results obtained for transistors elabored by LIFT (Laser Induced Forward Transfer). The first n-channel and p-channel transistors elabored by laser deposition were obtained from copper phtalocynanines. Then the possibility to obtain ambipolar decives was investigated. This brand new technology can permit to create microstructures with a great deposition velocity. The last chapter presents the liquid way approach. DH-DS2T and PDIF-CN2 solutions were used to realise link by mixing the two solutions. those ink where deposited by drop-cast or spin-coating. Finally, the different methods used in this work were evaluated and compared in order to define their usefulness and applicability

In organischen Solarzellen resultiert die photovoltaische Aktivität aus dem das Sonnenlicht absorbierenden Donor-Akzeptor-Heteroübergang. Die Grenzfläche zwischen den beiden organischen Materialien dient der effizienten Ladungsträgertrennung. Die vorliegende Arbeit leistet einen Beitrag im Verständnis zum Wirkungsmechanismus und der zu optimierenden Parameter in diesen Solarzellen. In Bezug auf die Anpassung des Donor-Akzeptor-Heteroübergangs wird neben dem Mechanismus der Ladungsträgergeneration an der Grenzfläche die erzielbare Leerlaufspannung in den Solarzellen diskutiert. Ein wesentliches Kriterium zur Erhöhung der Leerlaufspannung ist die Anpassung der Energieniveaus am Heteroübergang. Eine effiziente Ladungsträgertrennung wird durch eine hinreichende Stufe im Ionisationspotenzial sowie in der Elektronenaffinität am Heteroübergang erreicht. Zur Maximierung der Leerlaufspannung muss diese Überschussenergie, d.h. die Energiedifferenz zwischen photogeneriertem Exziton und freiem Ladungsträgerpaar, auf das notwendige Minimum reduziert werden. Eine Reihe von Dicyanovinyl-Oligothiophenen (DCVnT, n=3-6) wurden als Donor im Heteroübergang zu Fulleren C60 verwendet. Das Ionisationspotenzial der DCVnT nimmt mit zunehmender Kettenlänge ab, während die Elektronenaffinität, die weitestgehend durch die Dicyanovinyl-Endgruppen bestimmt wird, von der Kettenlänge nahezu unabhängig ist. Mittels photoinduzierter Absorptionsspektroskopie und zeitaufgelöster Fluoreszenzmessung wurde der Energie- und Elektronentransfer zwischen DCVnT und C60 entlang der homologen Reihe der DCVnT untersucht. Eine wesentliche Feststellung ist die Korrelation zwischen Rekombination in den Triplettzustand und der Leerlaufspannung. So konnte unter anderem gezeigt werden, dass durch die Verwendung angepasster Heteroübergänge unter bestimmten energetischen Voraussetzungen die indirekte Triplettbesetzung einen bislang nicht beachteten Verlustmechanismus für organische Solarzellen darstellt. Für organische Solarzellen ist demnach ein Kompromiss zwischen möglichst hoher Leerlaufspannung und effizienter Ladungsträgerdissoziation unter Vermeidung dieser Triplettrekombination zu erzielen. Weiterhin wird ein Konzept zur Nutzung dieser indirekten Triplettrekombination diskutiert. Dieses basiert auf der Tatsache, dass die Lebensdauer der Exzitonen im Triplettzustand gegenüber denen im Singulettzustand um 3-6 Größenordnungen höher ist. Damit wird eine höhere Diffusionslänge erwartet, was in einer dickeren und damit stärker absorbierenden aktiven Schicht genutzt werden könnte.

Dans ce manuscrit est décrite l'utilisation d'interactions supramoléculaires pour diriger l'auto-assemblage de composés donneurs et accepteurs d'électrons au sein de dispositifs photovoltaïques organiques. Dans ce but, des matériaux de type oligo-3-hexylthiophène et fullerène ont été fonctionnalisés avec des groupements de reconnaissance complémentaires mélamine – acide barbiturique. La présence de élements solubilisants confère à ces composés une bonne mise en oeuvre permettant la fabrication de dispositifs photovoltaïques à hétérojonction volumique. L'effet de la composition et du post-traitement de la couche active sur la performance de ces dispositifs ont été explorés. Les études de mobilité de charge et des mécanismes de recombinaison au sein de ces matériaux indiquent que l'équilibre entre auto-association et séparation de phases est crucial pour l'efficacité en conversion photovoltaïque. / This research aims to elucidate the use of supramolecular interaction to guide the formation of well-defined nanoscale self-assembled architecture in photovoltaic solar cells as a means to improve device efficiency. Complementary molecular recognition sites based on melamine and barbituric acid were used to obtain functionalized fullerene and oligothiophene materials with superior processibility thanks to the presence of specific solubilizing groups. The efficiency of solid-state devices fabricated using the bulk heterojunction design was studied with respect to device morphology and composition. Experiments on recombination mechanism and field effect mobilities suggest that the balance between hydrogen-bonding interactions induce self-assembly and p-p interactions to promote phase segregation is crucial to the micro-structure of the active layer. The investigated of the relationship between the oligothiophene chain size and various complementary hydrogen-bonding motifs is envisaged.

Key issues in improving small molecule organic solar cells (SMOSC) are the need for new absorber materials and optimized active layer morphology. This thesis deals with the improvement of SMOSC on the donor material side. Promising donor materials (D) are provided by dicyanovinyl endcapped oligothiophenes DCV2-nT (n = 3, . . . , 6) synthesized in the group of Prof. Bäuerle at the University of Ulm. Here, DCV2-nT (n = 3, 5) with different alkyl side chains are characterized. Side chain variations mainly influence the aggregation of molecules in pristine films as well as in blend films with the commonly used acceptor (A) fullerene C60. With changes in the layer morphology, important physical properties in thin film like absorption spectra, energy levels, as well as excited state properties are changed. The focus of this work are excited state properties accessed by photoinduced absorption spectroscopy (PIA). PIA probes the long living excited states in pristine and blend films, i. e. triplet excitons, anions, and cations. For a series of four dicyanovinyl-terthiophenes DCV2-3T (without side chains, with two methyl, two butyl, and four butyl side chains) a systematic study of the effect of alkyl side chains on the aggregation in neat and blend film is discussed. In consequence the efficiency of the energy transfer mechanism between DCV2-3T and C60 is affected. It turns out that in solution spectra and cyclic voltammetry (CV) measurements, the variation of alkyl side chains has almost no influence. However, in thin film there is strong impact on the molecular arrangement confirmed by strongly varying absorption spectra, ionization potentials, and surface roughnesses. Furthermore, PIA measurements reveal that the energy transfer efficiency between D and A in general decreases with increasing side chain length, but is most efficient for a compound with methyl side chains. For blends of dicyanovinyl-quinquethiophenes (DCV2-5T) with C60, the layer morphology is influenced by two different methods. On one hand substrate heating is applied while deposition of the active layer, on the other hand DCV2-5Ts with different alkyl side chains (four methyl and four butyl side chains) are used. Deposition on a heated substrate (80°C) results in an improved solar cell performance, assigned to the formation of a sufficient phase separation of D and A phase in the active layer. This leads to reduced recombination losses and closed percolation paths. The morphological change can be correlated to an increased lifetime of cations. In blends deposited on a heated substrate, the donor cation lifetime increases by almost one order of magnitude from around 10 μs to ≈ 80 μs. This increase of carrier lifetime is both detected optically by PIA as well as electrically by impedance spectroscopy. The increase in lifetime is consequently assigned to a better spatial separation of positive and negative charges induced by the phase separation. Comparing DCV2-5T with methyl and butyl side chains results in a similar effect: The dicyanovinyl-quinquethiophene with methyl side chains leads to an improved solar cell device performance compared to devices comprising the compound with butyl side chains as donor. The improved device performance is again accompanied by an increase in cation lifetime detected by PIA. / Die Entwicklung neuer Absorber-Materialien sowie die Morphologie der photo- aktiven Schicht sind zentrale Themen hinsichtlich der Optimierung organischer Solarzellen aus kleinen Molekülen. In der vorliegenden Arbeit werden diese beiden Aspekte von Seiten des Donor-Materials (D) her behandelt. Die Material- klasse der Dicyanovinyl-Oligothiophene DCV2-nT(n=3,...,6) (synthetisiert in der Arbeitsgruppe von Prof. Bäuerle an der Universität Ulm) dient dabei als Ausgangspunkt. Insbesondere werden DCV2-nT-Moleküle (n = 3, 5) mit verschiedenen Alkyl-Seitenketten charakterisiert. Die Variation der Seitenketten beeinflusst in erster Linie die Anordnung der Moleküle in Einzel- sowie in Mischschichten mit dem typischerweise verwendeten Akzeptor-Material Fulleren C60 (A). Als Folge der Schichtmorphologie ändern sich physikalische Eigenschaften wie u. a. Absorptions- spektren, Energieniveaus sowie die Eigenschaften angeregter Zustände. Angeregte Zustände, wie Triplett-Exzitonen, Anionen und Kationen werden in dieser Arbeit mittels photoinduzierter Absorptionsspektroskopie (PIA) charakterisiert. Anhand einer Serie von vier Dicyanovinyl-Tertiophenen DCV2-3T (ohne Seiten- ketten, mit zwei Methyl-, zwei Butyl-, und vier Butyl-Seitenketten) werden systematisch Einflüsse der Seitenketten auf die Aggregation der Moleküle in Einzel- und Mischschichten untersucht. Besonderes Augenmerk liegt dabei auf dem Effekt der Seitenketten auf den Energie-Transfer-Mechanismus zwischen D und A. In Lösungsmittelspektren und Cyclovoltammetrie-Messungen ist fast keine Änderung durch die Seitenketten erkennbar. Im Dünnfilm hingegen besteht ein starker Einfluss auf die molekulare Anordnung, erkennbar in einer starken Variation der Absorptionsspektren, Ionisationspotentiale und Oberflächen-Topographie. PIA- Messungen zeigen weiterhin, dass im Allgemeinen die Effizienz des Energie-Transfer- Mechanismus mit zunehmender Länge der Alkyl-Ketten abnimmt. Der effizienteste Transfer besteht jedoch für die Verbindung mit Methyl-Seitenketten. In Mischschichten aus Dicyanovinyl-Quinquethiophenen (DCV2-5T) und C60 werden hier zwei Methoden zur Beeinflussung der Schichtmorphologie verfolgt. Zum einen wird die aktive Schicht auf einem geheizten Substrat abgeschieden, zum anderen werden DCV2-5T-Moleküle mit Methyl- und Butyl-Seitenketten als Donor verwendet. Das Abscheiden der aktiven Schicht auf einem geheizten Substrat (80 °C) führt zu einer verbesserten Solarzellenleistung, was auf die Bildung einer hin- reichenden Phasenseparation von D- und A-Phasen in der aktiven Schicht zurückzuführen ist. Die Phasenseparation bewirkt eine Reduktion von Rekombinationsverlusten und die Bildung geschlossener Perkolationspfade. Die morphologische Änderung korreliert mit einem Anstieg der Ladungsträger-Lebensdauer um fast eine Größenordnung von etwa 10 μs auf ≈ 80 μs. Der Anstieg kann sowohl optisch durch PIA, als auch elektrisch mittels Impedanz-Spektroskopie detektiert werden. Eine höhere Lebensdauer der Ladungsträger kann letztlich auf eine größere räumlichen Separation der positiven und negativen Ladungsträger zurückgeführt werden, induziert durch die Phasenseparation. Ein Vergleich von DCV2-5T-Molekülen mit Methyl- und Butyl-Seitenketten führt zu ähnlichen Resultaten: Solarzellen mit DCV2-5T substituiert mit Methyl- Seitenketten sind effizienter als die der butyl-substituierten Moleküle. Dies korreliert wiederum mit einer signifikant erhöhten Lebensdauer der Ladungsträger in Mischschichten der methyl-substituierten Verbindung.

The synthesis of benzo[e]dimethyldihydropyrene (BDHP) photoswitches with ter-27, quarter-36, and quinque-28 thiophene oligomers attached on the same side of the switch was achieved using Stille coupling reactions. BDHP photoswitches with bi-75, ter-76 and quinque-77 thiophene oligomers attached directly to the switch on one side, and via a carbonyl spacer on the opposite side of the switch were also synthesized. Dimethyldihydropyrene (DHP) photoswitches with a naphthoyl functional group in the 2 position were synthesized using a Friedel Crafts reaction, and ter-96, quinque-97 and septi-98 thiophene oligomers were attached on opposite sides of the switch using Stille coupling reactions. All compounds were characterized by NMR, IR UV-vis spectroscopy and mass spectrometry. The relative rates of the photo-opening reactions under excess light conditions and the UV closing reactions versus BDHP were measured. Improvements in the photo-opening properties of the oligothiophene functionalized switches compared to BDHP were observed. The most dramatic photo-opening improvement was found for the quinquethienyl substituted DHP switch 97 which photo-opened when irradiated with visible light over 100 times faster than BDHP. UV closing rates were virtually the same as that of BDHP. However the addition of oligothiophenes led to an increase in the thermal closing reaction rates. Compounds with the naphthoyl functional group in the 2 position of DHP were found to have dramatically increased thermal closing rates. The electrochemical properties of oligothiophene functionalized BDHP and naphthoyl functionalized DHP switches in the closed form were studied by cyclic voltammetry and spectroelectrochemistry. During the oxidation cycle, a closing reaction from the cyclophanediene (CPD) form to the DHP form of the switches occurred which prevented the study of the electrochemical properties of the switches in the open form. Conductivity testing was performed on the quinquethienyl substituted DHP switch 97 using a gold interdigitated micro electrode array. The conductivity of undoped 97 was greater in the closed DHP isomer than in the open CPD isomer. Irradiation with red or blue light allowed for repetitive switching between the more highly conducting closed form and the less conducting open form. When electrochemically doped, 97 showed improved conductivity over the undoped form but only the conductivity of the closed doped form could be measured due to electrochemically induced closing.