<p>Processes where a molecule absorbs visible light and then disposes of the excess energy via electron/energy transfer reactions have an important role both in nature (e.g. in photosynthesis) and in many technical applications (e.g. in photography and photovoltaics). This thesis uses different spectroscopical techniques, mainly ultrafast transient absorption, to study such processes. The thesis can roughly be divided into three parts.</p><p>In the first part, donor-acceptor systems linked by different conjugated bridges are studied. The objective was to see to what extent the conjugated link could enhance excited state energy or electron transfer, via so-called superexchange processes. The studied links do enhance the electron/energy transfer but in the electron transfer study the resulting charge separated state was very short lived.</p><p>The second part explores the possibility of constructing acceptor-donor-acceptor triads where the direction of electron transfer is determined by the electronic state of the donor. Direct evidence of electron transfer in the form of radical absorption was found from both the first and the second excited states of the donor.</p><p>In the last part, two common chromophores were investigated by transient absorption anisotropy. In the case of Ru(bpy)₃²⁺, it was found that the complex lost all memory of the polarization of the exciting light much faster than what was previously thought. This means that electron transfer between ligands is normally not the rate limiting step in electron transfer reactions involving this complex. In the case of zinc porphyrin, it was seen that the measured anisotropy differed depending on which electronic state was excited suggesting differences in the degree of coherence.</p>

This thesis describes an interdisciplinary project, where the aim is to mimic the initial reactions in photosynthesis. In photosynthesis, the absorption of light is followed by the formation of charge-separated states. The energy stored in these charge-separated states is further used for the oxidation of water and reduction of carbon dioxide. In this thesis the photo-induced processes in a range of supramolecular complexes have been investigated with time resolved spectroscopic techniques. The complexes studied consist of three types of units; photosensitizers (P) capable of absorbing light, electron acceptors (A) that are easily reduced and electron donors (D) that are easily oxidised. Our results are important for the future design of artificial photosystems, where the goal is to produce hydrogen from light and water. Two molecular triads with a D-P-A architecture are presented. In the first one, a photo-induced charge-separated state was formed in an unusually high yield (φ&gt;90%). In the second triad, photo-irradiation led to the formation of an extremely long-lived charge-separated state (τ = 500 ms at 140K). This is also the first synthetically made triad containing a dinuclear manganese unit as electron donor. Further, two sets of P-A dyads are presented. In both, the expected photo-induced reduction of the electron acceptor is diminished due to competing energy transfer to the triplet state of the acceptor. Finally, a P-P-A complex containing two separate photosensitizers is described. The idea is to produce high-energy charge-separated states by using the energy from two photons.

Processes where a molecule absorbs visible light and then disposes of the excess energy via electron/energy transfer reactions have an important role both in nature (e.g. in photosynthesis) and in many technical applications (e.g. in photography and photovoltaics). This thesis uses different spectroscopical techniques, mainly ultrafast transient absorption, to study such processes. The thesis can roughly be divided into three parts. In the first part, donor-acceptor systems linked by different conjugated bridges are studied. The objective was to see to what extent the conjugated link could enhance excited state energy or electron transfer, via so-called superexchange processes. The studied links do enhance the electron/energy transfer but in the electron transfer study the resulting charge separated state was very short lived. The second part explores the possibility of constructing acceptor-donor-acceptor triads where the direction of electron transfer is determined by the electronic state of the donor. Direct evidence of electron transfer in the form of radical absorption was found from both the first and the second excited states of the donor. In the last part, two common chromophores were investigated by transient absorption anisotropy. In the case of Ru(bpy)32+, it was found that the complex lost all memory of the polarization of the exciting light much faster than what was previously thought. This means that electron transfer between ligands is normally not the rate limiting step in electron transfer reactions involving this complex. In the case of zinc porphyrin, it was seen that the measured anisotropy differed depending on which electronic state was excited suggesting differences in the degree of coherence.

Photoinduced electron transfer is involved in a number of photochemical and photobiological processes. One example of this is photosynthesis, where the absorption of sunlight leads to the formation of charge-separated states by electron transfer. The redox equivalents built up by successive photoabsorption and electron transfer is further used for the oxidation of water and reduction of carbon dioxide to sugars. The work presented in this thesis is part of an interdisciplinary effort aiming at a functional mimic of photosynthesis. The goal of this project is to utilize sunlight to produce renewable fuels from sun and water. Specifically, this thesis concerns photoinduced electron transfer in donor(D)-photosensitizer(P)-acceptor(A) systems, in mimic of the primary events of photosynthesis. The absorption of a photon typically leads to transfer of a single electron, i.e., charge separation to produce a single electron-hole pair. This fundamental process was studied in several molecular systems. The purpose of these studies was optimization of single electron transfer as to obtain charge separation in high yields, with minimum losses to competing photoreactions such as energy transfer.Also, the lifetime of the charge separated state and the confinement of the electron and hole in three-dimensional space are important in practical applications. This led us to explore molecular motifs for linear arrays based on Ru(II)bis-tridentate and Ru(II)tris-bidentate complexes. The target multi-electron catalytic reactions of water-splitting and fuel production require a build-up of redox equivalents upon successive photoexcitation and electron transfer events. The possibilities and challenges associated with such processes in molecular systems were investigated. One of the studied systems was shown to accumulate two electrons and two holes upon two successive excitations, without sacrificial redox agents and with minimum yield losses. From these studies, we have gained better understanding of the obstacles associated with step-wise photoaccumulation of charge and how to overcome them.

No description available.

Under the electric dipole approximation, second harmonic of the incident light is scattered by a collection of randomly oriented molecular dipoles in solution due to instantaneous orientational fluctuation which is directional. If two such dipoles are correlated in space through intermolecular or other interactions, the intensity of the second harmonic scattered light (SHSL) will be related to the extent of such interactions. If two dipoles are arranged in a particular geometry by design, the geometry will determine the intensity of the SHSL. If a molecule has no dipole moment, the intensity of the SHSL will be less and is only allowed by higher order electric multipoles. If two such zero-dipole molecules interact with each other and transfer some amount of electronic charge from one to the other, the induced dipole moment will give rise to an enhanced SHSL. However, along with the direction of the dipole moment from the donor to the acceptor, the actual geometry of such molecular dimer/complex should also play an important role to determine the nature of the SHSL response. If all the isotropic nonzero components of first hyperpolarizability (β) are taken into account, from the measurement of β and related quantities such as depolarization ratios, in solution it should be possible to derive information about the geometry of the dimer/complex. This is precisely the motivation behind this thesis. Chapter 1 gives a brief introduction of 1:1 charge transfer (CT) complexes between a donor and an acceptor and their importance in chemistry. It also contains an introduction to nonlinear optics, various spectroscopic techniques to characterize CT complexes, etc. The motivation of extracting the geometry of such complexes from hyper-Rayleigh scattering (HRS) measurements in solution is presented in this chapter. In Chapter 2, all the experimental details of the unpolarized and polarization resolved HRS measurements at various excitation wavelengths have been described. Generation of infrared wavelengths (1543 nm and 1907 nm) using stimulated Raman scattering in gases have also been discussed. In Chapter 3, the first hyperpolarizability (βHRS) for two series of 1:1 molecular complexes between methyl substituted benzene donors with tetrachloro-p-benzoquinone (CHL) and dicyanodichloro-p-benzoquinone (DDQ) acceptors in solution at 1543 nm have been presented. Enhancement of βHRS due to charge transfer from the donor to the acceptor molecule which was predicted theoretically has been verified. Using linearly (electric field vector along X direction) and circularly polarized incident light, respectively, two macroscopic depolarization ratios D = I2ω,X,X/I2ω,Z,X and D' = I2ω,X,C/I2ω,Z,C in the laboratory fixed XYZ frame by detecting the SHSL in a polarization resolved fashion have been measured. The experimentally obtained first hyperpolarizability (βHRS), D and D' values, are then matched with the theoretically calculated values from single and double configuration interaction calculations using the Zerner’s intermediate neglect of differential overlap and the self-consistent reaction field (ZINDO–SDCI– SCRF) approach by adjusting the geometrical parameters. It has been found that in most of the CT complexes studied here, there exists a significant twist in the equilibrium geometry at room temperature which is not a simple slipped parallel geometry as was believed. In chapter 4, the βHRS, D and D' values of 1:1 pyridine (PY)-chloranil (CHL) complex at 1064 nm have been described. Previous theoretical studies have shown that there is a tilt angle of 77.9 degree in the gas phase PY-CHL complex. In this chapter, this prediction about the geometry of 1:1 PY-CHL complex has been probed. The experimentally found βHRS, D and D' are matched well with theoretically calculated values, using ZINDO–SDCI–SCRF, for a cofacial geometry of PY-CHL complex in solution indicating that the solution geometry is different from the gas phase geometry. In Chapter 5, the βHRS, D and D' for a series of 1:1 complexes of tropyliumtetrafluoroborate and methyl-substituted benzenes in solution at 1064 nm have been reported. The measured D and D' values vary from 1.36 to 1.46 and 1.62 to 1.72, respectively and are much lower than the values expected from a typical sandwich or a T-shaped geometry. The lowering in D and D' indicates that these complexes have higher symmetry than C2v. The value of D close to 1.5 indicates there is a significant octupolar contribution in such complexes. In order to probe it further, βHRS, D and D' were computed using the ZINDO-SDCI-SCRF technique in the presence of BF4-anion. By arranging the three BF4-ions in a C3 symmetry around the complex in such a way that electrical neutrality is maintained, the computed values are brought to agreement with experiments. This unprecedented influence of the anion on the HRS, D and D' values of these complexes are discussed in this chapter. In Chapter 6, the effect of dipolar interactions, within a multichromophoric system, on the second order nonlinear optical properties have been studied. It has been found that the βHRS response of the multichromophoric system is always larger than expected for uncorrelated chromophores demonstrating that the dipole moment of individual chromophores are not merely additive within the multichromophoric system but contribute cooperatively to the SHSL signal. Also the relative orientation and nature of the chromophores and the angle of interaction between them alter the HRS values. Chapter 7 is the concluding chapter in which all the work done in the thesis has been summarized and future direction has been proposed.

Donor-acceptor (D-A) copolymers have revolutionized the field of organic electronics over the last decade. Comprised of a electron rich and an electron deficient molecular unit, these copolymers facilitate the systematic modification of the material's optoelectronic properties. The ability to tune the optical band gap and to optimize the molecular frontier orbitals as well as the manifold of structural sites that enable chemical modifications has created a tremendous variety of copolymer structures. Today, these materials reach or even exceed the performance of amorphous inorganic semiconductors. Most impressively, the charge carrier mobility of D-A copolymers has been pushed to the technologically important value of 10 cm^{2}V^{-1}s^{-1}. Furthermore, owed to their enormous variability they are the material of choice for the donor component in organic solar cells, which have recently surpassed the efficiency threshold of 10%. Because of the great number of available D-A copolymers and due to their fast chemical evolution, there is a significant lack of understanding of the fundamental physical properties of these materials. Furthermore, the complex chemical and electronic structure of D-A copolymers in combination with their semi-crystalline morphology impede a straightforward identification of the microscopic origin of their superior performance. In this thesis, two aspects of prototype D-A copolymers were analysed. These are the investigation of electron transport in several copolymers and the application of low band gap copolymers as acceptor component in organic solar cells. In the first part, the investigation of a series of chemically modified fluorene-based copolymers is presented. The charge carrier mobility varies strongly between the different derivatives, although only moderate structural changes on the copolymers structure were made. Furthermore, rather unusual photocurrent transients were observed for one of the copolymers. Numerical simulations of the experimental results reveal that this behavior arises from a severe trapping of electrons in an exponential distribution of trap states. Based on the comparison of simulation and experiment, the general impact of charge carrier trapping on the shape of photo-CELIV and time-of-flight transients is discussed. In addition, the high performance naphthalenediimide (NDI)-based copolymer P(NDI2OD-T2) was characterized. It is shown that the copolymer posses one of the highest electron mobilities reported so far, which makes it attractive to be used as the electron accepting component in organic photovoltaic cells.par Solar cells were prepared from two NDI-containing copolymers, blended with the hole transporting polymer P3HT. I demonstrate that the use of appropriate, high boiling point solvents can significantly increase the power conversion efficiency of these devices. Spectroscopic studies reveal that the pre-aggregation of the copolymers is suppressed in these solvents, which has a strong impact on the blend morphology. Finally, a systematic study of P3HT:P(NDI2OD-T2) blends is presented, which quantifies the processes that limit the efficiency of devices. The major loss channel for excited states was determined by transient and steady state spectroscopic investigations: the majority of initially generated electron-hole pairs is annihilated by an ultrafast geminate recombination process. Furthermore, exciton self-trapping in P(NDI2OD-T2) domains account for an additional reduction of the efficiency. The correlation of the photocurrent to microscopic morphology parameters was used to disclose the factors that limit the charge generation efficiency. Our results suggest that the orientation of the donor and acceptor crystallites relative to each other represents the main factor that determines the free charge carrier yield in this material system. This provides an explanation for the overall low efficiencies that are generally observed in all-polymer solar cells. / Donator-Akzeptor (D-A) Copolymere haben das Feld der organischen Elektronik revolutioniert. Bestehend aus einer elektronen-reichen und einer elektronen-armen molekularen Einheit,ermöglichen diese Polymere die systematische Anpassung ihrer optischen und elektronischen Eigenschaften. Zu diesen zählen insbesondere die optische Bandlücke und die Lage der Energiezustände. Dabei lassen sie sich sehr vielseitig chemisch modifizieren, was zu einer imensen Anzahl an unterschiedlichen Polymerstrukturen geführt hat. Dies hat entscheidend dazu beigetragen, dass D-A-Copolymere heute in Bezug auf ihren Ladungstransport die Effizienz von anorganischen Halbleitern erreichen oder bereits übetreffen. Des Weiteren lassen sich diese Materialien auch hervorragend in Organischen Solarzellen verwenden, welche jüngst eine Effizienz von über 10% überschritten haben. Als Folge der beträchtlichen Anzahl an unterschiedlichen D-A-Copolymeren konnte das physikalische Verständnis ihrer Eigenschaften bisher nicht mit dieser rasanten Entwicklung Schritt halten. Dies liegt nicht zuletzt an der komplexen chemischen und mikroskopischen Struktur im Film, in welchem die Polymere in einem teil-kristallinen Zustand vorliegen. Um ein besseres Verständnis der grundlegenden Funktionsweise zu erlangen, habe ich in meiner Arbeit sowohl den Ladungstransport als auch die photovoltaischen Eigenschaften einer Reihe von prototypischen, elektronen-transportierenden D-A Copolymeren beleuchtet. Im ersten Teil wurden Copolymere mit geringfügigen chemischen Variationen untersucht. Diese Variationen führen zu einer starken Änderung des Ladungstransportverhaltens. Besonders auffällig waren hier die Ergebnisse eines Polymers, welches sehr ungewöhnliche transiente Strom-Charakteristiken zeigte. Die nähere Untersuchung ergab, dass in diesem Material elektrisch aktive Fallenzustände existieren. Dieser Effekt wurde dann benutzt um den Einfluss solcher Fallen auf transiente Messung im Allgemeinen zu beschreiben. Zusätzlich wurde der Elektronentransport in einem neuartigen Copolymer untersucht, welche die bis dato größte gemesse Elektronenmobilität für konjugierte Polymere zeigte. Darauf basierend wurde versucht, die neuartigen Copolymere als Akzeptoren in Organischen Solarzellen zu implementieren. Die Optimierung dieser Zellen erwies sich jedoch als schwierig, konnte aber erreicht werden, indem die Lösungseigenschaften der Copolymere untersucht und systematisch gesteuert wurden. Im Weiteren werden umfangreiche Untersuchungen zu den relevanten Verlustprozessen gezeigt. Besonders hervorzuheben ist hier die Beobachtung, dass hohe Effizienzen nur bei einer coplanaren Packung der Donator/Akzeptor-Kristalle erreicht werden können. Diese Struktureigenschaft wird hier zum ersten Mal beschrieben und stellt einen wichtigen Erkenntnisgewinn zum Verständnis von Polymersolarzellen dar.

Carbo- and heterocyclic compounds are of great interest to chemists. Intramolecular cyclization strategies of donor-acceptor (D-A) cyclopropanes and alkylidene malonate monoamides have excellent potential for synthesis as they offer easy access to structurally-diverse compounds. The work described in this thesis accesses the scope of the In(OTf)3-catalyzed cyclization reaction of cyclopropanes and alkylidene malonate monoamides. In(OTf)3-catalyzed reactions of alkenyl and heteroaryl cyclopropyl ketones were examined in the synthesis of functionalized cyclohexenone-based derivatives (Chapter 2). Subsequent efforts to utilize a tandem cyclopropane ring-opening/Friedel-Crafts alkylation sequence of methyl 1-(1H-indolecarbonyl)-1-cyclopropanecarboxylates to prepare functionalized hydropyrido[1,2-a]indole-6(7H)-ones is discussed in Chapter 3. The extension of this tandem protocol towards the total synthesis of (±)-deethyleburnamonine is the subject of Chapter 6. Intramolecular Friedel-Crafts alkylation of N-indolyl alkylidene malonate monoamides was also examined. An In(OTf)3-catalyzed cyclization of substituted methyl 2-(1H-indole-1-carbonyl) acrylates afforded a series of 1H-pyrrolo[1,2-a]indole-3(2H)-ones (Chapter 4), whereas substrates with the indole 2-position blocked provided access to substituted 4H-pyrrolo[3,2,1-ij]quinolin-4-ones (Chapter 5).

Cette thèse porte sur l'étude de nouvelles molécules organiques par différentes méthodes de spectroscopie. La combinaison de techniques de fluorescence résolue en temps, d'absorption différentielle résolue en temps et de spectro-électro-chimie avec des méthodes d'analyse globale permet de déterminer la photo-dynamique des molécules étudiées.Deux familles de molécules ont été étudiées. La première est une antenne de type donneur basée sur le pigment BODIPY. La seconde consiste en une triade donneur-accepteur-donneur (DAD) ayant des propriétés d'auto-organisation. Après une première génération de mol écules dont on a montré les limitations (temps de vie de l'état transfert de charge très court, d'environ 55 ps), une seconde génération de mol écules a été développée, incluant de nombreuses variations du groupe donneur, ce qui a permis de déterminer l'impact des-dites variations. Entre autres, un temps de vie de l'état transfert de charge de plus d'une nanoseconde est observé. / The topic of this thesis is the study -through different spectroscopy methods- of new organic molecules for photovoltaic applications. Combination of time resolved fuorescence, time resolved differential absorption and spectro-electro-chemistry with global analysis methods allowed to determine the photo-dynamics of the studied molecules. Two familiesof molecules have been studied. The first one is a donor-type antenna based on the BODIPY dye. The second consists in a donor-acceptor-donor (DAD) triad, with self-organizing properties. After a first generation of molecules that we proved to be limited by a short life time of its charge transfer state (about 55 ps), a second generation of molecules wasdeveloped, including several variation of the donor group, which allowed to study the impact of said variation. Among others, a charge transfer state lifetime longer than 1 nanosecond was observed.

Les matières premières biosourcées s'avèrent être une possibilité de substitution du pétrole de plus en plus prisée dans le domaine des matériaux. De plus, l'utilisation de procédé propre limitant l'impact environnemental du développement de matériau est aujourd'hui incontournable. Dans ce contexte, l'acide aminé L-lysine, un nouveau synthon issu des biotechnologies blanches peu étudié dans le domaine de la chimie des matériaux, a été retenu. Ce synthon sera modifié pour la conception de macromonomères polymérisables sous irradiation UV. En effet, la technique de photopolymérisation est un procédé propre en plein essor, et qui permet le développement de revêtement.La L-lysine étant peu soluble dans les milieux organiques classiques, une étape de transformation est nécessaire pour améliorer sa processabilité. Ainsi, la polycondensation en masse de la L-lysine a conduit à des oligomères de poly-L-lysine de faibles masses molaires. La détermination de la structure obtenue a été réalisée par différentes techniques d'analyses. Ces oligomères sont alors greffés par des fonctions photopolymérisables dans des conditions douces. Le choix s'est porté sur des fonctions accepteur et donneur d'électron. Enfin, l'étude de la photopolymérisation des oligomères de L-lysine greffés accepteurs donneurs a été effectuée par la technique UV aqueuse, une technique innovante et respectueuse de l'environnement, dans différentes conditions pour en optimiser le système. / Biobased raw materials are an interesting and promising option for the substitution of fossil resources in material design. Moreover, using green processes which limit environmental impact of the material conception can't be avoided nowadays. In this context, the L-lysine amino acid, a building block made by white biotechnologies and poorly described in material field has been evaluated. As photopolymerization is a green process in great expansion and allowing coating design, this building block has been modified into a photocurable macromonomer.L-lysine is hardly soluble in usual organic solvents, a transformation step is necessary in order to improve its processability. Thus, L-lysine polycondensation has been tackled and led to oligomers of poly-L-lysine with low molar mass and improved solubility. In addition, the structure determination has been undertaken by different analytic technics. These oligomers can thus be grafted with photocurable functional groups in mild conditions. The chosen photocurable functional groups are donor acceptor of electron. At last, the photopolymerization of L-lysine based oligomers grafted with donor acceptor functional groups has been done by UV waterborne technic which is innovative and environmentally friendly. The photopolymerization has been carried out in different conditions in order to optimize the process.