Les techniques de spectroscopie femtoseconde permettent d’étudier les processus de conversion d’énergie dans les système organiques. Elles permettent d’étudier les populations photo-générées et leur évolution à l’échelle de ces photoréactions. Elles permettent de comprendre les transferts d’énergie et de charge intra- et inter-moléculaires à l’origine du fonctionnement de ces systèmes.La protéine de rétinal Anabaena sensroy Rhodopsin est un photocommutateur naturel, qui est étudié afin de comprendre les paramètres à l’origine de l’efficacité quantique d’isomérisation. Nous avons pu déterminer cette efficacité quantique pour les deux formes stables du rétinal ainsi que leur dynamique d’isomérisation dans les mêmes conditions expérimentales.La génération de charge dans des couches actives pour le photovoltaique organique est étudiée dans un système composé d’un mélange de PCBM et d’un donneur organique dérivé du colorant BODIPY. L’influence de la nanostructuration de la couche active sur la génération de charge est étudiée. La génération de charge est limitée dans ce système par la recombinaison des charges générées et par la diffusion des excition aux interfaces donneur-accepteur. Ces observations indiquent que l’amélioration de la nanostructuration de la couche active peut permettre d’augmenter les rendements de photo-génération de charge. / Femtosecond transient spectroscopies are used to investigate photonic energy conversion inorganic systems. These techniques allow to observe the ground and excited states of themolecules at the timescale of the photoreactions. It is used to understand the inter- andintramolecular energy and charge transfers leading to the desired photochemical process.The natural photoswiching retinal protein Anabaena sensory Rhodopsin is studied to understand the key parameters ruling the isomerisation quantum yield. We could determine the isomerisation quantum yield of both stable forms and their dynamics in the very same experimental conditions.Charge generation is investigated in small molecule bulk heterojunction active layers for organic solar cells made of PCBM and a BODIPY dye-derivative donor. The influence of the active layer morphology on charge generation is studied. The charge generation is limited by charge recombination but also by exciton diffusion to the donor-acceptor interface. The active layer morphology has to be improved to achieve more efficient organic solar cells with these materials.

This thesis describes the development of several spectroscopic methods based on impulsive vibrational spectroscopy as well as of the technique itself. The first chapter describes the ultrafast time domain Raman spectrometer including the development of two noncollinear optical parametric amplifiers for sub-10 fs pulse generation with 343 or 515 nm pumping. In the first spectroscopic study we demonstrate, for the first time, that impulsive vibrational spectroscopy can be used for recording transient Raman spectra of molecules in excited electronic states. We obtain spectra of beta-carotene with comparable, or better, quality than established frequency domain based nonlinear Raman techniques. The following two chapters address the questions on the fate of vibrational coherences when generated on a reactive potential energy surface. We photoexcite bacteriorhodopsin and observe anharmonic coupling mediated vibrational coherence transfer to initially silent vibrational modes. Additionally, we are able to correlate the vibrational coherence activation with the efficiency of the isomerisation reaction in bR. Upon generation of vibrational coherence in the second excited electronic state of beta-carotene, by excitation from the ground electronic state, we are able to follow the wavepacket motion out of the Franck-Condon region. We observe vibrationally coherent internal conversion, through a conical intersection, into the first excited electronic state and are hence able to demonstrate that electronic surface crossings can occur in a vibrationally coherent fashion. Additionally, we find strong evidence for vibronic coupling mediated back and forth crossing between the two electronic states. As a combination of this work we develop a IVS based technique that allows for the direct recording of background and baseline free Raman spectra in the time domain. Several proof of principle experiments highlight the capabilities of this technique for time resolved Raman spectroscopy. In the final chapter we present work on weak-field coherent control. Here, we address the question of whether a photochemical reaction can be controlled by the phase term of an electric excitation field, in the one photon excitation limit. We study the systems rhodamine 101, bacteriorhodopsin, rhodopsin and isorhodopsin and, contrary to previous reports, find no evidence for one photon control.

La nature utilise des réactions de transfert de charge (TdC) dans de nombreuses fonctions biologiquesfaisant intervenir des cofacteurs à activité redox, comme les flavines (FAD et FMN). Le TdC dans les protéines s’effectue souvent par la formation d'intermédiaires radicalaires. Les acides aminés tyrosine(TyrOH) et tryptophane sont impliqués comme intermédiaires majeurs. Les radicaux tryptophanyle ont été caractérisés auparavant dans leurs formes protoné et déprotoné. Cependant, les radicaux tyrosyles n'ont été caractérisés que dans la forme neutre et on pensait qu'ils étaient formés par extraction électronique et déprotonation. Les intermédiaires à courte durée de vie sont souvent difficiles à observer dans les réactions biochimiques, mais peuvent être peuplés s'ils sont formés photochimiquement par de courtes impulsions.Nous avons caractérisé des intermédiaires dans des réactions non-fonctionnelles de TdC dans des flavoprotéines en utilisant la spectroscopie femtoseconde de fluorescence et d'absorption. Des états excités et produits formés dans le type sauvage et des formes mutantes de la flavo-enzyme méthyltransférase TrmFO de Thermus thermophilus ont été étudiés. Dans le site actif de cette enzyme, une tyrosine (Tyr343) est empilée sur le cycle isoalloxazine de la FAD, et une cystéine (Cys51) peut former un adduit avec la FAD très fluorescente. Dans le mutant C51A, la fluorescence du FADox est fortement quenchée par transfert d'électrons de la Tyr343 dans ~1 ps. L'état produit résultant présente une caractéristique spectrale distincte avec une forte bande d'absorption à ~490 nm, encore jamais associée à aucune espèce radicalaire, qui a été attribuée pour la première fois au cation radical de la Tyr343 (TyrOH•+). L’état FAD•-TyrOH•+, est de très courte durée car il retombe par recombinaison de charge en ~3 ps.. Cette étude démontre que- malgré le très bas pKa de TyrOH•+ -le transfert d’électrons à partir de la tyrosine peut avoir lieu sans transfert concomitant de proton.De plus, des expériences de photosélection par polarisation ont permi d’estimer, l’orientation du moment dipolaire de la nouvelle transition entre FADox et TyrOH•+ dans le TrmFO C51A à 31°±5°. Ce résultat évalue l'orientation du moment dipolaire au sein du cycle phénolique. La découverte de directions distinctes pour la bande de transition de la flavine excitée et la transition à 490 nm confirme leur origine dans différentes entités moléculaires.Sur la base des résultats de TrmFO, nous avons réexaminé la photochimie de la flavoprotéine modèle glucose oxydase (GOX). Ddes résidus de tryptophane et de tyrosine sont situés proche du FAD et l'évolution du photoproduit à l'échelle picosecondes est plus complexe. Des phases de déclin de l'état excité avec des constantes de temps de 1 et ~4 ps ont été observées, ainsi que des phases pour l'évolution de l'état produit de ~4 ps, ~37 ps et une phase plus longue. Un modèle complet de la séparation et de recombinaison des charges dans GOX impliquant, des radicaux de tyrosine et de tryptophane, ainsi que des différents états redox du FAD a été décrit. Les résultats pour les phases de 4 ps et de 37 ps mettent en évidence l’implication du radical TyrOH•+, avec des caractéristiques semblables au C51A TrmFO. Ce résultat explique des caractéristiques énigmatiques connues et indique l'implication de TyrOH•+ dans divers systèmes protéiques.A ce jour, seul le radical tyrosyle déprotoné TyrO• a été identifié comme intermédiaire fonctionnel dans plusieurs systèmes. La visualisation d'un radical TyrOH•+ dans TrmFO C51A et GOX suggère sa formation intermédiaire en tant que précurseur de TyrO• dans des réactions biochimiques fonctionnelles.Enfin, dans TrmFO, la construction de variantes spécifiques par mutagénèse dirigée a été initiée pour étudier la flexibilité du site actif en utilisant la vitesse de TdC comme marqueur conformationnel. D'autres travaux sont nécessaires pour poursuivre cette voie. / Nature employs charge transfer reactions in many biological functions. Redox-active cofactors like flavins (FAD and FMN) are often implicated in such reactions. Charge transfer in proteins often proceeds via formation of radical intermediates. The amino acid radicals of tyrosine (TyrOH) and tryptophan are thought to play important roles as intermediates in intra- and interprotein charge transfer reactions. Tryptophanyl radicals (both protonated cation and deprotonated neutral forms), had been characterized before. However, tyrosyl radicals had only been characterized in the neutral form, and were thought to be formed by concerted electron extraction and deprotonation of tyrosine. Short-lived intermediates are often difficult to observe in biochemical reactions, but may be populated when they can be photochemically formed using short light pulses.In this work, we have characterized intermediates in non-functional charge transfer reactions in flavoproteins using femtosecond time-resolved fluorescence and absorption spectroscopy. Excited states and product states formed in the wild type and mutant forms of the methyltransferase flavoenzyme TrmFO from Thermus thermophilus were investigated. In the TrmFO active site, a tyrosine (Tyr343), is closely stacked on the FAD isoalloxazine ring and a cysteine (Cys51) can form a highly fluorescent adduct with the FAD. In the mutant C51A, FADox fluorescence is strongly quenched by electron transfer from the Tyr343 in ~1ps. The resulting product state displayed a distinct spectral feature- a strong absorption band at ~490 nm unlike any previously characterized radical species. It was assigned to the radical cation of tyrosine (TyrOH•+) which had never been observed before. The FAD•-TyrOH•+ intermediate, is very short-lived as it decays in ~3ps, through charge recombination. As a general conclusion, despite the very low pKa of TyrOH•+, electron transfer from tyrosine can occur without concomitant proton transfer.Using polarization photoselection experiments, we estimated the dipole moment direction for this new transition. The resultant angle between the excited FADox transition and the probed TyrOH•+ transition in C51A TrmFO was 31º±5º. This result sets the orientation of the dipole moment of the transition in the molecular frame of the phenol ring. The finding of distinct directions for the excited FAD transition band and the 490 nm transition confirms their origin in different molecular entities.Following the results from TrmFO, we reinvestigated the photochemistry in the model flavoprotein glucose oxidase (GOX). Here, both tryptophan and tyrosine residues are located in the vicinity of FAD and the photoproduct evolution on the picosecond timescale is more complex. Distinct phases of excited state decay with time constants of 1ps and ~4ps were observed, as well as phases of ~4ps, ~37 ps and a longer-lives phase for product state evolution. Consequently, a comprehensive model for the involvement of radicals of tyrosine and tryptophan and, the different FAD redox states, in the light-induced charge separation and recombination in GOX was made. Partial involvement of the TyrOH•+ radical cation, spectrally similar to C51A TrmFO, was required for the 4 ps and 37 ps phases to account for the ensemble of data. This result explains previous enigmatic features and indicates the involvement of TyrOH•+ in a variety of protein systems.So far, only the deprotonated tyrosyl radical TyrO• had been observed as a functional intermediate in several systems. The visualization of protonated TyrOH•+ radical in TrmFO C51A and GOX suggests the possibility of its intermediate formation as a precursor of TyrO• in functional biochemical reactions.Finally, in TrmFO the construction of specific variants with site-directed mutagenesis was initiated to study active-site flexibility using electron transfer rates as conformational markers. Further experimental and modeling work is required to pursue this goal.

No description available.

<p dir="ltr">Knowledge of transport processes plays a critical role in the development and application of materials in many technologies. As manufacturing technologies continue to push the geometries of materials to smaller scales, traditional means of predicting and measuring transport properties begin to fail. Micro and nanoscopic effects tend to alter transport phenomena in materials, leading to new physics and different properties from the bulk state. In particular, the dynamics of thermal transport of a material varies greatly in both spatial and temporal senses. Different energy carriers have intrinsically different mechanisms of thermal transport; depending on the time and lengths scales in question, the contribution to the overall thermal transport by one carrier may be vastly different than others. To characterize and understand the dynamics of thermal transport at these small scales, novel ultrafast experimental techniques and theories are crucially needed. This work will discuss the efforts made to develop a framework to measure and differentiate the dynamics of transport processes of a material due to different energy carriers using ultrafast optical techniques. This dissertation is organized as follows.</p><p dir="ltr">Chapter 1 gives a background in the theory of thermal transport. This will serve as the foundation for the physical models that are used to extract thermal properties from experimental works. A brief review of the advances in ultrafast experimental and theoretical works will also be given. This will assist in placing this work in the context of ongoing work in the thermal transport community. Chapter 2 illustrates the experimental setups and physical models used to measure the effective thermal transport properties of thin film materials. Steady-state optical measurements are used to quantify the effective, in-plane, anisotropic, thermal conductivity of a 2D material. Time resolved, ultrafast optical measurements are used to quantify the effective, out-of-plane, thermal conductivity of a material. Chapters 3 and 4 demonstrate the capabilities of an ultrafast spatiotemporal scanning pump-probe system, where the high temporal and nanometric resolution measurements directly probe the electron contribution to thermal transport in metals as well as the ambipolar diffusion of carriers in semiconductors. Lastly, Chapter 5 summarizes this dissertation and provides a discussion on the use of the developed experimental capabilities to probe transport of emerging materials.</p>

No description available.

No description available.

Donor-acceptor systems exhibit distinctive attributes rendering them highly promising for the emulation of natural photosynthesis and the efficient capture of solar energy. This dissertation is primarily devoted to the investigation of these unique features within diverse donor-acceptor system typologies, encompassing categories such as closely covalently linked, push-pull, supramolecular, and multi-modular donor- acceptor conjugates. The research encompasses an examination of photosynthetic analogs involving compounds such as chelated azadipyromethene (AzaBODIPY), N,N-dimethylaminophenyl (NND), phenothiazine (PTZ), triphenylamine (TPA), phenothiazine sulfone (PTZSO2), tetracyanobutadiene (TCBD), and expanded tetracyanobutadiene (exTCBD). The strategic configuration of the donor (D), acceptor (A), and spacer elements within these constructs serves to promote intramolecular charge transfer (ICT), which are crucial for efficient charge and electron transfer. The employment of cutting-edge analytical techniques, such as ultrafast transient absorption spectroscopy, is integral to the study. Furthermore, a comprehensive suite of analytical methodologies including steady-state UV-visible absorption spectroscopy, fluorescence and phosphorescence spectroscopies, electrochemical techniques (including cyclic voltammetry and differential pulse voltammetry), spectroelectrochemistry, and density functional theory calculation (DFT), collectively contribute to the comprehensive characterization of push-pull donor-acceptor systems, with a particular emphasis on their potential as highly effective solar energy harvesting application.

This thesis is concerned with the influence of nanoscale boundaries and interfaces upon the electronic processes that occur within both organic and inorganic semiconductors. Photoluminescent polymers, highly conducting polymers and nanoscale inorganic semiconductors have been investigated using state-of-the-art ultrafast optical techniques, to provide information on the sub-picosecond photoexcitation dynamics in these systems. The influence of dimensionality on the excitation transfer dynamics in a conjugated polymer blend is studied. Using time-resolved photoluminescence spectroscopy, the transfer transients both for a three-dimensional blend film, and for quasi-two-dimensional monolayers formed through intercalation of the polymer blend between the crystal planes of a SnS2 matrix have been measured. A comparison of the experimental data with a simple, dimensionality-dependent model is presented, based on point dipole electronic coupling between electronic transition moments. Within this approximation, the energy transfer dynamics are found to adopt a three-dimensional character in the solid film, and a two-dimensional nature in the monolayers present in the SnS2 -polymer nanocomposite. The time-resolved conductivity of isolated GaAs nanowires has been investigated by optical-pump terahertz-probe time-domain spectroscopy. The electronic response exhibits a pronounced surface plasmon mode that forms within 300 fs, before decaying within 10 ps as a result of charge trapping at the nanowire surface. The mobility has been extracted using the Drude model for a plasmon and is found to be remarkably high, being roughly one third of that typical for bulk GaAs at room-temperature and indicating the high quality and low bulk defect density in the nanowires studied. Finally, the time-resolved conductivity dynamics of photoexcited polymer-fullerene bulk heterojunction blends for two model polymers, P3HT and MDMO-PPV, blended with PCBM are presented. The observed terahertz-frequency conductivity is characteristic of dispersive charge transport for photoexcitation both at the π−π* absorption peak (560 nm for P3HT), and significantly below it (800 nm). The photoconductivity at 800 nm is unexpectedly high, which is attributed to the presence of a charge transfer complex. In addition, the excitation-fluence dependence of the photoconductivity is studied over more than four orders of magnitude. The time-averaged photoconductivity of the P3HT:PCBM blend is over 20 times larger than that of P3HT, indicating that long-lived positive polarons are responsible for the high photovoltaic efficiency of polymer:fullerene blends. At early times (~ ps) the linear dependence of photoconductivity upon fluence indicates that interfacial charge transfer dominates as an exciton decay pathway, generating charges with mobility of at least ~0.1cm2 V−1 s−1. At later times, a sub-linear relationship shows that carrier-carrier recombination effects influence the conductivity on a longer timescale (> 1 μs).

Inhalt der Arbeit sind Untersuchungen zu mit der Molekularstrahlepitaxie (MBE) realisierten Materialkonzepten für ultra-schnelle Anwendungen in der Photonik. Nominell undotierte und Be dotierte GaInAs/AlInAs Vielfach-Quantenfilm Strukturen (MQW) wurden auf semi-isolierenden InP Substraten bei Wachstumstemperaturen bis zu 100°C mittels MBE (LT-MBE) abgeschieden. Untersucht wurden die kristallinen, elektrischen und optischen Eigenschaften dieser Schichtstrukturen im unbehandelten und ausgeheilten Zustand. Die elektrischen und optischen Eigenschaften der LT-MQWs sind auf Zustände nahe der Leitungsbandkante von GaInAs zurückzuführen. Die Dynamik der Ladungsträgerrelaxation wurde durch Anrege- und Abtastexperimente bestimmt. Messungen der differentiellen Transmission mit zusätzlicher Dauerstrichanregung, sowie Messungen mit zwei kurz aufeinander folgenden Anregepulsen, belegen das Potential von Be dotierten unbehandelten (ausgeheilten) LT GaInAs/AlInAs MQW Strukturen für die Verwendung in optischen Schaltern mit Schaltfrequenzen in der Größenordnung von 1 Tbit/s (250 Gbit/s). Die spannungsinduzierten Änderung der Interband-Transmission von Quantenkaskadenlaser (QCL) im gepulsten Betrieb wurde anhand von 8 Band k*p Berechnungen analysiert. Die Auswirkungen unterschiedlicher Ladungsträgerverteilungen und Probenerwärmung sind gegenüber dem dominierenden Effekt des elektrischen Feldes auf die Interband Transmission zu vernachlässigen. Der Einfluss von MBE Wachstumsparameter auf die Grenzflächenqualität von AlAsSb/GaInAs Heterostrukturen wurde anhand von Hall Messungen, temperatur- und intensitätsabhängigen PL Messungen, spektralen Messungen der Interband- und Intersubbandabsorption bestimmt. Bandstruktur-Näherungsrechnungen ermöglichten, den Einfluss von In Segregation und Sb Diffusion auf die Intersubbandabsorption zu analysieren. Intersubband Übergänge bei Wellenlängen von ca. 1800 nm (1550 nm) wurden in MQW (gekoppelten QW) Strukturen realisiert. / The present work describes investigation of new material concepts accomplished using molecular-beam-epitaxy (MBE) growth for application in ultra-fast photonic components. Nominally undoped and Be doped GaInAs/AlInAs multiple-quantumwell structures (MQW) were grown by MBE at growth temperatures down to 100 °C (LT-MBE) on semi-insulating InP substrates. Crystalline, electric and optical properties of as-grown and annealed structures were investigated. Energy states near the conduction band of GaInAs determine the electrical and optical properties of LT-MQWs. The dynamics of charge carrier relaxation was studied by means of pump and probe experiments. Measurements of the differential transmission when excited by an additional cw laser and measurements utilizing two closely sequenced pump pulses support the capability of Be doped as-grown (annealed) LT GaInAs/AlInAs MQW structures for use in optical switches at switching frequencies in the 1 Tbit/s (250 Gbit/s) range. The voltage-induced change of interband transmission of InP based quantum-cascade-lasers (QCL) during pulsed mode operation was analyzed by means of 8 band k*p calculations. The impacts of varying charge carrier distributions and of electrically heated samples can be neglected compared to the dominating effect of the electrical field on the interband transmission. The impact of MBE growth parameters on the interface quality of AlAsSb/ GaInAs heterostructures were determined by means of Hall measurements, temperature- and intensity-dependent PL measurements and spectral measurements of the interband- and intersubband-absorption. The impact of In segregation and Sb diffusion on the intersubband absorption was analyzed on the basis of bandstructure calculations. Intersubband transitions at wavelengths of about 1800 nm (1550 nm) were successfully achieved in MQW (coupled QW) structures.