Die Relaxation der Styrylfarbstoffe DCM und LDS-750 nach Photoanregung in flüssiger Phase wurde mittels zeitaufgelöster optischer Spektroskopie untersucht. Dabei wurde die Breitband-Pump-Probe-Technik angewandt. Zur Charakterisierung der Relaxation von DCM im elektronischen Grundzustand wurde außerdem die Breitband-Dump-Probe-Technik (stimuliertes Emissionspumpen) eingesetzt. Für die beobachtete schnelle Relaxation von DCM wurde eine annähernd lösungsmittelunabhängige Zeitkonstante von 0.23 (( 0.04) ps im elektronisch angeregten und von 0.28 (( 0.07 ps) im elektronischen Grundzustand gefunden. Sie wurde als Konforma tionsänderung mit nur geringer Ladungsverschiebung charakterisiert. Die weitere spektrale Entwicklung wird in polarer Lösungsmittelumgebung vorwiegend von der Solvatation bestimmt. Für das ionische Polymethin LDS-750 wurden nach der Anregung solvensabhängige Kinetiken beobachtet, die sich durch die Annahme dreier möglicher Konformationen im S1 erklären lassen. / Relaxation of the stryryl dyes DCM and LDS-750 after photoexcitation in the liquid phase has been investigated by means of time-resolved optical spectroscopy. For this purpose, the broadband pump-probe technique was used. To characterize the relaxation of DCM in the electronic ground state, additionally the broadband dump-probe technique (stimulated emission pumping) was applied. An approximately solvent-independent time constant was found typical for the observed fast relaxation of DCM, with values of 0.23 ((0.04) ps in the excited and 0.28 (( 0.07 ps) in the electronic ground state. The relaxation was characterized as conformational change with only a small amount of charge transferred. The further spectral evolution in polar solvents was dominated by solvation dynamics.For the ionic polymethine species LDS-750 solvent-dependent kinetics were found after photoexcitation. They could be accounted for by assuming the existence of three different conformers within the S1 state.

Neste trabalho estudamos a forma de linha na absorção de dois fotons nas transições 4f7 de defeitos cristalinos superpostas com bandas de absorção multifonons. Escrevemos o perfil de linha sob a forma de Fano. O íon em estudo é Eu++ como defeito em um cristal de CaF2. Apresentamos o desenvolvimento da instrumentação necessária para realização do experimento, e obtemos resultados de ótima qualidade. / In this work we study the absorption of two photons in the electronic transition within the 4f 7configuration wich is superposed to the vibronic structure of 4f 7 - 4f65d transition. We describe the line shape with the Fano\'s formalism. The study was carried out on Eu+2 doped CaF2. The experimental apparatus was build and the results obtained are in good agreement with the theoretical predictions.

Neste trabalho apresentamos resultados de birrefringência opticamente induzida via absorção de um e dois fótons em filmes casting de poli (metil metacrilato) (PMMA), contendo uma nova série de compostos azoaromáticos chamados de corantes Salen, os quais podem ser usados em aplicações de memória óptica. Para a birrefringência opticamente induzida por um fóton, foi necessário um tempo de escrita maior para os compostos com metal na estrutura em comparação com o composto Salen que não contém metal, provavelmente devido a agregações do grupo azoaromático na estrutura do polímero diminuindo a mobilidade molecular. Além disso, como uma novidade em memórias ópticas deste tipo, birrefringência opticamente induzida por dois fótons pôde ser realizada nos filmes de Salen, o que pode permitir sua aplicação em memória óptica tridimensional. / In this work we present the one- and two-photon optically induced birefringence in cast films of amorphous poly(methyl methacrylate) (PMMA), containing a new series of organometallic azoaromatic compounds, referred to as Salen dyes, which may be used in optical storage applications. For the one-photon optically induced birefringence, longer writing times were required for the organometallic compounds in comparison with the nonmetal one, probably due to the higher degree of aggregation in the azoaromatic moieties that precludes molecular orientation. Furthermore, as a novelty concerning optical storage, two-photon optically induced birefringence could be achieved in the Salen dyes guest-host films, which allows their application in three-dimensional optical memories.

Dans le premier chapitre de cette thèse, nous introduisons le concept de nanodot organique (OND) comme une alternative aux quantum dots (QDs). Ces nano émetteurs «tout organique» sont préparés par synthèse bottom-up et contrôle,à l’échelle du nanoobjet, de la réponse optique par confinement du chromophore au sein d’une structure dendritique. Ceci conduit à des nanoobjets présentant une brillance exceptionnelle à un ou deux photons en faisant des composés d’intérêt majeur pour l’imagerie in vivo. Le deuxième chapitre décrit la synthèse et la caractérisation de la première famille d’OND hydrophiles. Deux types d’absorbeurs à deux photons ont été sélectionnés car présentant des propriétés optiques et des structures différentes. Ensuite, l’hydro solubilité a été assurée par l’accrochage de groupes H2N(CH2)2NEt2 à la périphérie. Dans les chapitres 3 et 4, nous proposons une alternative aux OND cationiques par greffage de chaîne polyéthylèneglycol à la périphérie. Ceci améliore la solubilité et la biocompatibilité. Un OND hydrosoluble bimodal pouvant être utilisé en IRM du19Fet imagerie de fluorescence est également préparé. Dans ce chapitre l’étude par RMN et par imagerie confocale de trois dendrimères à cœur cyclophosphazène est également décrite. Finalement, le chapitre 5 décrit la préparation de systèmes synergique agissant en tandem pour la photo libération d’un substrat «en cage». Nous avons démontré qu’en combinant une antenne collectrice avec des unités encagées,il est possible d’obtenir une libération efficace de molécules actives. Par ingénierie moléculaire nous avons préparé trois systèmes synergiques différents: (i) Une triade symétrique basée sur un chromophore portant des chaîne hydrophile TEG et connecté à unités PPG encageant une unité glutamate (ii) Une dyade comportant un chromophore et une unité PPG au sein d’une architecture phosphorée, finalement (iii) une unité dendritique portant une unité encageante et 5 absorbeurs à deux photons / In the first chapter of this dissertation, we introduce the concept of organic nanodot (OND) as an alternative to quantum dots (QDs).These purely organic nanoemitters are obtained from a rational and bottom-up route based on the control, at the single nano-object level, of the optical responses via the covalent confinement of optimized chromophores within dendrimericarchitectures. This led to tuneable nano-objects which show record one-and two-photon brightness and have been shown to be a major interest for in vivoimaging.The second chapter describes the synthesis and structural characterization of the first family of ONDwith hydrophilic properties. Two different 2P absorber modules were selected for this aim, displaying different structural and optical properties. Then, the water solubility will be ensured by linking H2N(CH2)2NEt2.at the periphery. In Chapter 3and 4we propose an alternative to the cationic ONDs by replacing the external layer, with polyethylene glycol (neutral). This synthetic approach favorsthe hydrosolubility, and the compatibility in biological environment. Awater-soluble organic nanodot-based probethat could be used for both 19F MRI and optical fluorescence imagingis alsoprepared. In the same chapter, confocal imaging and NMR studies of three types of dendrimers with a cyclotriphosphazene core are described.Finally, the aim of chapter 5is the synthesis of synergic systems acting in tandem for the photorelease of a caged substrate. We demonstrate that combining a light harvesting antenna group with uncaging subunits leads to the efficient release of active molecules. Molecular engineering allowed us to prepare three different synergic systems, (i) a symmetrical tandem triad structure, based on one chromophore bearing hydrophilic TEG chains, which is directly connected to two PPG units caging one molecule of glutamate respectively, (ii) a dyad system bearing one chromophore and one PPG in phosphorus scaffold, finally (iii) a dendritic scaffold bearing 6 available position that was coated both with one equivalent ofuncaging moietyand the remaining positions with 2P absorbing modules.

The objective of this thesis was to develop novel technologies for measuring the physical characteristics of high-speed pulse trains, for use in performance monitoring applications. This thesis describes the development of three separate techniques that perform measurements in either the time domain, frequency domain or the phase space of the optical signal. The first section investigates phase-sensitive pulse measurement techniques. A high- resolution SHG-FROG apparatus was custom-designed to measure 40GHz RZ pulse trains, from which an operational characterisation of a Mach-Zehnder modulator (MZM) was realised. A numerical model of a nonlinear pulse compressor was developed to compress 40GHz RZ pulses from 8.5ps down to 3.4ps. These pulses were time-division multiplexed to 80GHz, and phase-retrievals of the 80GHz pulse trains were measured. A comparison between the techniques of SHG-FROG and linear spectrogram has been undertaken for 10GHz pulse sources, exposing SHG-FROG's weaknesses at this particular repetition rate. The second section investigates a simple, time-averaged, nonlinear detection technique. Two-photon absorption in a GaAs/InGaAs quantum-well laser diode was used to measure the duty cycle (and by extension, the pulse duration) of a range of pulse sources. This technique was further developed to measure the extinction ratio of NRZ pulse trains. Additionally, the pulse duration of a mode-locked laser source was measured using the nonlinear absorption in a 1-m length of As2Se3 Chalcogenide glass fiber. This demonstrates that the nonlinear properties of this glass may well find application in future instrumentation. The third section investigates the development of an ultra-high resolution swept heterodyne spectrometer. This spectrometer was used to spectrally-distinguish repetitive 8-bit NRZ patterns at 2.5Gbit/s. It was also used to measure the chirp parameter of an X-cut LiNbO3 MZM, revealing a chirp parameter of απ/2 < 0.1 across a modulation band- width of 250-2500MHz. Additionally, the distinctive CW spectrum of a DFB laser diode was measured. Analysis of the measured CW spectrum yielded a linewidth enhancement factor of α≃ 1.8 and also the relative intensity noise of the DFB laser diode.

Gesunde sowie qualitativ hochwertige Nahrungsmittel sind wichtige Voraussetzungen, um einerseits die Lebensmittelsicherheit entlang der Wertschöpfungskette (Wachstum, Verarbeitung, Lagerung und Transport) und andererseits einen vorbeugenden Verbraucherschutz zu gewährleisten. Die Belastung der Nahrung mit Rückständen jeglicher Art war in letzter Zeit häufig Mittelpunkt heftiger öffentlicher Diskussionen. Zahlreiche Untersuchungen haben gezeigt, dass unter bestimmten Bedingungen durch Pilze gebildete Giftstoffe, so genannte Mykotoxine, die Ernteprodukte belasten und es bei deren Verzehr durch Menschen oder Tiere zu Vergiftungen kommen kann. Die FAO schätzt, dass etwa 25% der Weltproduktion von Nahrungsmitteln mit Mykotoxinen kontaminiert und in 20% der Getreideernte der Europäischen Union messbare Konzentrationen an Mykotoxinen detektierbar sind. Damit die Lebensmittelsicherheit weiterhin gewährleistet bleibt, werden neben den Routinemethoden schnellere und zerstörungsfreie Methoden benötigt, um die Lebensmittel direkt vor Ort auf Schimmelpilze und deren Mykotoxine zu untersuchen. In dieser Arbeit wird das Potenzial von ausgewählten optisch-basierten spektroskopischen Methoden für die in-situ bzw. in-line Detektion von Schimmelpilzen sowie Mykotoxinen in Getreide(produkten) untersucht. Es werden Absorptions- und Reflexionsmethoden einerseits und Fluoreszenztechniken andererseits eingesetzt. Die spektroskopischen Methoden werden dabei auf Proben unterschiedlicher Komplexität angewandt - beginnend mit der Untersuchung der photophysikalischen Eigenschaften der reinen Mykotoxine in Lösung über künstlich mit verschiedenen Mykotoxinen kontaminierten Getreideproben bis hin zu mit Pilzen befallenem Getreide und hochveredelte Lebensmittel (Wein und Bier) als Proben höchster Komplexität. / Problems of food safety have led to an increasing concern regarding contamination of foods and feeds with mycotoxins and the relevant toxigenic fungi, mainly Aspergillus, Penicillium and Fusarium genera. There is a real need for rapid, sensitive and inexpensive sensors for the detection of toxigenic fungi and mycotoxins, both in the field and after harvest in order to obtain real-time monitoring data on contamination and this assist in food safety assessment. This will result in an enormous cost saving to the farmers as well as to agro-food industry through the prevention and reduction of product recalls and reduced treatment costs. The German Ministry of Education and Research (BMBF) has provided funding of more than 1.9 million Euros from July 2006 to December 2009 for the large joint project "ProSeso.net2" on the development of innovative sensor-based techniques and processes in the field of food quality and safety. In this research-project "Exploration of sustainability potentials by use of sensor-based technologies and integrated assessment models in the production chain of plant related food" 13 partners from universities, non-university institutions and industry cooperate within seven subprojects. The expected results shall contribute to maintain freshness and improve safety of the food production chain. In the subproject “Indicators and sensor technology for the identification of mycotoxin producing fungi in the processing of grain” spectroscopic methods are tested for in-situ and in-line detection of moulds and/or mycotoxins. This presentation focuses on some possible spectroscopic methods for the rapid detection of mycotoxins and fungi on grains. Methods based on one- and two-photon-induced fluorescence spectroscopy are highly attractive because of their outstanding sensitivity and selectivity. In order to utilize a fluorescence technique for the analysis of the mycotoxins in food and feedstuff as well as for basic research on the fungal metabolism, the photochemistry and photophysics of the mycotoxins and fungi need to be elucidated in detail, especially the influence of solvent parameters such as polarity and pH value. Consequently, for a sensitive and selective spectroscopic analysis, it is indispensable to take the specific photophysic of the known mycotoxins into account in order to minimize serious limitations upon sensitivity, selectivity, and accuracy of a potential fluorescence-based sensing application. The spectroscopic techniques are complemented by chemometric tools (Principle Component Analysis) to extract the desired chemical information, e.g. with respect to presence of contaminations. The combination of data obtained from different spectroscopic methods (such as optimal excitation and emission wavelength, fluorescence decay times, and fluorescence quantum efficiency) on the one hand side and NIR spectroscopy on the other side shows promising results for the qualitative as well as quantitative identification of mycotoxins grains. Moreover, NIR reflectance spectra yield additional information on ingredients, moisture content, and the presence (or absence) of fungi in the sample.

Inter-molecular interactions have significant influences on linear and nonlinear optical properties of molecules including one- and two-photon absorptions, emissions, and various high order nonlinear polarizations. The related investigation has become an active and challenging research area. The theoretical structure-to-property relationship obtained from quantum chemical calculations of single organic conjugated molecules often can not be directly applied to real materials in condensed phases. One has to consider the effect of environment, that is, inter-molecular interactions, where the model systems experience in real experiments or applications. The change of molecular conformations under all kinds of interactions and its effects on linear and nonlinear optical properties are the central issue of this thesis. Special attentions have been paid to symmetrical diamino substituted distyrylbenzene chromophores with different torsional angles, two dipolar merocyanine dyes of various orientations, two isomers of a V-shaped 2-hydroxypyrimidine derivative and their various dimers, and the structural fluctuations of interacting polar chromophores in solutions. Quantum chemical methods in combination with molecular dynamics simulations have been employed to study molecular conformations and optical properties in solutions, in particular the solvent and aggregation effects on one- and two-photon absorption. More specifically, time-dependent density functional theory has been used for all electronic calculations, while the polarizable continuum model and supermolecule approach have also been employed to take into account solvent effects. Moreover, the propagation of an ultrashort laser pulse through a one-dimensional asymmetric organic molecular medium which possesses large permanent dipole moments has been simulated by solving full Maxwell-Bloch equations using predictor-corrector finite-difference time-domain method. We have focused on the supercontinuum generation of spectra and the formation of attosecond pulses. / QC20100630

Molecular photoabsorption enhancement under ambient solar radiations can improve efficiency substantially in renewable energy production. Here, we explore the theoretical basis and experimental evidences that nanostructured molecular assemblies exhibit an unprecedented property of synergistic photon absorption enhancement. The molecular mechanism of this enhancement phenomenon originates from the combined effect of the photon-molecule interaction and the electronic energy transfer between two adjacent molecular assemblies. For a natural system, the synergistic photon absorption enhancement factor of green algae (Chlorella vulgaris) in vivo at 632.8 nm was determined to be 103. This enhanced photon absorption process in nanostructured molecular assemblies opens a doorway to create entangled double excitons by incoherent solar radiations.

Structure-property relationships for two-photon absorption (2PA) in branched organic chromophores is a topic of current interest, as is the design of chromophores with advantageous properties for two-photon laser scanning microscopy (2PLSM). The main goals of this dissertation were to study and explain the one-photon absorption (1PA) and 2PA properties of cruciform chromophores based on 1,4-distyryl-2,5-bis(phenylethynyl)benzene with varying electron donor (D) and acceptor (A) groups, and to characterize the 2PLSM-relevant response of some of these chromophores and a set of dipolar chromophores to binding with zinc ions. The compounds were studied by 1PA, fluorescence and 2PA spectroscopy. A ππ* exciton model was developed to explain the spectral properties of the 1,4-distyryl-2,5-bis(phenylethynyl)benzene cruciform with no D or A groups or with four identical D groups at the termini of the linear arms of the chromophore. This model indicated that there is some coupling and mixing of the lowest excited states e of the linear arms, leading to splitting of the 1PA spectrum of the cruciform. There was little coupling or mixing of the higher excited states e′ accessed in 2PA, leading to a two-band 2PA spectrum for the chromophore, in contrast to cruciform compounds in the literature with identical conjugated arms, which have one visible 2PA band. For cruciforms with D groups on the styryl arm and A character on the terminal phenyls of the phenylethynyl arms (D/A cruciforms), the ππ* exciton model was complemented with a charge-transfer (CT) exciton model describing interactions of charge-transfer pathways between the D and A groups. This model explained the broadness of the 1PA band of D/A cruciforms as well as the two 2PA bands observed for these chromophores. The fluorescence and 2PA spectral responses to binding of Zn²⁺ ions to the D or A groups of some cruciform compounds were also assessed, to provide insight into the design of new analyte-sensing cruciforms for 2PLSM that take advantage of enhancement or reduction of D/A character upon analyte binding. It was found that canceling charge donation from the D groups in differing D/A cruciforms resulted in fluorescence and 2PA spectra nearly indistinguishable from each other, suggesting that turn-off of D groups is not an optimal modality of 2PLSM analyte sensing in cruciforms. Binding Zn²⁺ to A groups was shown to result in an increase in the D/A character of the cruciform, with fluorescence peak energies that changed depending on the location of the A group. It is suggested that the use of non-binding donors and analyte-binding A groups in differing patterns on the arms could be a valuable design motif to achieve 2PLSM sensor compounds based on this cruciform structure. The 2PA spectra of a set of dipolar Zn²⁺ sensing dyes designed for ratiometric imaging in 2PLSM were also studied. These dyes had moderate 2PA strength, with redshifts of fluorescence 2PA spectra on Zn²⁺ binding. The isosbestic point of 2PA of most chromophores was within the range of 2PLSM excitation sources commonly used, rendering these dyes good candidates for use in ratiometric sensing in 2PLSM.

Στην εργασία αυτή θα ασχοληθούμε με τη διφωτονική απορρόφηση και τις εφαρμογές της. Θα πρέπει πρώτα να πούμε δύο λόγια γι’αυτήν, να εξηγήσουμε περί τίνος πρόκειται και γι’αυτό θα αρχίσουμε από τα βασικά. Όταν ηλεκτρομαγνητική ακτινοβολία κυκλικής συχνότητας ω0 προσπίπτει σε ένα υλικό μέσο, τα άτομά του λειτουργούν σαν ταλαντωτές, με την έννοια πως ταλαντώνονται στη συχνότητα της ακτινοβολίας, απορροφώντας την και επανεκπέμποντάς την. Παρομοιάζοντας έναν τέτοιο ταλαντωτή με σύστημα μάζας-ελατηρίου, το ρόλο της μάζας τον παίζει το ηλεκτρόνιο (για λόγους απλότητας θεωρούμε πως το άτομο έχει μόνο ένα) και το ρόλο του ελατηρίου οι δυνάμεις έλξης ηλεκτρονίου-πυρήνα. Το «ελατήριο» στη μιά του άκρη είναι στερεωμένο στον πυρήνα, που λόγο μεγάλης μάζας (σε σύγκριση με το ηλεκτρόνιο) θεωρείται ακίνητος. Όταν η ένταση του Η/Μ πεδίου είναι μικρή, το ηλεκτρόνιο δεν απομακρύνεται πολύ από τη θέση ισορροπίας του και ο ταλαντωτής μας μπορεί να θεωρηθεί αρμονικός, και έχουμε γραμμικά φαινόμενα. / -