The two major topics studied in this dissertation are the gold(I) pyrazolate trimer {[Au(3-R,5-R’)Pz]3} complexes in aqueous chitosan polymer and phosphorescent polymeric nanoparticles based on platinum(II) based complex. The first topic is the synthesis, characterization and optical sensing application of gold(I) pyrazolate trimer complexes within aqueous chitosan polymer. A gold(I) pyrazolate trimer complex, {[Au(3-CH3,5-COOH)Pz]3}, shows high sensitivity and selectivity for silver ions in aqueous media, is discussed for optical sensing and solution-processed organic light emitting diodes (OLEDs) applications. Gold(I) pyrazolate trimer complexes are bright red emissive in polymeric solution and their emission color changes with respect to heavy metal ions, pH and dissolved carbon dioxide. These photophysical properties are very useful for designing the optical sensors. The phosphorescent polymeric nanoparticles are prepared with Pt-POP complex and polyacrylonitrile polymer. These particles show excellent photophysical properties and stable up to >3 years at room temperature. Such nanomaterials have potential applications in biomedical and polymeric OLEDs. The phosphorescent hybrid composites are also prepared with Pt-POP and biocompatible polymers, such as chitosan, poly-l-lysine, BSA, pnipam, and pdadmac. Photoluminescent enhancement of Pt-POP with such polymers is also involved in this study. These hybrid composites are promising materials for biomedical applications such as protein labeling and bioimaging.

The synthesis of N-heterocyclic carbene precursors based on the hexahydroimidazo[1,5-a]pyridine and their corresponding cyclometalated platinum(II) carbene complexes is reported. All compounds are fully characterized by standard techniques and additionally X-ray structures could be obtained for three complexes. The photophysical properties of these platinum complexes were investigated by absorption and photoluminescence measurements. All complexes showed strong phosphorescence at room temperature in the sky-blue area with quantum yields of up to 71 %. Additionally, their electrochemical properties were examined by voltammetry experiments. All results were rationalized by quantum chemical DFT calculations (PBE0/6-311G*).

The structural, electronic, and optical properties of a series of organic pi-conjugated polymer, oligomer, or molecular materials of interest for applications in organic electronics are described. For this purpose, quantum-chemical techniques ranging from Density Functional Theory to Hartree-Fock ab initio and semiempirical methods are used to evaluate the charge-transport, charge-transfer, and electroluminescence properties of pi-conjugated organic materials. First, the effect of electronic polarization on the charge-transport parameters of organic semiconductors is discussed. A generalized methodology based on a basis set orthogonalization procedure is developed to determine reliable charge-transport characteristics. The charge-transport parameters of a number of organic semiconductors such as oligoacenes and derivatives are studied with this methodology. Then, triplet emitters, in particular iridium complexes, that achieve high efficiency electroluminescence in organic light-emitting diodes are discussed. The effects of ligand substitution and orientation on the luminescent properties of iridium compounds are investigated in order to develop structure-properties relationships. The emission properties of these complexes are found to be governed by an interplay between metal-to-ligand charge transfer excitations and ligand-centered and/or interligand excitations. The extent of mixing of these various excitations turns out to be highly dependent on the nature of the substituents. Design strategies to shift the emission color towards deep blue are proposed. Finally, several classes of materials acting as hosts for phosphorescent emitters are studied. It is shown that restricting the conjugation length leads to high energy gap host materials suitable for blue phosphorescent emitters.

Les espèces réactives de l'oxygène sont générées dans l'environnement biologique dans le cadre du métabolisme, mais elles peuvent aussi être produites en excès dans le cas de stress oxydatif provoqué par exemple par une exposition aux rayons UV. Dans le travail présenté ici, nous sommes intéressés par l'oxydation des protéines par deux de ces espèces réactives de l'oxygène : le peroxyde d'hydrogène, oxydant plutôt faible avec un temps de vie long, et l'oxygène singulet, oxydant fort avec un temps de vie court. L'action de ce dernier sur les protéines est étudiée en utilisant la spectroscopie de phosphorescence résolue en temps et l'oxydation des protéines par le peroxyde d'hydrogène est suivie par spectroscopie Raman. Dans ce cas, un travail préliminaire a été nécessaire afin d'attribuer de manière précise les bandes Raman des chaînes latérales des résidus d'acides aminés. Pour les deux types d'oxydations, les constantes de vitesse des réactions ont été déterminées pour trois protéines modèles. La stratégie suivie est d'utiliser de petits fragments de protéines tels que des acides aminés libres et des tripeptides pour comprendre ce qui se passe à l'échelle de la protéine. Cela nous aide à souligner l'importance de l'environnement protéique. Dans le cas de l'étude par spectroscopie Raman, l'influence du nombre de liaisons peptidiques sur les spectres obtenus depuis l'acide aminé libre, au tripeptide, jusqu'à la protéine est aussi mis en évidence.

Ce travail est consacré à l'étude d'un pigment phosphorescent (luminophore), le monoaluminate de strontium dopé à l'europium et au dysprosium : SrAl₂O₄ : Eu, Dy. Il a abouti à la modélisation de la luminescence de ce composé (fluorescence & thermoluminescence (TL)), exposée à l'aide du schéma des bandes d'énergie usuellement employé pour décrire ces phénomènes (chapitre IV). Ce système s'est révélé se comporter comme une pile, stockant, sous l'effet de la lumière du jour, de l'énergie sous forme de paires électron/trou dissociées. Chaque partie, piégée par les défauts du luminophore, est libérée par activation thermique a température ambiante. Elles se recombinent ensuite libérant le surplus d'énergie sous forme d'une émission lumineuse verte (525 nm). L'explication de ces mécanismes optoélectroniques à nécessité la compréhension du rôle de chacun des composants du système : la matrice (SrAl₂O₄) et les éléments dopants (Eu & Dy) identifié séparément. La première partie de ce travail (chapitre II) à pour cela été dédiée à l'étude de la matrice et a permis de mettre au point un mode de synthèse par réaction solide/solide, sous atmosphère contrôlée, entre le carbonate de strontium et l'alumine gamma. L'influence des différents paramètres de synthèse (stœchiométrie des réactants, durée, température et atmosphère de calcination) a permis de caractériser les propriétés optoélectroniques de la matrice (Emission de fluorescence bleue a 440 nm & 3 pics de TL à - 170, -70 et 0°c). Le rôle du dysprosium, puis de l'europium et enfin leur interaction ont fait l'objet d'une étude particulière (chapitre III). L'émission verte à 525 nm a ainsi pu être attribuée à l'europium divalent (Eu²⁺), l'interaction Eu-Dy étant quant à elle responsable du phénomène de phosphorescence.

This work focusses on the high brightness performance of phosphorescent organic light-emitting diodes (OLEDs). The use of phosphorescent emitter molecules in OLEDs is essential to realize internal electron-photon conversion efficiencies of 100 %. However, due to their molecular nature, the excited triplet states have orders of magnitude longer time constants compared to their fluorescent counterparts which, in turn, strongly increases the probability of bimolecular annihilation. As a consequence, the efficiencies of phosphorescent OLEDs decline at high brightness – an effect known as efficiency roll-off, for which it has been shown to be dominated by triplet-triplet annihilation (TTA). In this work, TTA of the archetype phosphorescent emitter Ir(ppy)3 is investi- gated in time-resolved photoluminescence experiments. For the widely used mixed system CBP:Ir(ppy)3, host-guest TTA – an additional unwanted TTA channel – is experimentally observed at high excitation levels. By using matrix materials with higher triplet energies, this effect is efficiently suppressed, however further studies show that the efficiency roll-off of Ir(ppy)3 is much more pronounced than predicted by a model based on Förster-type energy transfer, which marks the intrinsic limit for TTA. These results suggest that the emitter molecules show a strong tendency to form aggregates in the mixed film as the origin for enhanced TTA. Transmission electron microscopy images of Ir(ppy)3 doped mixed films give direct proof of emitter aggregates. Based on these results, two concepts are developed that improve the high brightness performance of OLEDs. In a first approach, thin intrinsic matrix interlayers are incorporated in the emission layer leading to a one-dimensional exciton confinement that suppresses exciton migration and, consequently, TTA. The second concept reduces the efficiency roll-off by using an emitter molecule with slightly differ- ent chemical structure, i.e. Ir(ppy)2(acac). Compared to Ir(ppy)3, this emitter has a much smaller ground state dipole moment, suggesting that the improved performance is a result of weaker aggregation in the mixed film. The knowledge gained in the investigation of triplet-triplet annihilation is further used to develop a novel emission layer design for white organic LEDs. It comprises three phosphorescent emitters for blue, green, and red emission embedded in a multilayer architecture. The key feature of this concept is the matrix material used for the blue emitter FIrpic: Its triplet energy is in resonance with the FIrpic excited state energy which enables low operating voltages and high power efficiencies by reducing thermal relaxation. In order to further increase the device efficiency, the OLED architecture is optically optimized using high refractive index substrates and thick electron transport layers. These devices reach efficiencies which are on par with fluorescent tubes – the current efficiency benchmark for light sources. / Diese Arbeit richtet ihren Fokus auf die Untersuchung der Leistungsfähigkeit von phosphoreszenten, Licht-emittierenden organischen Dioden (OLEDs) im Bereich hoher Betriebshelligkeiten. Phosphoreszente Emittermoleku ̈le werden in OLEDs eingesetzt, um interne Elektron-Photon Konversionseffizienzen von 100% zu erreichen. Begründet in ihrer chemischen Struktur, weisen die angeregten Triplett-Zustände dieser Emitter um Größenordnungen längere Zeitkonstanten als die Emission fluo- reszenter Materialien auf, sodass die Wahrscheinlichkeit bimolekularer Auslöschung stark ansteigt. Dies resultiert in einem deutlichen Effizienzrückgang phosphoreszenter OLEDs bei großen Leuchtdichten. Dieser als Roll-off bekannter Effekt wird bei hohen Anregungsdichten hauptsächlich durch Triplett-Triplett Annihilation (TTA) bestimmt. In der Arbeit wird TTA an einem Modellmolekül, dem phosphoreszenten Emit- ter Ir(ppy)3, in zeitaufgelösten Photolumineszenz Experimenten untersucht. Für das bekannte Emittersystem CBP:Ir(ppy)3 wird bei hohen Anregungsdichten Host-Guest TTA beobachtet, was einen zusätzlichen, ungewünschten TTA Kanal darstellt. Dieser Effekt wird durch das Verwenden von Matrix Materialien mit höherer Triplett Energie vermieden, jedoch zeigt sich in weiteren Untersuchungen, dass der Roll-off deutlich stärker ist als von einem auf Förster Energieübertrag basierendem Modell vorhergesagt, welches selbst ein intrinsisches Limit für TTA in phosphoreszenten Systemen beschreibt. Die Diskrepanz zwischen experimenteller Beobachtung und Modellvorhersage wird durch eine starke Tendenz des Emitters, Aggregate zu bilden, erklärt, was TTA deutlich verstärkt. Diese Aggregate werden mit Hilfe von Transmissionselektronenmikroskopie an Ir(ppy)3-dotierten Mischsystemen direkt nachgewiesen. Basierend auf diesen Resultaten werden zwei Konzepte entwickelt, um die Effizienz phosphoreszenter Systeme bei hohen Helligkeiten zu verbessern. Im ersten Ansatz werden dünne intrinsische Schichten des Matrixmaterials in die Emissionsschicht eingebaut, was die Exzitonenbewegung in einer Raumrichtung und damit auch TTA stark unterdrückt. Das zweite Konzept reduziert den Effizienz Roll-off durch die Verwendung eines phosphoreszenten Emitters Ir(ppy)2(acac) mit einer leicht abgeänderten Molekularstruktur. Im Vergleich mit Ir(ppy)3 weist dieser ein deutlich kleineres Dipolmoment im molekularen Grundzustand auf, wodurch die Aggregation vermindert wird. Aufbauend auf den Ergebnissen der TTA wird ein neuartiges Emissionsschicht-Design für weißes Licht entwickelt. In diesem Konzept werden drei phosphoreszente Materialien für blaue, grüne und rote Farbe in eine Vielschicht-Architektur eingebracht. Das Hauptmerkmal der Emissionsschicht ist die Wahl des Matrix-Materials für dem blauen Emitter FIrpic: Seine Triplett Energie liegt resonant zu dem FIrpic Triplett Zustand, wodurch niedrige Betriebsspannungen und hohe Leistungseffizienzen ermöglicht werden, da die thermische Relaxierung reduziert wird. Um die Ef- fizienz dieser weißen OLEDs weiter zu erhöhen, wird die entwickelte OLED Architektur zusätzlich durch die Verwendung von hochbrechenden Substraten und dicken Elektronen-Transportschichten optisch optimiert. Bei beleuchtungsrelevanten Helligkeiten erreichen diese OLEDs das Effizienzniveau von Leuchtstoffröhren – letztere stellen heute den Effizienz-Maßstab dar.

Organic light-emitting diodes (OLEDs) have drawn much attention in the last two decades. In recent years, the power efficiency of OLEDs has been increased to exceed the efficiency of fluorescent light bulbs. However, such high-efficiency devices are typically based on small molecules that have to be evaporated in vacuum. A much higher fabrication throughput and therefore lowered costs are expected if high-efficiency OLEDs were processed from solution. This thesis shows how solution-processed electrophosphorescent multilayer OLEDs can be achieved by starting with an evaporated three-layer device structure and replacing layer by layer with a solution-processed layer. First, the hole-transport layer was replaced by a polymer and high efficiencies were observed when using a hole-transport polymer with a high ionization potential and a low hole mobility. Then, the emissive layer was replaced by a copolymer consisting of hole-transport groups and emissive complexes in its side-chains. OLEDs with four different colors are shown where the orange devices showed the highest efficiency. The orange copolymer was further optimized by making changes to the chemical nature of the polymer, such as different molecular weight, different concentrations of the emissive complex and different linkers between the side-chains and the polymer backbone. Finally, a three-layer solution-processed OLED was fabricated by crosslinking the hole-transport and the emissive layer, and by spin-coating an electron-transport polymer on top. Moreover, using the photocrosslinking properties of the emissive layer, solution-processed multilayer OLEDs of two different colors were patterned using photolithography to fabricate a white-light source with a tunable emission spectrum. Furthermore, with more and more organic semiconductors being integrated into the circuitry of commercial products, good electrical models are needed for a circuit design with predictive capabilities. Therefore, a model for the example of an organic single-layer diode is introduced in the last chapter of this thesis. The model has been implemented into SPICE and consists of an equivalent circuit that is mostly based on intrinsic material properties, which can be measured in independent experiments. The model has been tested on four different organic materials, and good agreement between model and experimental results is shown.

Doctor of Philosophy / Department of Anatomy and Physiology / David C. Poole / The components of the O2 transport pathway can be divided into (along with their respective circulations) the pulmonary, cardiovascular, and skeletal muscle systems. They must operate in tight conjunction with one another, especially during dynamic exercise, to sustain ATP production within muscle mitochondria. Any limitation placed on the O2 transport pathway will result in decreased performance. The purpose of this dissertation is to present four novel studies which examine specific limitations on (1) the pulmonary system (i.e. lungs and circulation) within the highly athletic Thoroughbred horse (Studies A & B), and (2) within the peripheral circulation (i.e. microcirculation) within a disease model of Type II diabetes, the Goto-Kakizaki (GK) rat (Studies C & D). Study A demonstrates that locomotory respiratory coupling (LRC) is not requisite for the horse to achieve maximal minute ventilation (VE) during galloping exercise because VE remains at the peak exercising levels over the first ~13 s of trotting recovery (VE at end exercise: 1391±88; VE at 13 s: 1330±112 L/sec; P > 0.05). The horse also experiences exercise-induced pulmonary hemorrhage (EIPH) which has been linked mechanistically to increased pulmonary artery pressure (Ppa) during high intensity exercise. Therefore, in Study B, we hypothesized that endothelin-1 (ET-1), a powerful vasoconstricting hormone, would play a role in the augmented Ppa and therefore, EIPH. However, contrary to our hypothesis, an ET-1 receptor antagonist did not decrease Ppa nor prevent or reduce EIPH. Studies C and D examine potential mechanisms behind the exercise intolerance observed in humans with Type II diabetes. Utilizing phosphorescence quenching techniques (Study C) within the GK spinotrapezius muscle, we found lowered microvascular PO2 (PO2mv; Control: 28.8±2.0; GK: 18.4±1.8 mmHg; P<0.05) at rest and a PO2mv “undershoot” during muscle contractions. After conducting intravital microscopy within the same muscle (Study D), we discovered the percentage of RBC-perfused capillaries was decreased (Control: 93±3; GK: 66±5 %; P<0.05) and all three major hemodynamic variables (i.e. RBC velocity, flux, and capillary tube hematocrit) were significantly attenuated. Both studies (C & D) indicate that there is reduced O2 availability (via decreased O2 delivery; i.e. ↓QO2/VO2) within Type II diabetic muscle.

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’imagerie fonctionnelle cérébrale détecte les changements hémodynamiques induits par un stimulus pour déterminer les zones d’activation neuronale. Plus particulièrement, l’imagerie BOLD en IRMf détecte les changements d’oxygénation du sang grâce aux propriétés paramagnétiques de la déoxyhémoglobine. L’oxygène n’est donc pas uniquement un substrat énergétique pour le tissu neuronal, il joue également un rôle majeur dans l’imagerie noninvasive du cerveau humain. Au cours de ma thèse, j’ai tout d’abord participé à la mise au point d’une nouvelle technique non-invasive d’imagerie de l’oxygène dans le cerveau d’animaux anesthésiés. Couplant un nouveau senseur phosphorescent de l’oxygène (Finikova et al., 2008) et la microscopie biphotonique, cette approche permet à la fois de cartographier l’oxygène en 3D avec une résolution spatiale et temporelle jusqu’alors inégalée, mais aussi de suivre simultanément l’oxygène et le flux sanguin dans les capillaires cérébraux au repos ou lors d’une activation neuronale (Lecoq et al., 2011). Tirant profit des nouvelles possibilités de cette technique, nous avons alors démontré: • la présence d’un shunt artério-veineux uniquement basé sur la diffusion de l’oxygène. Ce résultat, obtenu chez le rat dans la couche la plus superficielle du bulbe olfactif: la couche du nerf (ONL), confirme que l’oxygène ne diffuse pas uniquement à partir des capillaires et démontre que les artérioles contribuent significativement à l’oxygénation du tissu cérébral. Il démontre également qu’il n’est pas possible de déterminer ni la Po2 capillaire ni la Po2 tissulaire à partir de la Po2 veineuse. • l’existence de transitoires de Po2 associés à chaque globule rouge dans le compartiment capillaire, appelés EATs (erythrocyte-associated transients) (Hellums, 1977; Cabrales and Intaglietta, 2007). En bref, de part leur diamètre supérieur à celui de la lumière d’un capillaire, les globules rouges passent un à un dans la lumière des capillaires, laissant entre eux un espace de plasma. Cependant, la faible solubilité de l’oxygène dans le plasma crée une barrière à la diffusion, ce qui se traduit par une inhomogénéité de la Po2 capillaire: celle-ci est élevée au bord du globule rouge et décroit avec la distance pour atteindre un minimum à mi-distance entre deux globule rouges. Poursuivant l’étude des EATs (Parpaleix et al., 2013), nous avons observé les points suivants: • La Po2 tissulaire dans l’environnement immédiat d’un capillaire peut être déterminée à partir de la Po2 vasculaire à mi-distance entre deux érythrocytes. Ce résultat est intéressant en ce qu’il permettra d’effectuer des mesures non invasives de Po2 tissulaire, utile notamment chez l’animal éveillé. • L’amplitude des EATs est si large (35 mmHg en moyenne) que la Po2 capillaire moyenne ne reflète en rien la saturation en oxygène de l’hémoglobine. • Une empreinte filtrée des EATs vasculaires est détectable dans le tissu (_5 mmHg d’amplitude). • Au cours d’une stimulation neuronale, une diminution de la Po2 capillaire moyenne peut être détectée avant l’hyperémie fonctionnelle, un résultat jusqu’à présent controversé dans le domaine de l’imagerie BOLD en IRMf, mais important en ce que ce dip pourrait être un rapporteur très résolutif de l’activation neuronale. Parmi les questions restant en suspens et pouvant être étudiées finement avec notre approche, j’en citerai une principale: quel est le poids des différents facteurs (métaboliques, présynaptiques ou post-synaptiques) et du flux sanguin dans l’établissement de la Po2 cérébrale au repos? / In humans, functional mapping of brain activity mainly relies on the increase of cerebral blood flow (CBF) triggered by neuronal activation. This neurovascular coupling provides energy substrates such as oxygen and glucose to the activated area. The steady state concentration of oxygen, as well as its dynamics upon neuronal activation, have been investigated with numerous methods, however, none of them provided highly resolute measurements in depth. During my PhD, we combined a phosphorescence quenching approach with two-photon microscopy to detect, in depth and with a micrometer spatial resolution scale, the emission of phosphorescence by PtP-C343, a new oxygen nano-sensor designed for two-photon excitation. We first characterized the technique and then reported two biological results, using the olfactory bulb (OB) glomerulus as a model to study oxygen concentration, at rest and upon odor stimulation. We found an arterio-venous shunt, purely based on diffusion, in the superficial nerve layer of the OB, confirming the role of arterioles in brain oxygenation. Simultaneous measurements of Po2 and blood flow allowed us to reveal the presence of erythrocyte-associated transients (EATs), i.e. Po2 fluctuations that are associated with individual erythrocytes. Pursuing the investigation of EAT characteristics, we found that in capillaries, Po2 at mid-distance between two erythrocytes is at equilibrium with, and thus reports Po2 in the nearby neuropil. Finally, we could observe that even in capillaries, a small oxygen initial dip can be detected prior to functional hyperemia, upon odor activation.