Coupling Chromophores to Metal and Semiconductor Nanoparticles for Energy Conversion

In this thesis work, we have investigated the interaction between molecular species and nanoparticles to realize organic-inorganic architectures able to perform complex photophysical and photoelectrochemical functions. In a first study, we have coupled an organic oligomer to silicon nanoparticles, demonstrating the ability of this system to act as a light harvesting antenna, considerably enhancing the ability of silicon nanoparticles to exploit visible light to generate its typical very long lived excited state. The high two photon absorption coefficient of the dye allows the system to be excited by NIR femtosecond pulsed light, improving the applicability of the system in high-resolution bioimaging applications. In a second study, we have performed the synthesis of a family of red-NIR emissive zinc complexes of benzodipyrrins, a little explored class of compounds, with the goal of a future integration with silicon nanoparticles to realize advanced photoactive systems. The complexes show good absorption and emission properties in an highly interesting spectral region for bioimaging and solar energy conversion. Moreover, a serendipitous chemical transformation has been observed and investigated, demonstrating its value to access a completely novel class of4 luminescent compounds. Finally, a supramolecular system composed of platinum nanoparticles coupled to a photoactive dendrimer has been synthesized and characterized, proving its ability to drive the evolution of hydrogen from water upon photoirradiation. This novel approach, thanks to the close spatial arrangement of the different components of a photosynthetic system (from the light absorbing units to the catalyst), opens the way to the realization of efficient systems with a wide variety of chromophores (exploiting the well developed chemistry of dendrimeric systems). This strategy overcomes the typical problems of diffusion based approaches, such as the necessity to use long-lived phosphorescent compounds containing expensive metals and the need of electron relays to transport electrons between the photosensizer and the catalyst

Simultaneous dynamic glucose-enhanced (DGE) MRI and fiber photometry measurements of glucose in the healthy mouse brain

Glucose is the main energy source in the brain and its regulated uptake and utilization are important biomarkers of pathological brain function. Glucose Chemical Exchange Saturation Transfer (GlucoCEST) and its time-resolved version Dynamic Glucose-Enhanced MRI (DGE) are promising approaches to monitor glucose and detect tumors, since it is radioactivity-free, does not require 13C labelling and it is easily translatable to the clinics. The main principle of DGE is clear. However, what remains to be established is to which extent the signal reflects vascular, extracellular or intracellular glucose. To elucidate the compartmental contributions to the DGE signal, we coupled it with FRET-based fiber photometry of genetically encoded sensors, a technique that combines quantitative glucose readout with cellular specificity. The glucose sensor FLIIP was used with fiber photometry to measure astrocytic and neuronal glucose changes upon injection of D-glucose, 3OMG and L-glucose, in the anaesthetized murine brain. By correlating the kinetic profiles of the techniques, we demonstrate the presence of a vascular contribution to the signal, especially at early time points after injection. Furthermore, we show that, in the case of the commonly used contrast agent 3OMG, the DGE signal actually anticorrelates with the glucose concentration in neurons and astrocytes. Keywords: fiber photometry; genetically encoded sensors; glucoCEST; kinetic modelling; two-photon microscopy

Measurement of cerebral oxygen pressure in living mice by two-photon phosphorescence lifetime microscopy

The ability to quantify partial pressure of oxygen (pO2) is of primary importance for studies of metabolic processes in health and disease. Here, we present a protocol for imaging of oxygen distributions in tissue and vasculature of the cerebral cortex of anesthetized and awake mice. We describe in vivo two-photon phosphorescence lifetime microscopy (2PLM) of oxygen using the probe Oxyphor 2P. This minimally invasive protocol outperforms existing approaches in terms of accuracy, resolution, and imaging depth

Deficits in mitochondrial TCA cycle and OXPHOS precede rod photoreceptor degeneration during chronic HIF activation

Background: Major retinal degenerative diseases, including age-related macular degeneration, diabetic retinopathy and retinal detachment, are associated with a local decrease in oxygen availability causing the formation of hypoxic areas affecting the photoreceptor (PR) cells. Here, we addressed the underlying pathological mechanisms of PR degeneration by focusing on energy metabolism during chronic activation of hypoxia-inducible factors (HIFs) in rod PR. Methods: We used two-photon laser scanning microscopy (TPLSM) of genetically encoded biosensors delivered by adeno-associated viruses (AAV) to determine lactate and glucose dynamics in PR and inner retinal cells. Retinal layer-specific proteomics, in situ enzymatic assays and immunofluorescence studies were used to analyse mitochondrial metabolism in rod PRs during chronic HIF activation. Results: PRs exhibited remarkably higher glycolytic flux through the hexokinases than neurons of the inner retina. Chronic HIF activation in rods did not cause overt change in glucose dynamics but an increase in lactate production nonetheless. Furthermore, dysregulation of the oxidative phosphorylation pathway (OXPHOS) and tricarboxylic acid (TCA) cycle in rods with an activated hypoxic response decelerated cellular anabolism causing shortening of rod photoreceptor outer segments (OS) before onset of cell degeneration. Interestingly, rods with deficient OXPHOS but an intact TCA cycle did not exhibit these early signs of anabolic dysregulation and showed a slower course of degeneration. Conclusion: Together, these data indicate an exceeding high glycolytic flux in rods and highlight the importance of mitochondrial metabolism and especially of the TCA cycle for PR survival in conditions of increased HIF activity

Aggregation induced phosphorescence of metal complexes: From principles to applications

Metal complexes are the prototypes of phosphorescent materials, widely used in a range of optoelectronic and sensing applications. This review reports the most recent and tutorial results in the area of aggregation induced phosphorescence (AIP) of metal complexes, i.e. molecules that are weakly or non-phosphorescent in deaerated fluid solution and whose room temperature phosphorescence is switched on upon aggregation. The examples are divided into two main classes according to the AIP mechanism: (i) rigidification that causes a restriction of intramolecular motions as well as of structural distortion of the phosphorescent excited state and (ii) metallophilic interaction that brings about new electronic transitions compared to the isolated chromophores. The last section is devoted to a special class of molecules and supramolecular systems, in which metal complexation turns on phosphorescence of nearby organic chromophores, so that the metal complex is not directly involved in the phosphorescence process

NIR-emissive iridium(III) corrole complexes as efficient singlet oxygen sensitizers

Three new iridium(III) corrole complexes, having symmetrically and asymmetrically substituted corrole frameworks and judiciously varied axial ligands are prepared and characterized by various spectroscopic techniques including the X-ray structures of two of them. The observed phosphorescence at ambient temperature appears at much longer wavelengths than the previously reported Ir(III) porphyrin/corrole derivatives. Efficiencies of these compounds in the generation of singlet oxygen are also studied for the first time

Simultaneous dynamic glucose-enhanced (DGE) MRI and fiber photometry measurements of glucose in the healthy mouse brain

Glucose is the main energy source in the brain and its regulated uptake and utilization are important biomarkers of pathological brain function. Glucose Chemical Exchange Saturation Transfer (GlucoCEST) and its time-resolved version Dynamic Glucose-Enhanced MRI (DGE) are promising approaches to monitor glucose and detect tumors, since they are radioactivity-free, do not require 13C labeling and are is easily translatable to the clinics. The main principle of DGE is clear. However, what remains to be established is to which extent the signal reflects vascular, extracellular or intracellular glucose. To elucidate the compartmental contributions to the DGE signal, we coupled it with FRET-based fiber photometry of genetically encoded sensors, a technique that combines quantitative glucose readout with cellular specificity. The glucose sensor FLIIP was used with fiber photometry to measure astrocytic and neuronal glucose changes upon injection of D-glucose, 3OMG and L-glucose, in the anaesthetized murine brain. By correlating the kinetic profiles of the techniques, we demonstrate the presence of a vascular contribution to the signal, especially at early time points after injection. Furthermore, we show that, in the case of the commonly used contrast agent 3OMG, the DGE signal actually anticorrelates with the glucose concentration in neurons and astrocytes.ISSN:1053-8119ISSN:1095-957

Photoactive Dendrimer for Water Photoreduction: A Scaffold to Combine Sensitizers and Catalysts

We report on the synthesis and characterization of platinum nanoparticles (PtNps) inside the cavities of a PAMAM dendrimer decorated with [Ru­(bpy)₃]²⁺ units at the periphery. The phosphorescent ruthenium complexes are used as signaling units of the Pt²⁺ complexation in the dendritic architecture and as photosensitizer units in the photocatalytic production of H₂ from water. This is the first example of water photoreduction in which the catalyst and the sensitizer are anchored on a dendritic molecular scaffold. This study provides a new outlook in the design of new supramolecular systems and materials for developing artificial photosynthesis

Controlled Functionalization of Reduced Graphene Oxide Enabled by Microfluidic Reactors

We report the use of microfluidics to functionalize suspended reduced graphene oxide flakes through the addition of aryl radical, generated in situ by reaction between aryl amines and isopentyl nitrite. Microfluidic enabled a tight control of temperature, reaction times, and stoichiometric ratios, making it possible to tune the growth of oligomers on the surface of the flakes, which in turn affects the interactions of the functional material with the surrounding environment. The results suggest that shear stress phenomena within the reactor may play a role in the chemistry of graphene materials by providing a constant driving force toward exfoliation of the layered structures. Scale-up of the functionalization process is also reported along with the grafting of dyes based on squaric acid cores. Photophysical characterization of the dye-modified flakes proves that the microfluidic approach is a viable method toward the development of new materials with tailored properties