Polypyridyl transition metal complexes containing ruthenium, rhodium and iridium centers are mainly studied due to their light absorbing and emitting properties. Lanthanide oxides such as europium oxide absorb light as well and exhibit strong luminescence and long lifetimes. The optical properties of these materials were significant especially in solar energy utilization schemes and optical applications. Energy transfer across a surface is important in several applications including phosphors and biomedical applications. Excited states of metal complexes with a carboxylate-containing ligand such as deeb = diethyl-2,2'-bipyridine-4,4'-dicarboxylate were studied on nanoparticle surfaces. In this work, [Rh(deeb)2Cl2](PF6), [Ir(deeb)2Cl2](PF6) and [Ir(deeb)2(dpp)](PF6)3 were synthesized using the building block approach. The metal complexes were characterized using 1H NMR spectroscopy, mass spectrometry, electronic absorption spectroscopy and electrochemistry. The 1H NMR spectra of the complexes were consistent with those of their ruthenium analogs. Mass spectra contain fragmentation patterns of the (M-PF6)+ molecular ion for [Rh(deeb)2Cl2](PF6) and [Ir(deeb)2Cl2](PF6), and (M-3PF6)3+ molecular ions for [Ir(deeb)2(dpp)](PF6)3. The electronic absorption spectrum of [Rh(deeb)2Cl2](PF6) shows a maximum at 328 nm, which is assigned as 1π→π*transition. The electronic absorption spectrum of [Ir(deeb)2Cl2](PF6) shows maxima at 308 nm and 402 nm, which are assigned as 1π→π* and metal-to-ligand charge transfer transitions, respectively. The [Ir(deeb)2(dpp)](PF6)3 complex exhibits peaks due to 1π→π* transitions at 322 nm and 334 nm. [Rh(deeb)2Cl2](PF6) has emission maxima from the 3LF state at 680 nm and 704 nm for the solid and glassy solutions at 77 K, respectively. [Ir(deeb)2Cl2](PF6) has emission maxima from the 3MLCT state at 538 nm in acetonitrile and 567 nm in the solid state at room temperature, with lifetimes of 1.71 μs and 0.35 μs, respectively. [Ir(deeb)2Cl2](PF6) has an unusually higher quantum yield than analogous compounds. [Ir(deeb)2(dpp)](PF6)3 has emission maxima from the 3IL state at 540 nm in acetonitrile and 599 nm in the solid state at room temperature, with lifetimes of 1.23 μs and 0.14 μs, respectively. Cyclic voltammetry of [Ir(deeb)2Cl2](PF6) and [Ir(deeb)2(dpp)](PF6)3 yield reversible and quasi-reversible couples corresponding to deeb ligand and Ir3+/+reductions, respectively. Attachment of the complexes were conducted by equilibration of complex solutions in acetonitrile with europium oxide nanoparticles. Europium oxide nanoparticles, which were synthesized by gas-phase condensation, have 11-nm diameters and exhibit sharp f-based luminescence in the visible and near IR regions. EDX, TEM, IR and reflectance spectroscopy measurements indicate substantial coating through various modes of attachment of the nanoparticle surface by the metal complexes while retaining the excited state properties of the metal complexes. Surface adsorption studies indicate monolayer coverage of the nanoparticle surface by the metal complexes, consistent with limiting surface coverages of previously reported analogous systems. Eu2O3 nanoparticles modified with [Rh(deeb)2Cl2]+ exhibit minimal to no energy transfer from emission spectra, and a reduction in the lifetime at 77K could be due to the rhodium complex preventing the excitation of Eu3+. Upon attachment of the Ir complexes [Ir(deeb)2Cl2]+ and [Ir(deeb)2(dpp)]3+ on as-prepared nanoparticles, Eu3+ luminescence was observed for nanoparticles modified with iridium complexes at room temperature, which could be due to energy transfer among other possibilities. Efficiencies of 68% and 50%, and energy transfer rate constants of 1.1 x 10-5 and 1.0 x 10-5 were calculated from lifetime data for [Ir(deeb)2Cl2]+ and [Ir(deeb)2(dpp)]3+ on Eu2O3 nanoparticles, respectively. Since iridium complexes are used as components of light-emitting diodes, europium oxide nanoparticles modified with iridium complexes have potential in optical applications which make studies of these compounds interesting. / Master of Science

La fotoquímica supramolecular es una herramienta muy utilizada para controlar la selectividad, la reactividad y el avance de las reacciones químicas. Con ella se aprovecha la estructura tridimensional del anfitrión para canalizar la conformación de los estados excitados de los sustratos que intervienen en la reacción. En la literatura se encuentran numerosos casos de fotorreacciones catalizadas por supramoléculas abióticas, pero los ejemplos con biomoléculas son escasos. En este contexto, el objetivo de la presente tesis ha sido estudiar reacciones fotoquímicas clásicas en el seno de biomoléculas ya que éstas pueden presentar ventajas respecto a las supramoléculas abióticas. Se han escogido las albúminas séricas como anfitriones bióticos, en base a dos propiedades claves: (i) son proteínas transportadoras que actúan como vehículo de una amplia variedad de sustancias; (ii) poseen dos sitios de unión diferenciados: el sitio I y el sitio II. La reorganización de foto-Fries fue la primera reacción abordada. Para ello se diseñaron varios sustratos que interaccionaban en los sitios de unión I y II de distintas albúminas. Distintos estudios cinéticos demostraron que los rendimientos de formación de los fotoproductos dependían del sitio de interacción y de la clase de albúmina utilizada. Se seleccionaron también derivados de avobenzona (AB) sustituídos en la posición ? de los carbonilos. Se demostró que éstos sólo existen bajo su forma ?-dicetónica, la cual puede desencadenar procesos de fototoxicidad. Se estudió mediante fotólisis de destello láser el efecto de la interacción de los tres derivados con HSA y los resultados mostraron el efecto protector de ésta frente al ataque por oxígeno y la auto-desactivación y reflejaron el entorno confinado proporcionado por la albúmina. Además, se investigó la fragmentación de Norrish tipo II de uno de los derivados, que resultó ser más lenta en presencia de albúmina. Por último, se consideró la fotoelectrociclación [6?] de la N- / Marín Melchor, M. (2013). Proteïnes com a microreactors en fotoquímica supramolecular [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/27204

Exposure to ground-level ozone (O₃), which forms secondarily in the atmosphere, intensifies the risk of respiratory and cardiovascular diseases. Effective mitigation strategies require understanding the spatiotemporal variability of O₃ precursors, including nitrogen oxides (NOx) and volatile organic compounds (VOCs), as well as O₃ formation photochemistry. This thesis examines the concentrations of trace gases closely related to O₃ production, specifically nitrogen dioxide (NO₂, the dominant component of NOx) and formaldehyde (HCHO, a proxy for VOC reactivity), as well as photochemical conditions. I investigate how these factors differ on high-O₃ days, change diurnally, and respond to the temporal resolution of anthropogenic emissions. The focus is on the summer of 2018 due to the availability of trace gas retrievals from the TROPOspheric Monitoring Instrument (TROPOMI) and in situ measurements from field campaigns. I first investigate New York City (NYC) and the Baltimore/Washington D.C. area, where high O₃ levels frequently occur in summer. On high-O₃ days (when the maximum daily 8-hour average (MDA8) O₃ exceeds 70 ppb), tropospheric vertical column densities (VCDTrop) of HCHO and NO₂ increase in urban centers. The HCHO/NO2 VCDTrop ratio, proposed as an indicator of local surface O₃ production sensitivity to its precursors, generally rises due to a more pronounced increase in HCHO VCDTrop. This suggests a shift toward a more NOx-sensitive O₃ production regime that could enhance the effectiveness of NOx controls on the highest O₃ days. As retrievals of tropospheric trace gases from Low Earth Orbit (LEO) satellites like TROPOMI are limited to one overpass per day (early afternoon), I then analyze spatial variability in HCHO and NO₂ concentration diurnal patterns and connect changes in column densities with surface concentrations. Diurnal HCHO patterns indicate the impact of temperature-dependent VOC emissions, while a bimodal surface NO₂ pattern reflects diurnal patterns of local anthropogenic NOx emissions and boundary layer dynamics. Column concentration peaks generally occur about four hours after surface concentration peaks (morning for NO2 and midday for HCHO), highlighting the challenge of relating column densities to health-related surface concentrations. I also explore how the temporal resolution of anthropogenic emissions influences air pollution levels and diurnal variations. Surface NOx and O3 concentrations show different spatial patterns of change when switching from daily mean to hourly varying nitric oxide emissions. In urban areas of both the western and eastern CONUS, adding hourly NO emissions increases daytime emissions, leading to O₃ decreases, indicating NOx-saturated O₃ chemistry. In the western CONUS, monthly mean surface NO₂ increases, while in the eastern CONUS, characterized by shorter NO₂ lifetimes, NO₂ decreases. These sensitivities highlight the importance of accounting for diurnal changes when inferring emissions from concentrations. This thesis advances our understanding of O₃-NOx-VOC air pollution by exploring variations in both surface and column conditions across urban-rural gradients. It integrates in situ measurements, space-based observations, and modeling techniques and assesses advanced modeling tools for future applications. These findings support the future applications of geostationary satellite retrievals for continuous trace gas observation throughout daylight hours, supplementing the once-a-day LEO satellite data used in this thesis, with implications such as aiding source attribution and targeting cost-effective control measures for O₃ mitigation.

The production of hydrogen fuel via solar water splitting is an important carbon-neutral strategy for the development of renewable resources and has sparked great interest in the scientific community. Hydrogen production efficiencies for supramolecular photocatalysts of the architecture [{(TL)2Ru(BL)}2RhX2]5+ (BL=bridging ligand, TL=terminal ligand, X=halide) are among the highest reported in deoxygenated organic solvents, but do not function in air-saturated aqueous solution due to quenching of the metal-to-ligand charge transfer (MLCT) excited-state under these conditions. Herein, we report the groundbreaking use of polyelectrolytes to increase efficiency of supramolecular photocatalysts in solar hydrogen production schemes under aqueous aerobic conditions. The new photocatalytic system incorporates poly(4-styrenesulfonate) (PSS) into aqueous solutions containing [{(bpy)2Ru(dpp)}2RhCl2]5+ (bpy = 2,2'-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine). PSS has a profound impact on photocatalyst efficiency, increasing hydrogen production over three times that of deoxygenated aqueous solutions alone. Hydrogen photocatalysis proceeds even under aerobic conditions for PSS containing solutions, an exciting consequence for solar hydrogen production research. Thermodynamics of binding due to intermolecular interactions between Ru,Rh,Ru photocatalysts and polyelectrolytes was probed using isothermal titration calorimetry (ITC). ITC studies reveal the driving forces of aggregate formation, providing new insight into the intermolecular forces that lead to increased photocatalytic efficiency and stability in the presence of water soluble polymers. Synthesis and characterization of a novel supramolecular photocatalyst having hydrophilic terminal ligands are reported. Addition of sulfonated terminal ligands into a Ru,Rh,Ru photocatalyst has a significant impact on the excited-state properties of the complex. The new complex demonstrates increased solubility and hydrogen production efficiency in aqueous solutions. Hydrogen production is observed even under aerobic conditions for the new complex, a stark contrast to the hydrophobic analog in organic solvents. The synthesis, characterization, and electropolymerization of a chromophore-catalyst assembly having vinyl-substituted terminal ligands to create robust water reduction photocatalysts on wide-bandgap semiconductors is reported. The polymeric photocatalysts are expected to show increased stability over a wide pH range and increased photostability compared to chromophore-catalyst assemblies that employ carboxylic or phosphonic acid groups to adsorb the photoreactive catalyst to the metal oxide surface. / Ph. D. / The production of H₂ fuel from water using sunlight is an important carbon-neutral strategy for the development of renewable resources and has sparked great interest in the scientific community. H₂ production efficiencies for light-activated catalysts of the architecture [{(TL)₂Ru(BL)}₂RhX₂]⁵⁺ (BL=bridging ligand, TL=terminal ligand, X=halide) are among the highest reported in deoxygenated organic solvents, but do not function in air-saturated aqueous solution due to deactivation of the catalyst under these conditions. Herein, we report the groundbreaking use of water soluble polymers to increase efficiency of light activated catalysts in solar H₂ production schemes in air-saturated water. The new photocatalytic system incorporates poly(4-styrenesulfonate) (PSS) into aqueous solutions containing [{(bpy)₂Ru(dpp)}₂RhCl₂]⁵⁺ (bpy = 2,2'-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine). PSS has a profound impact on the efficiency of the light activated catalyst, increasing H₂ production over three times that of deoxygenated aqueous solutions alone. H₂ production proceeds even in air-saturated water for PSS containing solutions, an exciting consequence for solar hydrogen production research. Interactions between Ru,Rh,Ru light activated catalysts and polyelectrolytes were probed using isothermal titration calorimetry (ITC). ITC studies reveal the driving forces of aggregate formation, providing new insight into the intermolecular forces that lead to increased efficiency and stability in the presence of water soluble polymers. Synthesis and characterization of a novel light activated catalyst having hydrophilic terminal ligands are reported. Addition of water soluble terminal ligands into a Ru,Rh,Ru light-activated catalyst has a significant impact on the excited-state properties of the molecule in aqueous solution. The new molecule demonstrates increased solubility and H₂ production efficiency in aqueous solutions. H₂ production is observed even under aerobic conditions for the new molecule, a stark contrast to the hydrophobic analog in organic solvents. The synthesis, characterization, and polymerization of a new light activated catalyst on a metal oxide surface is reported. The polymeric light-activated catalysts are expected to show increased stability over a wide pH range and increased stability compared to light-activated catalysts that employ carboxylic or phosphonic acid groups to adsorb the catalyst to the metal oxide surface.

La lignine a le potentiel de devenir une alternative renouvelable à l’utilisation des ressources fossiles. Ce potentiel provient du fait que la chaîne principale de ce biopolymère est riche en motifs aromatiques. La dépolymérisation de la lignine pourrait donc permettre l’obtention de réactifs aromatiques bas en poids moléculaire. Une méthode de dépolymérisation particulièrement prometteuse à cet effet est le clivage photocatalytique du lien β-O-4 de la lignine. Le premier chapitre de ce mémoire offre un bref survol des concepts de la photochimie, de la photocatalyse et de la dépolymérisation catalytique de la lignine. Le second chapitre détaille la mise au point de conditions réactionnelles vertes permettant le clivage du lien β-O-4 dans des modèles de lignine avec de bons rendements. La réaction est photocatalysée par un catalyseur hétéroleptique de cuivre. Lorsqu’effectuée en chimie en flux continu, la réaction conserve son efficacité à l’échelle du gramme. La décomposition photocatalytique d’un polymère modèle est aussi possible grâce aux conditions optimisées. Des études d’extinction permettent de mieux comprendre le mécanisme réactionnel et confirment qu’un co-catalyseur est responsable de la réduction du catalyseur de cuivre excité. / Lignin has the potential to become a renewable alternative to fossil fuels for the industrial production of low molecular weight aromatic compounds. This potential stems from the fact that the lignin biopolymer’s backbone is rich in aromatic moieties, which could theoretically be retrieved through an optimized depolymerization process. One promising technique consists in the photocatalytic cleavage of the β-O-4 linkage of lignin. The first chapter of the thesis offers a brief overview of the concepts of photochemistry, photocatalysis, and of the depolymerization of lignin. The second chapter details the development of green reaction conditions allowing for the cleavage of the β-O-4 linkage in lignin models with good yields. The reaction is photocatalyzed by a heteroleptic copper catalyst. The reaction is also amenable for flow chemistry, whereby it remains as efficient at the gram scale. Photocatalytic decomposition of a model polymer was also possible using the optimized reaction conditions. Quenching studies confirm that a sub-stoichiometric nicotinamide is responsible for the reduction of the excited copper catalyst, giving insight into the reaction’s mechanism.

Charge transfer at the organic/inorganic semiconductor interfaces lies at the heart of interfacial photochemistry. While decades of research have shaped the current understanding that interfacial charge transfer depends crucially on energetic driving force and electronic coupling, much less is known about the role played by the spin degree of freedom. In particular, it is not clear how spin states evolve during the charge transfer process. With the advent of group 6 transition metal dichalcogenides (TMDC), a class of two-dimensional layered materials which permits the optical generation of spin-polarized electron-hole pairs in the monolayer limit, we now have the opportunity to investigate if charge transfer at an organic/inorganic interface could enable the transfer of spin polarization. Using time-resolved Faraday rotation and transient absorption spectroscopy, it is found in the MoSe₂/H₂Pc and C60/WS₂ heterostructures that the photoinduced hole transfer from MoSe₂ to H₂Pc and electron transfer from WS₂ to C60 results in spin polarization lifetimes one order of magnitude longer than that of a monolayer. In the WS₂/MoSe₂/H₂Pc heterostructure, the addition of a WS₂ monolayer drives the dissociation of electron-hole pairs bound at the MoSe₂/H₂Pc interface and leads to the observation of nanosecond-long spin polarization at room temperature. These findings evidence the photoinduced transfer of spin polarization, a mechanism which could potentially be exploited to enhance the efficiency and selectivity of photochemical reactions involving angular momentum change, and may be generalized to other organic/inorganic interfaces composed of crystalline semiconductors with spin-momentum locking.

<p dir="ltr">Aromatic phosphonates and phosphine oxides are highly desirable synthetic targets used in pharmaceuticals, natural products, agrichemicals, catalysis, and materials science. While a variety of aromatic precursors have been used to access these motifs, aryl halides remain one of the most desirable coupling partners owing to their low cost, commercial availability, and regioselective reactivity. Traditional phosphonation often requires the use of harsh reductants in the presence of liquid ammonia, which are caustic and pose incredible environmental concerns. Milder, transition metal-catalyzed approaches have been developed, but can be limited by air sensitivity, cost, low reaction selectivity, and low functional group compatibility. Photoredox catalysis has been significantly advanced in the past decade in the pursuit of greener, more sustainable avenues to facilitate desirable reaction transformations under mild conditions. These methods most commonly use a dual catalytic strategy in which a metal is paired with an organocatalyst. While these approaches enable facile phosphonation of a variety of aromatic precursors, the metals and organocatalysts used are often expensive and toxic. Indeed, there remains unexplored chemical space for transition metal-free photoredox-catalyzed aryl C-P bond formations. Herein, we present a series of transition metal-free, photoredox-catalyzed approaches to the phosphonation of aryl halides. The approaches and mechanistic works will be discussed in the following order: </p><p dir="ltr">First, the discovery that 10<i>H</i>-phenothiazine (PTZ) enables the transition metal-free phosphonation of aryl halides using trialkyl phosphites will be presented. PTZ serves as a photocatalyst capable of reducing the aryl halide to access aryl radicals, which readily couple with phosphite esters. This transformation exhibits broad functional group tolerance in good to excellent yields. Then, photoredox catalysis by PTZ enables the formation of unsymmetrical aromatic phosphine oxides using triphenylphosphine (PPh₃) and aryl halides. This is the first work in which PPh₃ has been used as the starting material, and the reaction proceeds via the alkaline hydrolysis of quaternary phosphonium salts. The final work exhibits novel photocatalytic activity of <i>N</i>-heterocyclic carbenes (NHC) to activate aryl halides, form aryl radicals, and enable phosphonation. This method displays broad functional group tolerance under mild conditions and highlights its untapped synthetic utility as a photocatalyst.</p>

Herein is presented the doctoral research of Logan Rockwell Beck. We first report the development a library of osmium(II) polypyridyl complexes and characterize them for use in photoredox catalysis. We then report a triplet-triplet annihilation upconversion system that produces an oxidizing excited state and exhibits a remarkable 1.25 eV anti-Stokes shift. This upconversion system is then applied to dual nickel/photoredox catalyzed C-O cross-coupling. Finally, we discuss efforts towards the remote arylation of aliphatic amines through 1,5-HAT.

Tightly focused femtosecond laser pulses are widely used in the biomedical field due to their nonlinear multiphoton precision and minimal thermal side effects. Below the threshold of optical breakdown, light energy contributes to photochemical reactions that introduce more chemical bonding in the form of collagen crosslinking (CxL) in extracellular matrices of transparent tissues such as corneal stroma. Previously, based on the principles of ultrafast laser-tissue interaction, a novel collagen CxL method relying on low-density plasma (LDP) generating reactive oxygen species (ROS) was proposed and applied to cornea tissue for vision correction by the Vukelic Group and extended to articular cartilage tissue for early osteoarthritis treatment in collaboration with Musculoskeletal Biomechanics Research Laboratory. Despite the efficiency and safety of the procedure, LDP was elusive and challenging to control due to its potential dependence on a cascade of intertwining factors such as ultrafast laser wavelength, power, pulse duration, repetition rate, and ionization resonance. This thesis has two aims: the first is to investigate the photochemical laser-tissue interaction with femtosecond nanojoule energy pulses, and the second is to develop robust and practical laser parameter envelopes for treating corneal ectatic diseases and osteoarthritis. Chapter 2 proposes a corneal epithelium-stromal level wound healing treatment. Relying on the interaction between reactive oxygen species (ROS) created by low-density plasma (LDP) therapy and inflammatory cytokines, epithelium recovery is accelerated on in vivo rabbit corneas. Chapters 3 to 5 focus on photochemical reaction-based morphological correction and biomechanical enhancement for corneal diseases such as keratoconus and astigmatism. A wavelength-independent, nonenzymatic CxL technique based on oxygen-independent, pentose-mediated glycation and ROS acceleration is developed; collagen CxL efficiency is tested through autofluorescence microscopy and nanoindentation. Subsequently, the combined effects of simultaneous external mechanical loading and nonenzymatic collagen CxL, achieved by both traditional CxL that involves soaking eyes with riboflavin solution, a photosensitizer, and then activating it with ultraviolet A light (UVA-Riboflavin-CxL) and new ROS catalyzed glycation CxL (ROS-Glycation-CxL) techniques, are investigated on ex vivo rabbit corneas. Through X-Ray Diffraction, permanent adjustments to the ultrastructure of collagen fibril packing are observed, ultimately contributing to refractive power changes in corneal topography. Furthermore, with the addition of melanin application that increases absorption and ionization efficiency, a robust method for generating plasma and reactive oxygen species (ROS) is proposed and implemented on ex vivo corneas to address ectatic diseases. Chapter 6 discusses the effect of plasma-guided laser collagen CxL on articular cartilages’ compressive equilibrium modulus and chondrocyte viability. Stemming from the melanin-assisted protocol and ultrafast pulses' high peak power, a plasma spark-mediated laser treatment is hypothesized to biomechanically enhance both bovine and human articular cartilage superficial zone for the treatment of osteoarthritis. Chapter 7 concludes this thesis and proposes future directions.

As traditional solar technologies approach theoretical efficiency limits, novel approaches are necessary to continue to improve the power generation capacity of photovoltaics. Two complementary multiexcitonic processes, singlet fission (SF) and triplet-triplet annihilation upconversion (TTA-UC), show great promise in this field, allowing access to regions of the solar spectrum inefficiently harvested by silicon cells. In designing and optimizing systems for SF and TTA-UC, macromolecular scaffolds are particularly attractive, enabling the simultaneous tuning of electronic coupling between chromophores as well as their intermolecular packing. The high modularity of these scaffolds allows for easy adjustment of component ratios or the introduction of new units to further adjust dynamics or morphology. As such, macromolecular systems have also been employed in various condensed and solid phase systems which may more readily be incorporated into photovoltaics. Herein, we expand the scope of macromolecular architectures to new domains for SF and TTA-UC. In Chapter 1, we summarize the guiding principles for the optimization of these processes, and follow with a discussion of existing oligomeric, macromolecular, and self-assembled systems. In Chapter 2, an amphiphilic block copolymer (BCP) is introduced to explore SF in self-assembled micelles. We find that SF dynamics can be controlled by modifying BCP block ratios, as well as by co-assembly with a variety of dopants. In Chapter 3, this amphiphilic BCP scaffold is adapted to TTA-UC, and we highlight the importance of micellar swelling in enabling this process. In Chapter 4, electron donors are incorporated into polymers alongside pendent SF chromophores to explore both intra- and intermolecular charge transfer. We observe the formation of long-lived charge separated states prompted by SF, with dynamics tunable by solvent polarity, donor strength, and mode of interaction. And in Chapter 5, a series of hetero-oligomers are presented to explore SF at interfaces between classic acenes and the less-studied dipyrrolonaphthyridinedione. We reinforce the essential role of charge transfer states in mediating or deactivating singlet fission in a tunable fashion based on chromophore energetics. In sum, this work further demonstrates the essential role macromolecular engineering will play in the continued development of SF and TTA-UC.