Light-dependent reactions | EPFL Graph Search

Light-dependent reactions is jargon for certain photochemical reactions that are involved in photosynthesis, the main process by which plants acquire energy. There are two light dependent reactions, the first occurs at photosystem II (PSII) and the second occurs at photosystem I (PSI), PSII absorbs a photon to produce a so-called high energy electron which transfers via an electron transport chain to cytochrome b6f and then to PSI. The then-reduced PSI, absorbs another photon producing a more highly reducing electron, which converts NADP+ to NADPH. In oxygenic photosynthesis, the first electron donor is water, creating oxygen (O2) as a by-product. In anoxygenic photosynthesis various electron donors are used. Cytochrome b6f and ATP synthase work together to produce ATP (photophosphorylation) in two distinct ways. In non-cyclic photophosphorylation, cytochrome b6f uses electrons from PSII and energy from PSI to pump protons from the stroma to the lumen. The re

Copper-catalyzed transformations of carboradicals generated by electrochemical and photochemical methods: oxidative amination and polyfluoroarylation

Xiangli Yi

Organic radicals are highly active species that can undergo various transformations. Electrochemistry and photochemistry are efficient methods for the generation of these species of high energy, through single electron transfer processes under mild conditions. These methods have been frequently used to form various carboradical intermediates, for example, via the addition of N-centered radicals to alkenes (Section 1.4). Copper is a versatile transition metal that can transform carboradicals for the formation of various chemical bonds (Section 1.6). Combining electrochemistry or photochemistry for the generation of carboradicals with the copper-catalyzed carboradical functionalization will potentially lead to a large chemical space of useful organic reactions. So far, this intersection of electrochemistry or photochemistry with copper chemistry is still highly underdeveloped. In this thesis, we have developed three useful reactions, testifying the practicability of this concept.In Chapter 2, we describe an intramolecular oxidative amination reaction by integrating electrochemical oxidation with Cu catalysis. Electrochemical oxidation facilely generates N-radical from N-H for the intramolecular cyclization to double bonds, and then the resultant carboradicals are transformed into a new double bond via copper-catalyzed oxidative elimination (Section 1.6.1). A wide range of 5-membered N-containing heterocycles bearing a pendant, functionalizable alkene moiety can be synthesized under mild conditions. Mechanistic studies revealed that direct oxidation on the electrode couldn't efficiently convert primary and secondary alkyl radical intermediates into alkenes, and that the assistance of copper was indispensable.In Chapter 3, an intermolecular oxidative amination reaction of unactivated alkenes by integrating photoredox with Cu catalysis is described. This method relied on photochemical reduction of a hydroxyamine derivative to generate amidyl radical which then adds to unactivated alkenes. The obained carboradicals are trapped by the copper catalyst to form allylic amines. The reaction exhibited a broad scope and excellent tolerance for functional groups including highly polar groups. In Chapter 4, we report a decarboxylative coupling reaction of aliphatic acids with polyfluoroaryl nucleophiles by integrating photoredox with copper catalysis. A set of polyfluoroaryl zinc reagents were prepared and applied to the coupling. The aliphatic esters of N-hydroxyphthalimide (NHPI esters) were transformed into alkyl radicals by photoreduction. Then, the trapping of the radical by the copper catalyst and subsequent reductive elimination render the alkyl polyfluoroarenes as products. This method allows the installation of polyfluoroaryls with variable F-content (2F -5F) and F-substitution patterns on primary or secondary alkyl groups, with good compatibility of functional groups. In summary, this thesis demonstrates the combination of electrochemistry and photochemistry with copper catalysis to construct useful synthetic methods. Considering the diversity of radicals that could be generated by electrochemical and photochemical methods, and the versatility of copper catalyzed functionalization of carboradicals, we believe that this combination has far more potential than these three reactions.

EPFL2021

Accumulation in fed-batch reactor with multiple reaction scheme

Charles Ibrahim Guinand

Nowadays, the fine chemical industry requires increasingly faster time-to-market as well as economically efficient and safe processes. In addition, the growing product variety needs more versatile production plants able to produce from small amounts up to several hundred tons per year. As a consequence, the time devoted to development is limited, and the production often takes place in multipurpose plants. This implies that a given process can run in different reactors making the process development a long and complicated task. As a matter of fact, the behaviour of a reactive system changes with scale and also changes from one equipment to another which often leads to difficulties in controlling a reactor at the industrial scale. In most cases, chemical incidents are caused by loss of control and wrong assessment of the thermal potential, resulting in runaway reactions or deviations in different units. These incidents could be foreseen and avoided or at least decreased with an appropriate process development and risk assessment. All processes should be optimised to achieve a fair productivity and still remain inherently safe. Such process characterization aims at providing a better understanding of reaction pathways and thermal behaviour. To reach this goal, save resources and effort, the real system dynamics can be reproduced by models where parameters are estimated from experimental calorimetric data. The dynamic behaviour of the reaction system can be represented by two models: 1) The reaction kinetics, based on an assumption of the reaction scheme considering different reactions occurring along the process course and 2) The reactor dynamics highlighting how the heating/cooling system controls the reaction course by adjusting its temperature and the adopted feed profile strategy. To acquire enough knowledge on the studied reaction system, several experiments have to be performed in a multiscale based approach to maximize the disturbances and explore the overall reaction kinetics. Nevertheless, even with this method, the investigation can be very long due to the increasingly complex models, involving a large number of parameters and amount of experiments. Therefore, a new approach to solve these issues has to be developed. The proposed approach is summarized in three steps: 1. Reaction Kinetic Investigation: Planning and minimize the number of experiments in a statistically optimal way to cover the experimental space efficiently and using a numerical method to extract the reaction kinetics based on the power rate law. 2. Reactor Dynamic Investigation: Planning the experiments in order to obtain information about the dynamic behaviour of the jacket together with its temperature controller and then use a numerical method to extract the parameters representing the reactor. 3. Risk assessment and Optimization: Combine the reaction kinetics and reactor dynamics to shape a Process Implementation model serving to predict the behaviour of the overall system and identify the optimal operating conditions the process inherently safe. This research establishes a new process scale-up methodology, regarding the assessment of the thermal potential. The results demonstrate that a multiscale approach joined with modelling and inherent safety, lead to a better understanding of the system. This approach also notably helps to optimise the operating conditions making the process inherently safe and remaining economically favourable.

EPFL2017

Photo-physical Properties of Perovskites on Curved Surfaces

Konstantins Mantulnikovs

Organic-inorganic metal halide perovskites (MHPs) have recently attracted increasing attention as highly-efficient light-harvesting materials for photovoltaic applications. The technical ease of solution processing of these materials is one of their major advantages on the route towards fabrication of low-cost solar cells and optoelectronic devices. However, the precise control of crystallization and morphology of MHPs deposited from solutions, considered crucial for enhancing the final photovoltaic performance, still remains challenging. Firstly, the PhD thesis focuses on novel and thus far unexplored issues of crystallization mechanisms and photo-physical characterization of polycrystalline MAPbI3 and MAPbBr3 coated via one-step solution processing onto the surface of elongated, cylinder-shaped, quartz substrates with unprecedentedly high curvatures (diameters of 80 to 1800 ÎŒm). The obtained results are then compared with the ones gathered for deposits of polycrystalline MAPbI3 and MAPbBr3 on planar substrates. Secondly, the deposits of polycrystalline MAPbI3 and MAPbBr3 on cylindrical substrates are used to track the changes in photoluminescence (PL) and photocurrent (PC) of these materials in the presence of various gaseous media. In particular, the advantages offered by small cross-sectional dimensions and the cylindrical geometry of thus obtained deposits of MAPbI3 and MAPbBr3 made it possible to easily combine them with simple gas-flow observation chambers having both optical and electrical accesses. This approach enabled to perform simultaneous measurements of PL and PC for polycrystalline deposits of MAPbI3 and MAPbBr3 exposed to the precisely controlled flow of different gaseous media, including technologically important oxygen (O2) and nitrogen (N2). Thus, an insight could be gained into the role and importance of surface defects for the general optoelectronic properties, such as photo-brightening and photo-bleaching, as well as long-term stability of these materials. Thirdly, a study of selective photo-bleaching of MAPbI3 under illumination with specific wavelengths is performed. For the first time this type of experiments were performed under precisely controlled atmosphere of either O2 or N2, additional insight could be gained on the influence of these gaseous media on the mechanism of selective, wavelength-dependent photo-bleaching in MAPbI3. Lastly, a study of the photo-induced charge transfer in a model system of the MAPbI3/TiO2 interface is carried out. Specifically, a contactless technique based on a combination of low-temperature electron spin resonance (ESR) with in situ illumination is used to directly track the photo-carriers at the MAPbI3/TiO2 interface. In particular, this approach shows that the ESR signal intensity of paramagnetic defects in TiO2 (Ti3+-related centers) markedly changes upon illumination of the MAPbI3/TiO2 interface. It is then inferred that the presented novel methodology can be used to monitor the flow of light-excited electrons from MAPbI3 to TiO2. Altogether, in addition to exploring morphological and photo-physical aspects of thin polycrystalline films of two archetypal MHPs, that is MAPbI3 and MAPbBr3, coated onto strongly curved substrates, this PhD dissertation also provides a novel approach for designing MHPs-based devices. In particular, it paves the way for designing sensitive differential gas sensors, which are expected to function under various environmental conditions.

EPFL2019