The efficiency and mechanism of electron- and energy transfer events occurring in both in natural and synthetic donor-acceptor systems depend on their distance, relative orientation, and the nature of the surrounding media. Fundamental knowledge gained from model studies is key in building efficient energy harvesting and optoelectronic devices. Faster charge separation and slower charge recombination in donor-acceptor systems is often sought out. In our continued effort to build donor-acceptor systems using near-IR sensitizers, in the present study, we report ground and excited state charge transfer in newly synthesized, directly linked, tetrads featuring bisdonor (donor = phenothiazine and ferrocene), BF2-chelated azadipyrromethane (azaBODIPY) and C60 entities. The tetrads synthesized using multi-step synthetic procedure revealed strong charge transfer interactions in the ground state involving the donor and azaBODIPY entities. The near-IR emitting azaBODIPY acted as a photosensitizing electron acceptor along with fullerene while the phenothiazine and ferrocene entities acted as electron donors. The triads (bisdonor-azaBODIPY) and tetrads revealed ultrafast photoinduced charge separation leading to D•+-azaBODIPY•–-C60 and D•+-azaBODIPY-C60•– (D = phenothiazine or ferrocene) charge separated states from the femtosecond transient absorption spectral studies in both polar and nonpolar solvent media. The charge separated states populated the triplet excited state of azaBODIPY prior returning to the ground state.

Real-time systems are composed of a set of tasks that must respect some deadlines. We find them in applications as diversified as the telecommunications, medical devices, cars, planes, satellites, military applications, etc. Missing deadlines in a real-time system may cause various results such as a diminution of the quality of service provided by the system, the complete stop of the application or even the death of people. Being able to prove the correct operation of such systems is therefore primordial. This is the goal of the real-time scheduling theory.<p><p>These last years, we have witnessed a paradigm shift in the computing platform architectures. Uniprocessor platforms have given place to multiprocessor architectures. While the real-time scheduling theory can be considered as being mature for uniprocessor systems, it is still an evolving research field for multiprocessor architectures. One of the main difficulties with multiprocessor platforms, is to provide an optimal scheduling algorithm (i.e. scheduling algorithm that constructs a schedule respecting all the task deadlines for any task set for which a solution exists). Although optimal multiprocessor real-time scheduling algorithms exist, they usually cause an excessive number of task preemptions and migrations during the schedule. These preemptions and migrations cause overheads that must be added to the task execution times. Therefore, task sets that would have been schedulable if preemptions and migrations had no cost, become unschedulable in practice. An efficient scheduling algorithm is therefore an algorithm that either minimize the number of preemptions and migrations, or reduce their cost.<p><p>In this dissertation, we expose the following results:<p>- We show that reducing the "fairness" in the schedule, advantageously impacts the number of preemptions and migrations. Hence, all the scheduling algorithms that will be proposed in this thesis, tend to reduce or even suppress the fairness in the computed schedule.<p><p>- We propose three new online scheduling algorithms. One of them --- namely, BF2 --- is optimal for the scheduling of sporadic tasks in discrete-time environments, and reduces the number of task preemptions and migrations in comparison with the state-of-the-art in discrete-time systems. The second one is optimal for the scheduling of periodic tasks in a continuous-time environment. Because this second algorithm is based on a semi-partitioned scheme, it should favorably impact the preemption overheads. The third algorithm --- named U-EDF --- is optimal for the scheduling of sporadic and dynamic task sets in a continuous-time environment. It is the first real-time scheduling algorithm which is not based on the notion of "fairness" and nevertheless remains optimal for the scheduling of sporadic (and dynamic) systems. This important result was achieved by extending the uniprocessor algorithm EDF to the multiprocessor scheduling problem. <p><p>- Because the coding techniques are also evolving as the degree of parallelism increases in computing platforms, we provide solutions enabling the scheduling of parallel tasks with the currently existing scheduling algorithms, which were initially designed for the scheduling of sequential independent tasks. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Une nouvelle famille de complexes de difluorure de bore photosensibles est développée. Elle est basée sur des structures moléculaires contenant une unité β-dicétone à conjugaison électronique π.La grande variété de groupements aromatiques et la nature donneur ou accepteur d'électrons des différents substituants permet l'élaboration de systèmes électroniques donneur-accepteur-donneur d'électrons (D1-A-D1) et donneur-accepteur (D2-A).L'absorption électronique de cette famille de molécule se situe dans la partie visible du spectre électromagnétique et une partie du spectre ultraviolet, et est caractérisée par une bande d'absorption π-π* intense avec des coefficients d'absorption molaire supérieurs à 50 000 M-1cm-1.L'émission de fluorescence couvre une plage spectrale qui va du visible au proche infrarouge avec des rendements quantiques de fluorescence en solution relativement élevés pouvant atteindre 62 %.En fin, cette famille de molécule est photochimiquement stable et est, contrairement à d'autres familles de complexes de difluorure de bore, chimiquement très stable en solution.Mots-clés : Difluorure de bore, β-dicétone, matériaux π-conjugués, luminescence, fluorescence stationnaire et résolue dans le temps (TRES), synthèse organique, RMN-19F dynamique, complexes & colorants fluorescents, curcumine & curcuminoide, complexe BF2, photophysique. / A new photosensitive family of boron difluoride complex is developed. It is based on π-conjugated molecular structures containing β-diketonates unit.The wide variety of aromatic groups and the nature of donor or electron acceptor of the different substituents allow the development of electron donor-acceptor-donor (DAD) and donor-acceptor (DA) electronic systems.The electronic absorption of this family of molecules is in the visible part of the electromagnetic spectrum and a portion of the ultraviolet spectrum, and is characterized by an intense π-π* absorption band with molar absorption coefficient greater than 50 000 M-1.cm-1.The fluorescence emission covers a spectral range going from visible to near infrared, with relatively high fluorescence quantum yields of up to 62 % in solution.This new material family is photochemically stable and, unlike some other families of boron difluoride complexes, chemically very stable in solution.