Novel Avenues Toward Controlling the Photophysical Properties of Ultra-Small Silicon Quantum Dots

Quantum dots (QDs) have attracted an increasing attention in the last decade over many conventional organic dyes. This is due to their unique optical properties including broad absorption spectra, high photostability, and size-tunable photoluminescence (PL). However, some toxicity concerns associated with traditional quantum dots have hindered their wide applicability. Interestingly, silicon quantum dots (SQDs) have been shown to be more advantageous than most of QDs thanks to their excellent biocompatibility and biodegradability, low cytotoxicity, and versatile surface functionalization capability. Thus, SQDs are promising candidates for various biological and biomedical applications such as bioimaging, biosensing, and photodynamic therapy. Unfortunately, only a few studies in literature investigated factors that impact the optical properties of SQDs. In this thesis, we studied the impact of functionalization of ultra-small SQDs (\u3c 2 nm diameter) with different aromatic fluorophores and/or spacers as a means to control their optical properties. We first functionalized the SQDs with phenanthrene, pyrene, and perylene fluorophores through a conjugated spacer which led to an efficient energy transfer from the fluorophores to the SQDs core. As a result, the photoluminescence of the SQDs was red- or blue-shifted and its emission quantum efficiency (QE) was moderately enhanced depending on the fluorophore type. Furthermore, we investigated the impact of different spacers, e.g. N-propylurea and propylamine spacers, on controlling the optical properties of SQDs in which perylene dye was utilized as the capping agent. The nature of spacer played a vital role influencing the interaction of the aromatic dye with the electronic wave function of SQDs. Energy transfer was proven to be the predominant process when propylurea spacer was utilized, while propylamine spacer was found to facilitate electron transfer process. Finally, SQDs were functionalized with different fluorescein and rhodamine derivatives using different spacers that vary in length, chemical nature, and attachment position with the dye. This led to an efficient energy and/or electron transfer in all dyad systems leading to an enhanced QE and photostability for at least one year. To demonstrate the potential application of the functionalized SQDs for bioimaging applications, they were examined for fluorescent imaging of HeLa, HEK293, and U2OS cells

Charge and energy transfer in porphyrin dyads and oligomers

Résumé : Le travail de recherche présenté dans ce mémoire fut inspiré par le processus de la photosynthèse qui se produit chez les plantes. Au cours de ce processus l’énergie solaire est convertie en énergie chimique via différentes étapes de transferts d’électrons et d’énergie. En maîtrisant bien ces concepts, de nombreuses applications, telles que les cellules photovoltaïques ou les DEL (Diodes électro-luminescentes) peuvent être améliorées. Pour se faire, il est important d’optimiser les propriétés des matériaux existants (oligomères, polymères, etc…) en préparant des systèmes conjugués plus efficaces, mais aussi de pleinement comprendre les processus qui s’y produisent (processus de transferts d’électrons et d’énergie photo-induist). La série d’oligomères et de polymères présentée dans ce mémoire le sont pour leurs applications dans des systèmes photoniques. Dans cette optique, ce mémoire a été divisé en cinq grands chapitres. Le premier présente les principes théoriques de la photophysique. Le second présente le suivi du transfert d’énergie T[indice inférieur 1] dans les états triplets, T[indice inférieur 1], une dyade constituée de la tétraphénylporphyrine de zinc(II), [ZnTPP], et de la bis(phénylpyridinato)(bipyridine) d’iridium(III), [Ir], chromophores liés avec un pont trans-diéthynylbis(phosphine)-platine(II). Malgré que cette dyade soit entièrement conjuguée et qu’elle soit constituée d’un donneur ([ZnTPP]) et d’un accepteur ([Ir]), aucun transfert d’énergie T[indice inférieur 1] [Ir] → S[indice inférieur 1]/T[indice inférieur 1] [ZnTTP] n’a été observé. Ce résultat fut attribué à l’absence de recouvrement des orbitales moléculaires entre la HSOMO(donneur*) et la HSOMO(accepteur), LSOMO(accepteur) and LSOMO (donneur*) (mécanisme de Dexter). Ainsi, l’échange d’électrons est impossible. Ce chapitre suggère que l’équation de Dexter, k[indice inférieur Dexter] = KJexp(-2r[indice inférieur DA]/L) ne reste qu’une approximation. Ce travail a été publié dans ChemComm (2013, 49, 5544-5546). Le troisième chapitre présente le transfert d’énergie singulet beaucoup lent qu’attendu se produisant dans une dyade constituée d’une porphyrine de zinc(II) avec une porphyrine base libre liées par un pont palladium(II) (trans-PdI[indice inférieur 2]). Sachant que cette dyade est entièrement conjuguée et que la distance entre les deux centres de masse des porphyrines est relativement courte, ce système aurait dû présenter un transfert d’énergie très rapide, d’après la théorie de Förster. Dans ce cas, ce comportement a été expliqué par le faible recouvrement des orbitales frontières (OM) du donneur et de l’accepteur. Ce travail a été accepté le 2014-05-26 dans Chemistry – A European Journal (chem.201403146). Le quatrième chapitre rapporte une étude du transfert d’énergie ultra-rapide (650 fs) entre des états singulets dans une dyade composé d’une porphyrine de zinc(II) (le donneur) et une porphyrine base libre (l’accepteur) liées à l’aide d’un pont de palladium ([beta],[beta]--trans-Pd(NH)[indice inférieur 2](CO)[indice inférieur 2]). Ces résultats ont été attribués à la présence d’un couplage fort entre les OM du donneur et de l’accepteur et de la très faible contribution (atomique) du Pd(II) vers ces OM. Cette dyade montre la plus rapide constante de transfert d’énergie k[indice inférieur ET] que nous connaissons pour des dyades similaires contentant un fragment métallique. Les résultats du troisième et quatrième chapitre montrent que la théorie de Förster tel quel ne suffit pas pour prédire les vitesses de transferts d’énergie dans certains systèmes : d’autres facteurs doivent être pris en compte. Ce travail a été soumis dans JACS ( ja-2014-061774, 19-6-2014). Dans le cinquième chapitre de ce mémoire, la synthèse du bis(-[alpha]-(amino(4-éthynylbenzene (triméthylsilane)(R))))bis(4-éthynylbenzene-(triméthylsilane))quinone diimine (R= H, Boc) comme modèle pour des polymères conjugués et non-conjugués contenant le colorant porphyrine a été proposée. Le corps du composé désiré (tétrakis(4-éthynlyphenyl)quinone-1,4-diimine-2,5-diamine) a montré un transfert de charge partant des groupes terminaux riches en électrons une la benzoquinone centrale plus pauvre. La nature de l’émission fut observée uniquement à 77K pour le cas où R = H et fut attribuée à de la fluorescence. À température ambiante, l’intensité était trop faible pour être observée. Dans le cas où R = Boc, aucune emission n’a été détectée. Malheureusement, le composé espéré ne fut pas obtenu, le procédé de synthèse employé engendra uniquement la forme réduite. Cette forme fut malgré tous analysé, et ne présenta pas de transfert de charge ni de communication entre les différents chromophores. Ceci a été expliqué simplement par le fait que la conjugaison est brisée quand ce composé est sous sa forme réduite. Ce travail sera soumis au Journal of Inorganic and Organometallic Polymers and Materials. // Abstract : The research work presented in this master thesis is inspired by the photosynthetic process occurring in plants where solar energy is converted into chemical energy via several energy and electron transfer processes. In the light of these concepts, several applications such as solar cells and light emitting diodes can be improved. To do so, we need to optimize the properties of polyads, oligomers and polymers to device more efficient conjugated materials as well as developing a full understanding of the photo-induced energy and electron transfer processes that occur. Several organometallic oligomers and polymers are presented in this thesis due to their potential photonic applications. In this respect, this master thesis has five chapters. The first one introduces some theoritical principles of photophysics. The second one presents the monitoring of triplet state (T[subscript 1]) energy transfer in a dyad that consists of zinc(II)tetraphenylporphyrin, [ZnTPP], and bis(phenylpyridinato)-(bipyridine)iridium(III), [Ir], chromophores linked by a platinum(II) containing bridge. Despite the conjugation in this dyad and the presence of the [ZnTPP] energy donor and the [Ir] energy acceptor species, no T[subscript 1] [Ir] → S[subscript 1]/T[subscript 1] [ZnTTP] energy transfer occurs. This result was explained by the absence of MO overlap between HSOMO(donor*) and HSOMO(acceptor), LSOMO(donor*) and LSOMO(acceptor) , and hence no efficient double electron transfer exchange (i.e. Dexter mechanism) is likely to occur. This chapter suggested that Dexter formulation, k[subscript Dexter] = KJexp(-2r[subscript DA]/L), appears as an approximation. This work has been published in ChemComm (2013, 49, 5544-5546). The third chapter shows an unexpected slow singlet energy transfer in a dyad built upon a zinc(II)porphyrin and the corresponding free base chromophores linked by a palladium(II)- containing bridge (trans-PdI[subscript 2]), despite the presence of conjugation and the relative short center-to-center distance. This behavior was explained by two factors, the first is the lack of large molecular orbitals (MOs) overlaps between the frontier MOs of the donor and acceptor, and thus preventing a double electron exchange to occur through the trans-PdI[subscript 2] bridge. The second factor affected the energy transfer is the electronic shielding induced by the presence of this same linker, namely the electron rich iodides, preventing the two VI chromophores to fully interact via their transition dipoles. This work has been accepted on 2014-05-26 in Chemistry-A European Journal (chem.201403146). The fourth chapter reports an ultrafast singlet energy transfer (650 fs) in a dyad composed of a zinc(II)porphyrin (donor) and a free base porphyrin (acceptor) [beta],[beta]-linked via trans- Pd(NH)[subscript2](C=O)[subscript 2]. These results were explained by the presence of strong MO couplings of the donor and acceptor and the very weak atomic contribution of the Pd(II) atom to this MO. This dyad shows the fastest energy transfer rate k[subscript ET] among other similar dyad systems incorporating a bridge either in the form of a metal fragment or carbon-based. The results of these third and fourth chapters showed that the Förster mechanism is not enough to account for the energy transfer in some systems and other factors affect that transfer. This work has been submitted in JACS ( ja-2014-061774, 19-6-2014). In chapter 5, the synthesis of bis-[alpha]-(amino(4-ethynylbenzene (trimethylsilane)(R))bis(4- ethynylbenzene-(trimethylsilane))quinone diimine (R = H, Boc) as a model for conjugated and unconjugated porphyrin dye polymers was proposed. The central core of the desired compound, tetrakis(4-ethynlypenyl)quinone-1,4-diimine-2,5-diamine, provided evidence for a charge transfer interaction from the electron richer terminal groups to be more electron poorer benzoquinone ring. The nature of the emission of the core compound was found to be fluorescence at 77K for the case R = H but was too weak to be observed at 298K. No emission was detected for the case R = Boc. Unfortunately, the synthetic route of the desired compound gave the reduced form. The analyses of the reduced compound showed the complete absence of the charge transfer or any communication between the different chromophores due to the broken conjugation between the porphyrin units in the reduced product. This work will be submitted to Journal of Inorganic and Organometallic Polymers and Materials

Evaluation and Analysis of Cavitation Phenomenon in Rosieres Power Plant, Sudan, 2011-2012

Cavitation is one of the serious problems in hydraulic turbines negatively affects their efficiency and may cause damages. Cavitation is a phenomenon which occurs as a pitting of metallic surfaces of turbine parts because of the formation of cavities. In this paper, cavitation in Kaplan turbine unit 2 in Rosieres power plant was studied and analyzed during flood, water restriction and blackout periods. The general features of cavitation were described and cavitation variables were determined in the plant. Cavitation indexes and critical cavitation factors were calculated and compared during these three periods. The results showed that: the turbines were operated within cavitation limit during these periods. Cavitation index was found to be higher in water restriction, while minimum power and drop of pressure, which also increase the possibility of cavities were found in flood and blackout

Evaluation of Laparoscopic Sphincter Saving Surgery in Management of Rectal Cancer

Background: Sphincter-saving surgery for rectal carcinoma (RC) has been classically performed by open surgery. Laparoscopic restorative proctectomy (LRP) has been evolved for the same purpose, but its benefits are controversial representing an enigma in the choice of management of RC.Objective: The aim of this study was to evaluate the feasibility, adequacy, safety, short- and long-term outcomes of LRP.Patients and methods: This was a prospective observational study included 35 patients suffering from middle and distal third RC admitted electively to Sohag University Hospital and Colorectal Unit in Ain Shams University. Patients were evaluated and analysed regarding efficacy of LRP, length of stay and different risk factors for post-operative complications.Results: Regarding operative outcomes the mean operative time was 189 minutes, and mean operative blood loss was 95.4 mL, while operative complications happened in 8.5%. Post-operatively, complications happened in 22.9%. The mean post-operative hospital stay was 4.2 ± 1.4 days. Higher American Society of Anesthesiologists (ASA) risk scoring and advanced pathological stage proved to be independent risk factors responsible for complications. During follow-up, local recurrence was evident in 5.7% and distant recurrence developed in further 5.7%. Disease-free survival rate was 80.02 %, and overall survival rate was 91.3% for stage II and 83.3% for stage III. Conclusion: LRP can be done safely reflecting adequacy of the procedure with a comparable complication rate and long-term outcomes to conventional surgery, which makes it a good alternative to conventional technique

Tuning the optical properties of silicon quantum dots via surface functionalization with conjugated aromatic fluorophores

The authors acknowledge Karen Nygard at UWO Biotron for assistance with confocal microscopy. This work was financially supported by NSERC Canada Discovery (Charpentier).Silicon Quantum Dots (SQDs) have recently attracted great interest due to their excellent optical properties, low cytotoxicity, and ease of surface modification. The size of SQDs and type of ligand on their surface has a great influence on their optical properties which is still poorly understood. Here we report the synthesis and spectroscopic studies of three families of unreported SQDs functionalized by covalently linking to the aromatic fluorophores, 9-vinylphenanthrene, 1-vinylpyrene, and 3-vinylperylene. The results showed that the prepared functionalized SQDs had a highly-controlled diameter by HR-TEM, ranging from 1.7–2.1 nm. The photophysical measurements of the assemblies provided clear evidence for efficient energy transfer from the fluorophore to the SQD core. Fӧrster energy transfer is the likely mechanism in these assemblies. As a result of the photogenerated energy transfer process, the emission color of the SQD core could be efficiently tuned and its emission quantum efficiency enhanced. To demonstrate the potential application of the synthesized SQDs for bioimaging of cancer cells, the water-soluble perylene- and pyrene-capped SQDs were examined for fluorescent imaging of HeLa cells. The SQDs were shown to be of low cytotoxicity.Publisher PDFPeer reviewe

Distribution and diversity of fish species along the Sudanese Red Sea coast based on three combined trap and gillnet surveys

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Electrical power output prediction of combined cycle power plants using a recurrent neural network optimized by waterwheel plant algorithm

It is difficult to analyze and anticipate the power output of Combined Cycle Power Plants (CCPPs) when considering operational thermal variables such as ambient pressure, vacuum, relative humidity, and temperature. Our data visualization study shows strong non-linearity in the experimental data. We observe that CCPP energy production increases linearly with temperature but not pressure. We offer the Waterwheel Plant Algorithm (WWPA), a unique metaheuristic optimization method, to fine-tune Recurrent Neural Network hyperparameters to improve prediction accuracy. A robust mathematical model for energy production prediction is built and validated using anticipated and experimental data residuals. The residuals’ uniformity above and below the regression line suggests acceptable prediction errors. Our mathematical model has an R-squared value of 0.935 and 0.999 during training and testing, demonstrating its outstanding predictive accuracy. This research provides an accurate way to forecast CCPP energy output, which could improve operational efficiency and resource utilization in these power plants

Forecasting wind power based on an improved al-Biruni Earth radius metaheuristic optimization algorithm

Wind power forecasting is pivotal in optimizing renewable energy generation and grid stability. This paper presents a groundbreaking optimization algorithm to enhance wind power forecasting through an improved al-Biruni Earth radius (BER) metaheuristic optimization algorithm. The BER algorithm, based on stochastic fractal search (SFS) principles, has been refined and optimized to achieve superior accuracy in wind power prediction. The proposed algorithm is denoted by BERSFS and is used in an ensemble model’s feature selection and optimization to boost prediction accuracy. In the experiments, the first scenario covers the proposed binary BERSFS algorithm’s feature selection capabilities for the dataset under test, while the second scenario demonstrates the algorithm’s regression capabilities. The BERSFS algorithm is investigated and compared to state-of-the-art algorithms of BER, SFS, particle swarm optimization, gray wolf optimizer, and whale optimization algorithm. The proposed optimizing ensemble BERSFS-based model is also compared to the basic models of long short-term memory, bidirectional long short-term memory, gated recurrent unit, and the k-nearest neighbor ensemble model. The statistical investigation utilized Wilcoxon’s rank-sum and analysis of variance tests to investigate the robustness of the created BERSFS-based model. The achieved results and analysis confirm the effectiveness and superiority of the proposed approach in wind power forecasting

A novel voting classifier for electric vehicles population at different locations using Al-Biruni earth radius optimization algorithm

The rising popularity of electric vehicles (EVs) can be attributed to their positive impact on the environment and their ability to lower operational expenses. Nevertheless, the task of determining the most suitable EV types for a specific site continues to pose difficulties, mostly due to the wide range of consumer preferences and the inherent limits of EVs. This study introduces a new voting classifier model that incorporates the Al-Biruni earth radius optimization algorithm, which is derived from the stochastic fractal search. The model aims to predict the optimal EV type for a given location by considering factors such as user preferences, availability of charging infrastructure, and distance to the destination. The proposed classification methodology entails the utilization of ensemble learning, which can be subdivided into two distinct stages: pre-classification and classification. During the initial stage of classification, the process of data preprocessing involves converting unprocessed data into a refined, systematic, and well-arranged format that is appropriate for subsequent analysis or modeling. During the classification phase, a majority vote ensemble learning method is utilized to categorize unlabeled data properly and efficiently. This method consists of three independent classifiers. The efficacy and efficiency of the suggested method are showcased through simulation experiments. The results indicate that the collaborative classification method performs very well and consistently in classifying EV populations. In comparison to similar classification approaches, the suggested method demonstrates improved performance in terms of assessment metrics such as accuracy, sensitivity, specificity, and F-score. The improvements observed in these metrics are 91.22%, 94.34%, 89.5%, and 88.5%, respectively. These results highlight the overall effectiveness of the proposed method. Hence, the suggested approach is seen more favorable for implementing the voting classifier in the context of the EV population across different geographical areas