12 research outputs found

    MOLECULAR DESIGN AND SYNTHESIS OF DYES FOR DYE-SENSITIZED SOLAR CELLS (DSSCS)

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    ABSTRACT Background Solar energy plays a critical role in meeting the global energy challenge and represents one of the most promising energy sources for the future of the planet. Solar or photovoltaic cells are currently a hot topic on the market, these are devices that convert the energy of sunlight directly into electricity trough the photovoltaic effect. Strong and competitive research is currently devoted to lower the material costs of solar cells, and to increase their energy conversion efficiency. Up to now, commercially available photovoltaic technologies are based on inorganic materials, mainly crystalline silicon (first generation) and other semiconductors, such as gallium arsenide, indium phosphide and cadmium telluride (second generation In addition to high costs, also in terms of energy consuming, in fabrication processes, several of those materials are toxic and have low natural abundance. Therefore, in the last two decades the research focused on the development of a third generation of solar cells based on hybrid or organic materials, that offers a number of advantages, such as: high molar extinction coefficients, versatility of the chemical design for modulating the electronic properties, easy processability as well as low manufacturing costs. Although the efficiencies of organic-based photovoltaic cells (\uf07e 8%) are still at the moment a long way behind those obtained with purely inorganic based photovoltaic technologies ( \uf07e20%), the power conversion efficiency of organic solar cells have been significantly improved and there are expectations for more important results. Among the third generation of solar cells, the Dye-Sensitized Solar Cells (DSSC), also called Gr\ue4tzel cells, have emerged as very promising candidates for low-cost alternative to conventional semiconductor photovoltaic devices. A DSSC cell scheme is shown in Figure 1. The cell components are: a mesoporous film of TiO2 (anode), a dye-sensitizer, an electrolyte, an electrochemical mediator and a cathode. The photovoltaic process in this cells can be resumed as follows: the dye-sensitizer (S), linked to semiconducting TiO2 surface (usually through a carboxylic group), absorbs a photon passing to the excited state S*, which transfers an electron to the conduction band of TiO2. The oxidized S+ thus obtained, is reduced by a redox mediator, generally I- from the couple I-/I3- dissolved in the electrolyte. The electron injected in TiO2 through the external circuit arrives to the cathode, where the reduction of I3- regenerates the iodide, closing the circuit. (Figure 1). Figure 1 The DSSC technology separates two requirements as: i) the charge generation, done at the semiconductor-dye interface and ii) the charge transport, done by the semiconductor and the electrolyte. Consequently, carrier transport properties can be improved by optimizing the semiconductor and electrolyte composition, while the spectral properties and thus charge generation can be improved by modifying the dye structure, that can be tailored in many ways by organic chemistry contribution. Many kinds of dyes have been studied for DSSCs application and in principle they could be divided in two classes (Figure 2): 1. metal complexes (N719, Zn-porphyrine e.g YD2-o-C8) , , 2. metal-free system Donor-Spacer-Acceptor (TA-St-CA) Figure 2 Up to now the best efficiencies (~11%) have been reached using ruthenium complexes, thanks to their large absorption range from visible to near infrared (NIR), and their capability to easily inject electrons in the conducting band of the semiconductor. The metal based chromophores still have several disadvantages such as not very high molar extinction coefficient and the presence of the expensive metal, such as ruthenium, which involves complicated synthesis and hard purification steps. On the contrary, metal-free dyes are simple and cheap to prepare and it is possible to easily modulate their photo- and electrochemical properties varying the functionalization, but very high efficiencies have not been achieved yet. The obtainment of new and more efficient dyes is therefore object of competitive international researches. Within this context, the present Ph.D. research project has focused on the synthesis of new metal-complexes and metal-free organic dyes characterized by a Donor-Spacer-Acceptor (D-\u3c0-A) structure, (Figure 3) in which the novelty is represented by the presence of benzo-condensed thiophene units as \u3c0 bridge spacer. Figure 3 Aim of the work In such chromophores the \u3c0 spacer plays a fundamental role, as it is responsible for the electronic communication between acceptor and donor moiety and for the extension of the conjugation that lead to wider and red-shifted absorption spectra. To date a number of new \u3c0-conjugated aromatic and heteroaromatic systems have been investigated and among these, thiophene or thienothiophene \u3c0-bridges have been reported to give remarkable efficiency. Benzodithiophenes systems BDT and BDT1 (Figure 4) attracted our attention because their rigid, \u3c0-conjugated, condensed-polycyclic structure , leads to unique electronic properties such as conductivity, high field effect mobility and tunable stacking in the solid state; rigid structures hamper the roto- vibrational modes responsible for the deactivation of the excited states in functional materials. Figure 4 In this Ph. D. work we investigated synthesis of suitably functionalized BDT and BDT1 derivatives as well as their use for the construction of two classes of dyes: 1) Zn-porphyrin based dyes (in collaboration with the research group of Prof. Pizzotti and Prof. Ugo) and 2) metal-free dyes and, Zn-porphyrin based dyes In addition the design of the new dyes have been oriented by preliminary theoretical calculations, done in collaboration with Dr. Filippo De Angelis of CNR-ISTM in Perugia, that allowed to gain insight into the molecular, ground and excited state electronic structure of the new chromophores. 1. Synthesis of new benzodithiophene containing Zn-porphyrins Metal porphyrins, characterised by very strong absorption bands around 450 nm (Soret band) and 600-700 nm (Q band) are potentially interesting as dyes for DSSC. For example, some push-pull type porphyrins bearing a carboxylic acid moiety as an anchoring group, have disclosed a remarkably high power conversion efficiency (6-7%), therefore in the recent years some research efforts have been devoted to the design, synthesis and application of new porphyrin-based chromophores for DSSC. , , The unique feature of these sensitizers is that the porphyrin chromophore itself constitutes the \u3c0-bridge of the D-\u3c0-A structure and with the aim of increasing the conjugation of the system, some new Zn porphyrins, containing the BDT1 unit (Figure 5), have been designed in our group. These porphyrin molecules are differently functionalized in 5,15 and 10,20 meso positions. In positions 5 and 15, aromatic rings bearing bulky groups are needed to avoid aggregation on the semiconductor surface, that drastically Figure 5 reduce the dye light-harvesting by a filtering effect. In 10,20 meso positions the structure presents two \u3c0-delocalized aromatic systems with opposite (electron-withdrawing or electron-donating) properties, in order to realize a push-pull system in which is possible to modulate the position and the intensity of the Q band and to favor the electron flow. The most promising structures were selected on the basis of preliminary theoretical calculations done by Dr. De Angelis and synthesized in collaboration with Prof. Ugo and Prof. Pizzotti\u2019s research group. The novel Zn-porphyrin system 1 (Figure 6) was first synthesized, whose structure is characterized by the presence of BDT1 system in the acceptor part of the molecule. The suitable 2,6 di-functionalized BDT1 derivative was prepared and then linked to the porphyrin core. Figure 6 The resulting new Zn-porphyrin 1 was completely characterized from the analytical and photophysical point of view and used in preliminary tests as dye in Gr\ue4tzel solar cells, giving an efficiency of 0.6%. Slightly optimization of the cell structure and in the composition of the electrolyte led to an increased efficiency of 2,54%. This result, although unsatisfactory, served as a starting point for the set-up of a number of synthetic protocols and for designing more targeted substitution and variation in the molecule structure. This part of the work is currently under progress. 2. Synthesis of benzodithiophene containing metal-free dye As already mentioned, the general structure of a metal-free dye, reported in Figure 3, presents a donor and an acceptor unit linked by a \u3c0-conjugate system. The most efficient structures reported in the literature contain triarylamines as donor unit, because of the prominent electron-donating ability and hole-transport of such molecules. Within this topic we designed novel metal-free triarylamine-containing organic dyes endowed with the innovative spacers BDT1 and its isomer BDT. Also in this case the design of the new compounds was oriented by preliminary TD-DFT calculations made by Dr. De Angelis, on two parent BDT1-containing structures 15 and 16, which differ from each other by the presence of a triple or a double bond. (Figure 7) With the aim to investigate the structure-performance relationship of the dyes in the cell, we designed a small library of structures, changing the BDT-bridge (17), the acceptor group (18) or the donor (19, 20) with respect of the model compound 16. (Figure 7). This allowed us to investigate the potentiality of BDT and BDT1 in the dyes in combination with double or triple bond in order to elongate the conjugation, and to obtain band gap reduction and enlarge the absorption spectra. In particular, the presence of the triple bond should ensures more planarity and therefore conjugation and avoids energy losses due to photoisomerization. The series of synthesized dyes are reported in figure 7. Figure 7 Almost all the dyes synthesized have also been characterized from a photophysical as well as electrochemical point of view, with the aim of identifying, among them, the most interesting and promising compounds for application in solar cells and try to clarify the relationship between the chemical structure and photovoltaic performances. Preliminary test in DSCs have been carried out for some of the dyes and among these dye 16 has emerged as the most promising one leading to an efficiency in liquid state cell of 5.11% and confirming the potential of BDT1 \u3c0-spacer for application in DSSCs. The cell efficiency found for 16, which is however still under optimization, allows us to say that this dye ranks among the promising dyes to date reported in literature. In addition, it must be pointed out that dye 16 seems to possess most of the essential chromophore characteristics required for obtaining high-performance DSSCs. The systematic study developed during the present Ph.D. thesis will be very useful for future improvement of the synthesized structures and their photovoltaic performances in DSSCs

    NANOSTRUCTURED MATERIALS FOR ENVIRONMENTAL AND ENERGY-RELATED APPLICATIONS

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    The world is facing an era of global environmental pollution, as a result of the tremendous population growth and the consequent massive fossil fuel-based energy consumption. A significant exploitation of renewable energies is needed to guarantee quality of human life and allow further sustainable growth, but this may take decades to happen. In order to mitigate the negative effect of human activities on the environment in the short- and mid-term, the development of more efficient technologies for emissions abatement and for renewable fuels production is imperative. Heterogeneous catalysis and photocatalysis are two key pillars of a multi-approach strategy to solve these issues. During the last century, catalysts were explored by changing the formulation of multi-component systems in order to find the best performing material for a certain reaction. Since the late 90's, a new approach to catalytic systems improvement emerged: nano-catalysis. Exploiting the tools of nanotechnology, tailored nanostructured materials can now be produced, which show different properties in comparison to their bulky counterparts, often resulting in better catalytic performances. Furthermore, combining the elements of the periodic table in nano-alloys allows to expand the possibility of catalyst generation. Consistently with these approaches, the main focus of this thesis is the synthesis and characterization of well-defined nanostructured and hierarchical materials for environmental and energy-related applications, such as emissions control, biofuels synthesis and photocatalytic H2 production. We show that structural control at the nanoscale is a great instrument for understanding reaction pathways, for studying the nature of catalytic active sites, and for synthesizing more selective, active and stable catalysts. Two synthetic strategies were followed to acquire nanostructural control: a self-assembly method was employed to prepare hierarchical materials starting from functional nanoparticles, and advanced solvothermal methods were used to prepare monodisperse nanocrystals having controlled size and composition. State-of-the-art hierarchical Pd-based catalysts embedded by metal oxide promoters were tested for methane catalytic oxidation in the presence of poisoning compounds typically found in real applications. Detailed surface studies allowed to propose deactivation mechanisms and strategies to improve catalysts resistance to deactivation. Well-controlled nanostructured Pt-based alloys and Ni-Cu alloys showed improved activity, stability and selectivity for hydrodeoxygenation reactions of biomass-derived feedstocks to produce biofuels. The control of nanostructure was pivotal to understand the reason for such enhanced performances. Finally, dye-sensitized photocatalysts were investigated in H2 photocatalytic production under visible light, and state-of-the-art stability and activities were demonstrated. All these findings greatly contributed to the development of catalytic materials for energy-related applications

    Compositional Characterization of Organo-Lead tri-Halide Perovskite Solar Cells

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    Perovskite photovoltaics is one of the fastest growing research fields in materials science. Apart from photovoltaics, a wide range of energy-related research fields have gained substan-tial new momentum owing to the fantastic optoelectronic properties of hybrid lead halide per-ovskites. Starting with solar cells showing a mere 3% power conversion efficiency in 2009, researchers have been able to increase this value to over 22% in 2017, comparable to the best monocrystalline silicon solar cells. These improvements are chiefly due to the compositional tuning and mixing of the ABX3 perovskite structure. However, this strategy increases not only the efficiency but also in the same time the complexity of the perovskite formulation. Differ-ent phases, from the nano- to macroscale, can potentially form. In order to rationalize the effi-ciency progress, one needs to understand and characterize the complex perovskite composi-tion and crystal structure in great detail. The main focus of this thesis lies in the in-depth compositional and phase analysis of perovskite thin films as well as full perovskite solar cells, trying to rationalize the consequences of A cation and X anion tuning and mixing. In the first part, it is shown that fabricating solar cells from a non-stoichiometric perovskite precursor composition, namely one with PbI2 excess, leads to increased grain size, enhanced cristallinity, reduced recombination as well as an improved TiO2/perovskite interface. As op-posed to lead iodide phases resulting from film degradation, which is hampering device per-formance, unreacted excess PbI2 phases originating from an excess of PbI2 in the precursor solution are very beneficial for the final solar cell efficiency, reproducibility and stability. The next scientific challenge adressed in this thesis is related to the nano- and microscale composition of the record-breaking mixed cation/mixed anion perovskite composition. Mac-roscale investigations have previously suggested that this formulation results in a single ho-mogenous phase. However, using nanoscale elemental and charge carrier distribution mapping as well as microscale structural and optical film analysis, it is here found that in high efficient solar cells partial phase segregation does take place at the micro- and nanoscale. Moreover, it is shown that mixed cation/anion formulations allow the formation of never re-ported 3D hexagonal lead halide perovskite polytypes, namely 4H and 6H. These polytypes are shown to play a key role during the crystallization process, which is also revealed for the first time here. Indeed, mixed cation/mixed anion perovskite films are fabricated via the crys-tallization sequence 2Hï 4Hï 6Hï 3R(3C). It is demonstrated that the complex crystalliza-tion via these defect-prone hexagonal intermediates can be by-passed by the incorporaton of low amounts of Cs+ cations into the structure. This can explain the improved stability as well as the increased power conversion efficiency and device reproducibility. It gives for the first time a rational explanation as to why the halide perovskite community rapidly adopted the incorporation of Cs+ in mixed perovskites. The last results presented in this thesis are related to the hole-transporting materials (HTM) used in perovskite solar cells. It is shown that carbazole-based small molecule HTMs are a cheap and efficient alternative to the much costlier commercial spiro-OMeTAD

    Hybrid Quantum Dot-Organic Solar Cells by Solution Processing

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    Department of Energy EngineeringEnvironmental cleaned renewable energy resources such as solar energy have gained significant attention because of the continual enhancement in worldwide energy requirement. A variety of technologies have been developed to make the best use of solar energy. For instance, solar cells based inorganic materials such as silicon wafer can convert solar energy directly to an electricity energy, however inorganic materials are expensive to manufacture, and thus unattractive for general use. Therefore, many researchers have focused on the low cost and easy processing strategies are underway to confirm the materials and solar cells device architectures that are inexpensive efficient compared to inorganic solar cells such as silicon solar cells. Recently, solution processing thin film solar cells is highlighted and many researchers working on this field. Therefore, conjugated polymer based on the solar cells is rapidly growth and achieved power conversion efficiency (PCE) over 10% in single junction. And quantum dot solar cells (QDSCs) reported over 8% PCE at short period time. Here, I present positive effect on combination in the organic and quantum dot (QD) for solar cells application with all solution processing. First, The effect of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) as a buffer layer was investigated in PSCs. Four different types of PEDOT:PSS were used: PH, PH500 and their DMSO-doped counterparts. The efficiency of PSCs was independent of the electric conductivity of the buffer layer as a bulk property. Second, the effect of ionic liquid molecules (ILMs) in QD-organic hybrid solar cells. The insertion of a ILMs layer between PbS QD and Phenyl-C61-butyric acid methyl ester (PCBM) can shift the band edge of the PCBM closer to the vacuum level of PbS. Owing to this new architecture, improvements in device performance were achieved. Third, new technique for preparing inverted colloidal QDSCs using layer-by-layer processed PbS QD and a ZnO layer formed via the solution-phase decomposition of diethyl zinc directly on the PbS film. The inverted QDSCs enhanced in device characteristics stem from constructive optical interference in the absorbing PbS QD layer, as well as outstanding diode characteristics arising from a superior PbS/ZnO junction achieved substantial improvements in short-circuit current, open circuit voltage, fill factor and PCE relative to a control device. Fourth, new types of architecture of hybrid QD-organic solar cells (by introducing PbS QD layer as performing role of photo sensitized layer to achieve high Jsc and PCE using NIR region up to 1100 nm from PbS QD light absorbed.ope

    Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

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    Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photo-activatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review

    Développement et caractérisation de dérivés dipyrrométhène pour des applications dans le domaine du photovoltaïque

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    Ce projet de recherche mené en collaboration industrielle avec St-Jean Photochimie Inc. / PCAS Canada vise le développement et la caractérisation de dérivés dipyrrométhène pour des applications dans le domaine du photovoltaïque. La quête du récoltage des photons se situant dans le proche-infrarouge a été au centre des modifications structurales explorées afin d’augmenter l’efficacité de conversion des cellules solaires de type organique et à pigments photosensibles. Trois familles de composés intégrant le motif dipyrrométhène ont été synthétisées et caractérisées du point de vue spectroscopique, électrochimique, structural ainsi que par modélisation moléculaire afin d’établir des relations structures-propriétés. La première famille comporte six azadipyrrométhènes au potentiel de coordination tétradentate sur des centres métalliques. Le développement d’une nouvelle voie synthétique asymétrique combinée à l’utilisation d’une voie symétrique classique ont permis d’obtenir l’ensemble des combinaisons de substituants possibles sur les aryles proximaux incluant les noyaux 2-hydroxyphényle, 2-méthoxyphényle et 2- pyridyle. La modulation du maximum d’absorption dans le rouge a pu être faite entre 598 et 619 nm. De même, la présence de groupements méthoxyle ou hydroxyle augmente l’absorption dans le violet (~410 nm) tel que démontré par modélisation. La caractérisation électrochimique a montré que les dérivés tétradentates étaient en général moins stables aux processus redox que leur contre-parti bidentate. La deuxième famille comporte dix dérivés BODIPY fusionnés de façon asymétrique en position [b]. L’aryle proximal a été modifié de façon systématique afin de mieux comprendre l’impact des substituents riches en électron et de la fusion de cycles aromatiques. De plus, ces dérivés ont été mis en relation avec une vaste série de composés analogues. Les résultats empiriques ont montré que les propriétés optoélectroniques de la plateforme sont régies par le degré de communication électronique entre l’aryle proximal, le pyrrole sur lequel il est attaché et le noyau indolique adjacent à ce dernier. Les maximums d’absorption dans le rouge sont modulables entre 547 et 628 nm et la fluorescence des composés se situe dans le proche- infrarouge. L’un des composé s’est révélé souhaitable pour une utilisation en photovoltaïque ainsi qu’à titre de sonde à pH. La troisième famille comporte cinq complexes neutres de RuII basés sur des polypyridines et portant un ligand azadipyrrométhène cyclométalé. Les composés ont montré une forte absorption de photons dans la région de 600 à 800 nm (rouge à proche- infrarouge) et qui a pu être étendue au-delà de 1100 nm dans le cas des dérivés portant un ligand terpyridine. L’analyse des propriétés optoélectroniques de façon empirique et théorique a montré un impact significatif de la cyclométalation et ouvert la voie pour leur étude en tant que photosensibilisateurs en OPV et en DSSC. La capacité d’un des complexes à photo-injecter un électron dans la bande de conduction du semi-conducteur TiO2 a été démontré en collaboration avec le groupe du Pr Gerald J. Meyer à University of North Carolina at Chapel Hill, premier pas vers une utilisation dans les cellules solaires à pigments photosensibles. La stabilité des complexes en solution s’est toutefois avérée problématique et des pistes de solutions sont suggérées basées sur les connaissances acquises dans le cadre de cette thèse.This research project carried out in industrial collaboration with Saint-Jean Photochemicals Inc. / PCAS Canada aims at the development and characterization of dipyrromethene derivatives for photovoltaic applications. The quest for harvesting near- infrared photons was the central focus and various structural modifications were explored to improve the power conversion efficiency of organic and dye-sensitized solar cells (OPV and DSSC, respectively). Three families of chromophores which embedded a dipyrromethene motif were synthesized and characterized through spectroscopy, electrochemistry, X-ray diffraction and computationnal modelization in order to establish their structure-properties relationship. The first family includes six azadipyrromethenes with potential for tetradentate coordination on metallic centers. The development of a new asymmetric synthetic route together with the classical symmetric one allowed access to all possible combinations of derivatives including 2-hydroxyphenyl, 2-methoxyphenyl and 2-pyridyl substituents in the proximal position of the dipyrromethene. Modulation of the absorption maxima in the red ranged between 598 and 619 nm. Also, having methoxy or hydroxy substituents provided an increase of the violet absorption (~410 nm) as established by modelization. Electrochemical characterization showed that the tetradentate azadipyrromethenes were generally less stable towards redox processes as compared to their bidentate counter- parts. The second family includes ten asymmetric benzo[b]-fused BODIPYs where the proximal aryl was systematically modified in order to assess the impact of electron-rich substituents and fused aromatic cycles. The derivatives were further compared to a wide series of related BODIPYs. Empirical results showed the optoelectronic properties are dictated by the extend of electronic communication between the proximal aryl, the pyrrol to which it is attached and the adjacent indolic moiety. Absorption maxima in the red were modulated between 547 nm and 628 nm and the fluorescence was in the near-infrared. One compound proved to be a potential candidate for photovoltaic and pH probe applications. The third family includes five neutral RuII polypyridine complexes bearing a cyclometalated azadipyrromethene ligand. The compounds exhibit strong light absorption in the 600 – 800 nm range (red to near-infrared) that tails beyond 1100 nm in the terpyridine-based adducts. Analysis of the optoelectronic properties showed a significant impact of this novel cyclometalation strategy for dipyrromethene derivatives and paved the way for further incorporation of the resulting complexes as photosensitizers in OPV and DSSC. In collaboration with the group of Pr Gerald J. Meyer at the University of North Carolina at Chapel Hill, the capacity of one compound to photo-inject its electron into the conduction band of the TiO2 semiconductor was established, a first step towards their use in dye-sensitized solar cells. The structural instability in solution of the complexes hindered their full potential for photovoltaic applications and suggestions to improve them are proposed based on the knowledge acquired in the course of this thesis

    Luminescent EuIII complexes based on phenanthro-imidazole ligands for white LEDs/OLEDs and temperature sensors: Combined experimental and theoretical investigations

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    The present theis works deals with molecular designing and synthesis of novel class bipolar or ancillary ligand for europium complexes and explore the possibility of using the same in white LEDs, temperature sensor and OLED applications In chapter 1, a general overview of the development of new-generation optical lanthanide based complexes - introduction, literature survey of recent trends and brief objectives of the thesis was discus. In introduction, the basic concepts of the lanthanides, OLED device materials, LEDs applications and ratiometric thermal sensors were discussed. The main aim and importance of the proposed work of the thesis was summarized in this chapter. In chapter 2, four europium complexes (Eu(TTA)3Phen-Ph-Ph, Eu(TTA)3Phen-mCF3-Ph Eu(TTA)3Phen-pCF3-Ph and Eu(TTA)3Phen-Fl-Ph) were designed and synthesized. The N1-functionalization of the phenanthro-imidazole ring by phenyl, substituted phenyl moiety (CF3, electron withdrawing group), fluorene and their influence on photophysical and electrochemical properties of EuIII complexes were determined by experimental and theoretical analyses. Among all the ligands, fluorene functionalized ligand shows white emission in the solid state. All the complexes (in solid and solution) showed the distinctive emission of EuIII ion at 612 nm, due to electric dipole transition (5D0→7F2). The absence of ligand emissions (solution, thin film and solid) in the PL emission spectra of EuIII complexes indicate that the efficient energy transfer from ligand to central metal ion (antenna effect), confirmed by DFT, TD-DFT. The HOMO-LUMO levels were determined by CV studies. Eu-complex was doped in PMMA matrix to fabricate the composite film devices (Eu(TTA)3Phen-pCF3-Ph shown highest quantum yield 78.7 %). The fluorene functionalized ligand integrated with InGaN LED chip (395 nm, forward bias 20 mA) show the potentiality of the ligand and shown white emission. The obtained efficient red emission from the fabricated LEDs (EuIII complexes coated on InGaN-based near UV LED) shown that the currently synthesized complexes could be a potential red component for warm white LEDs. In chapter 3, A new class of bipolar phenanthroimidazole based (N1 functionalization with Ph, mCF3, pCF3 and Fl) ligands and their efficient -diketonate EuIII complexes have been designed, synthesized, characterized successfully and their photophysical, electrochemical properties have also been investigated. All the ligands and complexes show similar UV-Visible absorption behaviour ( - *, at ~270, ~360 nm). Photoluminescence emission spectra of Eu-complexes and its ligands were carried out in solution form as well as in solid and thin film. The PL study indicates that the Eu-complex emits tunable emission due to incomplete/partial energy transfer (white (solution), red (solid)); whereas fluorene decorated Eu-complex shows narrow band red emission with appropriate CIE color gamut. The obtained PL emission clearly indicates that the efficient energy transfer encountered in case of fluorene based complex. The energy transfer mechanism for all the Eu-complexes was proposed based on combined experimental and theoretical study (DFT, TD-DFT). The PL lifetime of the EuIII complexes also supports the PL emission behaviour. The Judd–Ofelt spectral intensity parameters, electrochemical study and absolute QY (mCF3 based Eu-complex shows better QY of 75.9 %) of the Eu-complexes were also been investigated. White and red LED was fabricated using these complexes with near UV InGaN based LEDs (395 nm). In chapter 4, the efficient -diketonate red emitting carbazole-based EuIII complexes were synthesized and their photophysical, electrochemical properties were also been investigated. The PL study indicating that the efficient energy transfer from ligand to EuIII metal ion (dominant pathway) with appropriate CIE color gamut and time-dependent density functional theory (TD-DFT) also confirms the identical. The Judd-Ofelt theory to the emissive properties of EuIII complexes was investigated. The Eu(TTA)3Phen-Fl-CBZ complex shown better lifetime was found to be 0.64 ms. The absolute PL quantum yield (QY) of the complexes in solid is found to be 77.3 % and it possesses high thermal decomposition temperature (235C). The Judd-Ofelt intensity and related parameters were calculated for two complexes. The electrochemical analysis was shown narrow band gap energy (HOMO and LUMO). The PMMA film study of the complexes showed enhanced results than the solution. The fabricated Eu complexes with 395 nm emitted LED (InGaN) chips under 20 mA forward-bias current shown pure red emission and the corresponding CIE color coordinates are x = 0.66, y = 0.33. The obtained pure red emission is superior as compare to that of the solution and solid form of the complexes and the results are shown the presently investigated complexes find potential application in warm white LEDs. In chapter 5, A new diphenylamine (DPA) and carbazole (CBZ) functionalized ancillary ligands coordinated β-diketonate EuIII complexes shown incomplete or complete energy transfer from ligand to EuIII ion. Solvatochromism study of DPA based complex leads to balancing the primary RGB colors to obtain single molecule white emission. The temperature dependent PL study indicates that the DPA based complex could be used as ratiometric temperature sensor (color changes from blue to yellowish-red via white). In addition shown white emission with 0.34, 0.33 CIE coordinates. In the case of CBZ functionalized bipolar ligand and its corresponding β-diketonate EuIII complex shown efficient energy transfers from the ligand to EuIII center metal ion and emits narrow band red emission with apt CIE color gamut. TD-DFT calculations were performed to know the energies of the singlet (1S) and triplet (3T) levels for the bipolar ligand and shown good overlap between the ligand triplet level and EuIII excited level. The PLQY is found to be 44.4 %, whereas the DPA based complex shown comparatively less QY (supports the inefficient energy transfer). HOMO and LUMO energy levels energies (redox reaction) were calculated from the electrochemical analysis for the Eu-complexes. The synthesized EuIII complex was doped in PMMA with different percentage ratio and found to be concentration variation influence on emission intensity and symmetry. The CBZ-Eu-complex conjugated with near UV LED (395 nm) shown red emission with CIE color coordinates of 0.66, 0.33 and could find potential application in white LEDs. In chapter 6, the effect of functionalization of carbazole with spacer in C1 position and fluorine in N1 position in the phenanthroline-imidazole based bipolar ligand has been designed, synthesised, same is utilized to synthesise Eu(TTA)3Phen-Fl-O-CBZ complex and studied their photophysical properties. In addition, phenyl and fluorene functionalization in N1 position of phenanthro-imidazole ring (with alkoxy spacer) and its influence on photophysical properties of their binuclear Eu- complexes were systematically investigated. The mono and binuclear Eu-complexes emission spectra (pure red emission) clearly indicate that the complete energy transfer from ligand (L) to EuIII ion occurs, since there is no emission from ligand was encountered (confirmed by DFT and TD-DFT calculations). It is found that the spacer molecule can decrease the energy gap of HOMO-LUMO energy levels (2.6 eV) with respect to that of without spacer one and increment in the singlet and triplet energy levels was also observed, consequences efficient energy transfer (L to M). The enhanced QY observed by 1% doping with PMMA as compare with other doping concentrations (14.2%). Binuclear Eu show dominant electric dipole transition of EuIII ion (5D0→7F2, confirms the EuIII ion in the non-centrosymmetric site). The highest QY (59.5 %, for thin film) obtained for the Eu2(TTA)6(L2). The binuclear EuIII complexes were combined with InGaN near UV LED, obtained pure red emission with CIE color coordinate values x = 0.65, y = 0.34 and x = 0.66, y = 0.33 for Eu2(TTA)6(L1) and Eu2(TTA)6(L2), respectively. The obtained results indicate that the synthesized complexes are potential aspirant for light converting devices. In chapter 7, a series of organic chromophores or ancillary ligands (based on phenanthroimidazole) conjugated with triphenylamine or carbazole moieties were designed with and without spacer and studied their excited state photophysical properties by density functional theory and time-dependent density functional theory. The UV absorption analysis shown maxima around λmax 288, which is belongs to the -* transition of the ligands. The excited state photophysical properties reveal that the location of the triplet level found among three (1a-f, 2a-f, 3a-f) series 3a-f shown better energy matching with the excited state (5D0) of EuIII ion and could facilitate the energy transfer from ligand to Eu ion very efficient. In addition, the substituted phenyl moiety (mCF3 and pCF3) at N1-position in the phenanthro-imidazole ligand give additional benefits by reducing the triplet energy comparatively with other substitution that leads to efficient energy transfer from L to Eu ion in the complex could be expected. In addition, HOMO and LUMO calculations given lead that some of the designed ligands can also serve as host materials for triplet dopant in OLEDs. The systematic theoretical study is certainly leads to synthesis of best ligand molecules for Eu complexes. In chapter 8, the present works deals with molecular designing and synthesis of novel class bipolar or ancillary ligand for europium complexes and explore the possibility of using the same in white LEDs, temperature sensor and OLED applications. The observations and the conclusions derived from the present investigations are summarized in this chapter

    METHODOLOGIES FOR THE SYNTHESIS OF THIAHELICENE-BASED PHOSPHORUS DERIVATIVES AND THEIR APPLICATIONS IN ASYMMETRIC CATALYSIS

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    Helicenes are ortho-annulated polycyclic aromatic or heteroaromatic compounds endowed with inherent chirality due to the helical shape of their \u3c0-conjugated system, whose unique structural features and physicochemical properties have stimulated countless studies in several fields, including nanosciences, chemosensing, materials science, biomolecular recognition, and asymmetric catalysis. However, whilst axial, central and planar chirality have been largely exploited to build chiral phosphorus ligands and organocatalysts, helical chirality has been rather neglected so far in this field. This Ph.D. thesis aims to provide a meaningful contribution in the development of heterohelicene phosphorus derivatives, especially thiahelicene derivatives, as innovative chiral ligands to use in asymmetric organic and organometallic catalysis. In particular, we set up new classes of tetrathiahelicene(7-TH)-based phosphorus derivatives, including phoshine-borane complexes, phosphine oxides, free phosphanes, phosphathiahelicenes and the corresponding gold (I) complexes. Some of these systems have shown high efficiency as organocatalysts, as well as Au(I) complexes based on chiral phosphathiahelicene ligands were found to be efficient and selective catalysts in some challenging cycloisomerization reactions (ee up to 96%). The promising results obtained in this work will stimulate further developments and applications of these and analogous ligands to new asymmetric processes

    The Halogen Bond

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    The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design

    Investigation of Charge Transport in Conjugated Organic Materials

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    The demand for energy has increased dramatically with increase in population and industrialization. However, relying on traditional fossil fuels to meet those demands lead to climate change becoming an existential threat to the livelihood of humanity. Thus, to navigate the challenges of meeting the energy demand, researchers need to investigate pathways to pivot to more benign energy sources as well as discovering sustainable materials for a versatile range of energy applications. Conjugated organic materials have been of great interest for optoelectronic applications for the past 50 years to complement and/or substitute their inorganic counterparts. This work aims to design and investigate the charge transport properties of conjugated organic materials. This is achieved by providing a diverse toolbox of structure- property studies to further understand the behavior of doped organic materials and guide future development. In addition, this thesis shows an example of how such polymers can used in solar cells to replace an inorganic oxide. Further, a family of dopants along with investigation into their kinetic behavior is presented to be used in the future developments of polymer: dopant systems.Ph.D
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