The thesis presents detailed results of theoretical analyses based on extensive computer simulation studies with an aim to explore, quantify whenever possible, and understand structure and dynamics of polymers and proteins in several complex solvents. In order to make the Thesis coherent, we also study certain aspects of binary mixtures. Based on the phenomena studied, the thesis has been divided into four major parts: I. Dynamics of biological water: Distance dependent variation of dielectric constants in aqueous protein solutions II. Temperature dependent study of structural transformations in aqueous binary mixtures III. Conformation and dynamics of polymers in solution: Role of aqueous binary mixtures IV. Conformational change and unfolding dynamics of proteins: Role of sol-vent environment The above mentioned four parts have further been divided into thirteen chapters. In the following we provide a brief chapter-wise outline of the thesis. Part I consists of two chapters, where we focus on the study of dynamics of biological water and distance dependent variation of static and dynamic proper-ties (including dielectric constant) of water near different proteins. To start with, chapter 1 provides an introduction to the structure and dynamics of biological water. Here we discuss different experimental studies; including dielectric relaxation, NMR and salvation dynamics those explore the bimolecular hydration dynamics in great detail. We also discuss the wide range of computer simulation and theoretical studies that have been carried out to understand the dynamical behaviour of biological water. In chapter 2, we present our molecular dynamics simulation study to ex-plore the distance dependent static and dynamic behaviour of biological water near four different protein surfaces. Proteins are known to have large permanent dipole moments that can influence structure and dynamics of even distant water molecules. Therefore, distance dependence of polarization punctuation can provide important insight into the nature of biological water. We explore these aspects by studying aqueous solutions of four different proteins of different char-acteristics and varying sizes. We find that the calculated dielectric constants of the systems show a noticeable increment in all the cases compared to that of neat water. Total dipole moment auto time correlation function of water is found to be sensitive to the nature of the protein. We also define and calculate the effective dielectric constant of successive layers and find that the layer adjacent to protein always has significantly lower value (∼ 50). However, progressive layers exhibit successive increment of dielectric constant, finally reaching a value close to that of bulk 4–5 layers away. Theoretical analysis providing simple method for calculation of shellwise local dielectric constant and implication of these findings are elaborately discussed in this chapter. Part II deals with the temperature dependent study of aqueous DMSO and ethanol solutions and consists of three chapters. Chapter 3 provides a general introduction to the non-ideality (deviation from Raoult’s law) encountered in different binary mixtures. We discuss different theoretical models for treatment of binary mixtures. Finally we provide a systematic study about the non-ideality observed in aqueous binary mixtures. Here we discuss the anomalies observed in such systems and carry out a brief survey on the existing ideas of structural transformations associated with the solvation of a foreign molecule in water. In chapter 4, we discuss the results of temperature dependent study of struc-tural and dynamic properties of aqueous dimethyl sulfoxide (DMSO) mixture. It is now well-known that aqueous DMSO mixture exhibits signature of perco-lation driven structural aggregation at a mole fraction range xDMSO ≈ 0.15. We study the structural and dynamical change in this binary mixture below and above the percolation threshold along with decreasing temperature. Significant change in the molecular structure of DMSO as well as that of water is observed above the percolation threshold at a lower temperature, particularly at 200K. The structural arrangement of the DMSO molecules is found to be progressively more ordered with increasing DMSO concentration and decreasing temperature. On the other hand, water structure is found to be significantly deviated from tetrahedral arrangement in presence of DMSO clusters even at low temperature. The dynamics of water is also found to be considerably affected with increase of concentration and lowering of temperature. Similar phenomenon is observed for another amphiphilic molecule, ethanol, and has been discussed in chapter 5. Aqueous ethanol mixture is a widely studied solvent, both experimentally and using computer simulations. All the studies indicate several distinct salvation regimes. In recent molecular dynamics simulation studies, the reason for formation of micro-aggregates of ethanol is again attributed to percolation driven structural transformation. We carry out a temperature dependent study of water-ethanol binary mixture, particularly at low ethanol concentration to understand the molecular origin of such structural transformation. We find that the structural arrangement of ethanol as well as water molecules is similarly affected as that of DMSO with lowering of temperature. However, dynamics of water molecules in aqueous ethanol solution is found to be marginally affected, unlike the case of aqueous DMSO solution. We discuss the microscopic reason for such behaviour in a detailed manner. In Part III, we discuss the dynamics of linear polymer chains in different aqueous binary mixtures. Here we have three chapters. In chapter 6, we carry out a brief survey of the existing theories of polymers in solution. We discuss the quality of solvents depending on the preferred interactions between the polymer and the solvent or the polymer with its own. We also discuss the celebrated Flory-Huggins theory. We derive the expression of free energy of the Flory-Huggins theory in terms of the volume fraction of monomer and solvent molecules. In chapter 7, we discuss the results of our study of polymer dynamics in aqueous DMSO solution. We find that at a mole fraction 0.05 of DMSO (xDMSO ≈ 0.05) in aqueous solution, a linear polymer chain of intermediate length (n=30) adopts collapsed conformation as the most stable conformational state. The same chain exhibits an intermittent oscillation between the collapsed and the extended coiled conformations in neat water. Even when the mole fraction of DMSO in the bulk is 0.05, the concentration of the same in the first hydration layer around the polymer is found to be as large as 17 %. Formation of such hydrophobic environment around the hydrocarbon chain may be viewed as the reason for the collapsed conformation gaining additional stability. We find a second anomalous behaviour to emerge near xDMSO ≈ 0.15 that is attributed to the percolation driven structural aggregation of DMSO that lowers the relative concentration of the DMSO molecules in the hydration layer. In chapter 8, we carry out similar study of linear polymer chain in water– ethanol binary mixture. In this case also, we find a sudden collapse of the poly-merat xEtOH ≈ 0.05. Since ethanol molecules are known to form micro-aggregates in this concentration range, stability of collapsed state of polymer at this con-centration is anticipated to be correlated to this phenomenon. In fact, a purely hydrophobic polymer chain, in its collapsed form is anticipated to assist in the formation of spanning cluster comprised of hydrophobic ethyl groups at this concentration range thereby facilitating the percolation transition. We discuss these prospects in this chapter. Part IV deals with the solvent sensitivity to the conformational change and unfolding dynamics of protein. Part IV consists of five chapters. In chapter 9, we develop an understanding of protein folding and unfolding dynamics by discussing the fundamental theories developed in the last few decades. We also discuss the major role of solvents in stabilizing or destabilizing the native, ordered state. In chapter 10, we present a detailed study of unfolding of a small protein, chicken villin headpiece (HP36) in water-ethanol binary mixture, using molecular dynamics simulations. The prime objective of this work is to explore the sensitivity of protein dynamics towards increasing concentration of the cosolvent and unravel essential features of intermediates formed in the unfolding path-way. In water–ethanol binary mixtures, HP36 is found to unfold partially, under ambient conditions, that otherwise requires temperature as high as ∼ 600K to denature in pure aqueous solvent. The study unravels certain interesting aspects about the pathway of unfolding, guided by the formation of unique intermediates. Unfolding is initiated by the separation of hydrophoic core comprising three phenylalanine residues (Phe7, Phe11, Phe18). This separation initiates the melting of the helix2 of the protein. However, with an increase of cosolvent concentration different partially unfolded intermediates are found to be formed. We attribute the emergence of such partially unfolded states to the preferential solvation of hydrophobic residues by the ethyl groups of ethanol. We explore and subsequently quantify the detailed dynamics of unfolding in water-ethanol that appear to be more complex and sensitive to solvent composition. With an aim to develop a general understanding of the role of water–ethanol binary mixture in facilitating anomalous conformational dynamics of proteins, we carry out combined theoretical and experimental studies to explore detailed structural change of a larger protein, Myoglobin with increasing ethanol concentration. These studies are described in chapter 11. In agreement with our pre-vious observations, we identify in this case two well-defined structural regimes, one at xEtOH ≈ 0.05 and the other at xEtOH ≈ 0.25, characterized by formation of distinct partially folded conformations and separated by a unique partially unfolded intermediate state at xEtOH ≈ 0.15. We also find non-monotonic com-position dependence of (i) radius of gyration (ii) long range contact order (iii) residue specific solvent accessible surface area of tryptophan (iv) circular dichro-ism spectra and UV-absorption peaks. Multiple structural transformations, well-known in water-ethanol binary mixture, appear to have considerably stronger effects on the conformation and dynamics of protein Myoglobin. In chapter 12, we explore the free energy surface of unfolding pathway through umbrella sampling, for the small globular alpha-helical protein chicken-villin headpiece (HP36) in three different solvent conditions (water, xDMSO ≈ 0.15 and xDMSO ≈ 0.3). Recently established as a facilitator of helix melting, DMSO is found to be a good denaturant for HP36 and at a mole fraction of xDMSO ≈ 0.3, complete melting of the protein is ensured. The unfolding proceeds through initial separation or melting of the same aggregated hydrophobic core that com-prises three phenylalanine residues (Phe7, Phe11 and Phe18) accompanied by simultaneous melting of the helix2. Unfolding is found to be a multistage process involving crossing of three consecutive minima and two barriers at the initial stage. At a molecular level, Phe18 is observed to reorient itself towards other hy-drophobic grooves to stabilize the intermediate states. We identify the configuration of intermediates in all the solvent conditions which are found to be unique for the corresponding minima with similar structural arrangement. Consider-able softening of the barriers is observed with increasing DMSO concentration. Higher concentration of DMSO tunes the unfolding pathway by destabilizing the third minimum and stabilizing the second one, indicating the development of solvent modified, less rugged pathway. Chapter 13 provides a detailed microscopic mechanism of DMSO induced unfolding of HP36. We analyze the free energy contours of the protein HP36, obtained from molecular dynamics simulation in xDMSO ≈ 0.15 and xDMSO ≈ 0.3. The most probable intermediates obtained from the free energy contours are found to be similar to those obtained from umbrella sampling which again sup-ports the fact that the melting proceeds through formation of a series of unique intermediates. We characterize the preferential hydrophobic salvation of the hydrophobic core that drives the melting of secondary structure, by calculating time dependent radial distribution function and identifying the formation of strong orientation order between methyl groups of DMSO and phenyl alanine residues. Finally we employ Kramer’s rate equation to calculate the rate of bar-rier crossing that reveals significantly faster rate of unfolding with increasing DMSO concentration that is in agreement with simulation results. Whenever possible, we have discussed the scope of future work at the end of each chapter.

High dielectric constant materials have tremendous impact on miniaturization of devices that are used in various applications like wireless communication systems, microelectronics, global positioning systems, etc. To store electric charge in a very small space necessarily needs a capacitor with very high dielectric constant. Thus, these materials are very important in fabricating capacitors, or metal oxide semiconductor filed effect transistor (MOSFET). Among the existing commercially available devices, silicon-based microelectronic devices are commonly used based on the moderately stable dielectric constants of silicon with low losses and minimal temperature and frequency dependence. However, now-a-days, the perovskite based transition metal oxides have drawn attention that have the ability to fulfill all the requirements for being a good dielectric material in all the industrial applications. In this thesis we have studied a few selected perovskite based transition metal oxide systems in terms of their dielectric and magnetic behaviour. In Chapter 1, we have have given brief introductions about the some application of dielectric materials and the origin of dielectric and magnetic properties in the materials. We have also discussed about the polarisation in the dielectric materials to understand it’s frequency dependence and also to formalise different relaxation behaviour with the help of physical and mathematical explanation. In Chapter 2, we describe the various methodologies adopted in this thesis. In Chapter 3, we have studied the dielectric behaviour of Nd2NiMnO6, a rare earth based double perovskite ferromagnetic insulator. We successfully synthesised and characterised the compounds, settled the valency issues with the help of temperature dependent XAS of the transition metal atom in contrast to the existing controversy available in literature. We have found that this material shows relaxor kind behaviour with a colossal dielectric constant value. We have studied in details the origin of the colossal dielectric constant and the relaxation behaviour along with the a.c and d.c. transport properties. We have shown the origin of the ferromagnetism (TC ∼ 200 K) with a low temperature antiferromagnetic ordering (TN ∼ 55 K) with the help of detailed studies of temperature dependent d.c., a.c. magnetism and their XMCD. We have also investigated the isothermal variation of magnetodielectric and magnetoresistance behaviour as a function of magnetic field and their origin. In Chapter 4,we study the effect of cation anti-site disorder on the magnetic, dielectric and transport properties of another rare earth based ferromagnetic double perovskite insulator La2NiMnO6 by controlling different extent of anti-site disordered. We have confirmed the valency of the transition metal cations using XAS technique and followed by shown, different types of magnetic interaction between the transition metal cations using d.c magnetic, quantitative XMCD analysis and the origin of large dielectric response, a.c. transport & dielectric relaxation using temperature variation dielectric measurement as an experimental evidence in contrast of our previous speculation published in literature. We further have studied, the coupling between the magnetic and electric spin through isothermal magnetodielectric measurement. In Chapter 5, we have successfully synthesised and characterised a solid solution of YMnxIn1−xO3 series via different mol % of In doping in the multiferroic YMnO3 system. YMnO3 is a well known multiferroic material studied rigorously during past few decades. We have seen, YMnO3 which has a antiferromagnetic ordering temperature of ∼ 75 K suppressed with increasing the dopant concentration In. We have figured out the effect of In doping in the suppression of multiferroic phase and extended it to the dielectric properties. We have found that, the temperature dependence of dielectric constant shows an anomaly at the magnetic ordering temperature and studied magnetodielectric coupling. We have also investigated the temperature variation of dielectric relaxation and a.c. transport behaviour as a function of composition. In Chapter 6, we have identified the phase seperation and proposed a phase diagram as function of Gd doping in the Ho2−xGdxCuTiO6 double perovskite, where two end member, namely Ho2CuTiO6 and Gd2CuTiO6 are found to be in two different crystallographic phase as, hexagonal (P63cm) and orthorhombic (Pnmm), respectively. We have characterised the valency of the transition metal cations using XAS.We have seen very less temperature and frequency dependence of dielectric constant in hexagonal phase in compare to the orthorhombic phase and tried to figuring out from experimental analysis by performing temperature dependence dielectric const measurement. We also have shown the effect of doping in the origin of dielectric relaxation, a.c transport and magnetic behaviour of this system. In Chapter 7, we have synthesised and characterised successfully two different rare earth based layered perovskite La3Cu2VO9 and La4Cu3MoO12 compounds are of centrosymmetric space group. We have figured it of the valency of the different atoms present in the compound using XAS. We also do have observed the good temperature stability of dielectric constant of these materials and explored origin of mechanism in the dielectric relaxation, a.c. transport property by performing the temperature dependance dielectric measurement. The magnetic structure also have shown with the help of d.d. magnetic measurements. In Appendix A, we have seen the very stable dielectric constant constant from very low to above room temperature of the 2D nano PbS. The frequency stability of dielectric constant is also remarkable in compare to bulk PbS values available in literature. We have explored the origin of the conductivity and relaxation mechanism performing dielectric constant measurement. In conclusion, we investigate, in this thesis, dielectric properties of different transition metal oxides system and the mechanism of dielectric relaxation, a.c, d.c transport and their origin of magnetic response.

Extensive research work was carried out in past few decades to synthesize new compounds with extended structures by employing various organic linkers and metals. A large number of potential applications of these coordination polymer materials were explored as it contains both inorganic metals as well as organic molecules. The large open pores of coordination polymer compounds were explored for applications such as absorption, separation, and catalysis etc. whereas the framework part provides a model system to study physical properties such as magnetism, luminescence, ferroelectricity etc. We were mainly interested in designing new magnetic materials with extended structures which is the primary objective of this thesis. To study this a systematic investigations are carried out with azide bridged copper(II) compounds. Azide is a versatile ligand which possesses a large number of bridging modes. On the other hand, the coordination flexibility offered by the copper centres makes it to possess diverse coordination number (4-6) as well as geometry. Copper-azide compounds were synthesized at room temperature and the structure was determined using single-crystal X-ray diffraction studies. Structure and magnetic behavior of the copper-azide compounds were studied and discussed here in this thesis. Further, we have studied selective absorption and separation of aliphatic nitrile compounds by employing a two-dimensional interdigitated coordination polymer. In addition, transformation studies of a Ni5 cluster to a Ni9 cluster have also been carried out. Chapter 1 of this thesis presents a brief overview of azide based compounds and summarizes important copper-azide compounds and their magnetic behavior. In chapter 2, synthesis, structure, and magnetic behavior of two-dimensional copper-azide based compounds have been presented. Field dependent magnetic studies were also carried out for all the compounds. Chapter 3 presents the synthesis, structure, and magnetic behavior of copper-azide compounds where 1,2-diaminopropane was employed as a site blocking agent. In chapter 4, the synthesis, structure, and magnetic behavior of two isostructural three-dimensional copper-azides are presented. In chapter 5, synthesis, structure, and magnetic behavior of the azide based one and two-dimensional compounds are presented. Chapter 6 presents synthesis and structure of a two-dimensional inter-digitated coordination polymer compounds. The selective absorption and separation of aliphatic nitriles were also presented in this chapter. In chapter 7, synthesis, structure, and magnetic behavior of Ni clusters are presented. A transformation study to convert a Ni5 cluster to Ni9 cluster was also carried out and presented in this chapter.

The metal-organic framework (MOF) compounds have witnessed rapid growth in the past decade and currently emerged as a highly unique area in the field of chemistry, materials science, and multiple branches of engineering. It presents applications in diverse fields such as gas sorption, catalysis, ionic conductivity, sensing etc. These compounds are built by the inorganic metal ions which are bridged by organic linkers to form extended structures. These compounds are mainly synthesized by either one-pot synthesis or in a sequential manner. In the former case, the inorganic metal ions and the respective organic linker are reacted together in a particular solvent or solvent mixture, whereas in the later case, a metalloligand is prepared by using the organic linker and the primary metal ion, which react with the secondary metal ion forming the desired structure. In this thesis, the synthesis of metal-organic framework compounds by one-pot synthesis as well as the sequential synthesis is presented. The structures of all the synthesized compounds have been determined by single crystal X-ray diffraction technique. The prepared compounds were employed in the study of sensing of nitroaromatic compounds, toxic metal ions and highly oxidizing anions. In addition, detailed studies of heterogeneous catalysis employing the prepared MOFs were investigated along with catalysis by metal nanoparticle incorporated within MOFs. In select cases, the labile nature of the lattice water molecules was established by performing in-situ single crystal to single crystal (SCSC) structural transformation studies. In addition, the proton conductivity and the magnetic behavior have also been studied. Chapter 1 of the thesis presents a brief overview on metal-organic framework compounds and summarizes its various important properties. In chapter 2, the synthesis, structure, and characterization of heterometallic metal-organic framework compounds using 2-mercaptonicotinic (H2mna) and Cu(I) / Ag(I) based two metalloligands, [Cu6(Hmna)6] and [Ag6(Hmna)2(mna)4](NH4)4 are presented. In chapter 3, we present the synthesis, structure and nitroaromatic sensing behavior of [Ag6(mna)6](NH4)6 metalloligand based heterometallic metal-organic framework compounds. In chapter 4, the synthesis, structure and Lewis acid catalytic behavior of 6-mercaptonicotinic acid based heterometallic metal-organic framework compounds are presented. In chapter 5, the stabilization of the palladium nanoparticles in the newly synthesized 1,10-phenanthroline based metal-organic framework compounds and their catalytic behavior is presented. In chapter 6, we present the synthesis, structure and the sensing behavior of hazardous chemicals such as toxic metal ions and highly oxidizing anions. In addition, the adsorption and desorption of synthetic dye molecules by the metal-organic framework compounds are also presented.

Electronic and optical properties of semiconducting nanocrystals, that can be engineered and manipulated by various ways like varying size, shape, composition, structure, has been a subject of intense research for more than last two decades. The size dependency of these properties in semiconductor nanocrystals is direct manifestation of the quantum confinement effect. Study of electronic and optical properties in smaller dimensions provides a platform to understand the evolution of fundamental bulk properties in the semiconductors, often leading to realization and exploration of entirely new and novel properties. Not only of fundamental interests, the semiconductor nanocrystals are also shown to have great technological implications in diverse areas. Besides size tunable properties, introduction of impurities, like transition metal ions, gives rise to new functionalities in the semicon-ductor nanocrystals. These materials, termed as doped semiconductor nanocrystals, have been the subject of great interest, mainly due to the their interesting optical properties. Among different transition metal doped semiconductor nanocrystals, manganese doped systems have drawn a lot on attention due to their certain advantages over other dopants. One of the major advantages of Mn doped semiconductor nanocrystals is that they do not suffer from the problem of self-absorption of emission, which quite often, is consid-ered detrimental in their undoped counterparts. The doped nanocrystals are known to produce a characteristic yellow-orange emission upon photoexcitation of the host that is relatively insensitive to the surface degradation of the host. This emission, originating from an atomic d-d transition of Mn2+ ions, has been a subject of extensive research in the recent past. In spite of the spin forbidden nature of the specific d-d transition, namely 6A1 −4 T1, these doped nanocrystals yield intense phosphorescence. However, one major drawback of utilizing this system for a wide range application has been the substantial inability of the community to tune the emission color of Mn-doped systems in spite of an intense effort over the years; the relative constancy of the emission color in these systems has been attributed to the essentially atomic nature of the optical transition involving localized Mn d levels. Interestingly, however, the Mn emission has a very broad spectral line-width in spite of its atomic-like origin. While the long (∼ 1 ms) emission life-time of the de-excitation process is well-studied and understood in terms of the spin and orbitally forbidden nature of the transition, there is little known concerning the process of energy transfer to the Mn from the host in the excitation step. In this thesis, we have studied the ultrafast dynamic processes involved in Mn emission and addressed the issues related to its tunability and spectral purity. Chapter 1 provides a brief introduction to the fundamental concepts relevant to the studies carried out in the subsequent chapters of this thesis. This chapter is started with a small preview of the nanomaterials in general, followed by a discussion on semiconducting nanomaterials, evolution of their electronic structure with dimensions and size as well as the effect of quantum confinement on their optical properties. As all the semiconducting nanomaterials studied in the thesis are synthesized via colloidal synthesis routes, a separate section is devoted on colloidal semiconducting nanomaterials, describing various ways of modifying or tuning their optical properties. This is followed by an introduction to the important class of materials “doped semiconductor nanocrystals”. With a general overview and brief history of these materials, we proceed to discuss about various aspects of manganese doped semiconductor nanocrystals in great details, highlighting the origin of the manganese emission and the associated carrier dynamics as well as different reported synthetic strategies to prepare these materials. The chapter is closed with the open questions related to manganese doped semiconductor nanocrystals and the scope of the present work. Chapter 2 describes different experimental and theoretical methods that have been employed to carry out different studies presented in the thesis. It includes common experimental techniques like UV-Vis absorption spectroscopy, steady-state and time-resolved photoluminescence spectroscopy used for optical measurements, X-ray diffraction, trans-mission electron microscopy and atomic absorption spectroscopy used for structural and elemental analysis. Experimental tools to perform special studies like transient absorption and single nanocrystal spectroscopy are also discussed. Finally, theoretical fitting method used to analyse various spectral data has been discussed briefly. Chapter 3 deals with the dynamic processes involved in the photoexcitation and emission in manganese doped semiconductor nanocrystals. For this study, Mn doped ZnCdS alloyed nanocrystal has been chosen as a model system. There are various radiative and nonrdiative recombination pathways of the photogenerated carriers and they often compete with each other. We have studied the dynamics of all possible pathways of carrier relaxation, viz. excitonic recombination, surface state emission and Mn d-d transition. The main highlight of this chapter is the determination of the time-scale to populate surface states and the Mn d-states after the photoexcitation of the host. Employing femtosecond pump-probe based transient absorption study we have shown that the Mn dopant states are populated within sub-picosecond of the host excitation, while it takes a few picoseconds to populate the surface states. Keeping in mind the typical life-time of the excitonic emission (∼ a few ns), the ultra-fast process of energy transfer from the host to the Mn ions explains why the presence of Mn dopant ions quenches the excitonic as well as the surface state emissions so efficiently. Chapter 4 presents a study of manganese emission in ZnS nanocrystals of different sizes. By varying the size of the ZnS host nanocrystal, we show that one can tune the Mn emission over a limited range. In particular, with a decrease in host size, the Mn emission has been observed to red-shift. We have attributed this shift in Mn emission to the change in the ratio of surface to bulk dopant ions with the variation of the host size, noting that the strength of the ligand field at the Mn site should depend on the position of the Mn ion relative to the surface due to a systematic lattice relaxation in such nanocrystals. The ligand field affects the emission wavelength directly by controlling the splitting of the t2 and e levels of Mn2+ ions. The surface dopant ions experience a strong ligand field due to distorted tetrahedral environment which leads to larger splitting of these t2 and e states. We further corroborated these results by performing doping concentration dependent emission and life-time studies. In Chapter 5 addresses two fundamental challenges related to manganese photolumines-cence, namely the lack of a substantial emission tunability and presence of a very broad spectral width (∼ 180-270 meV). The large spectral width is incompatible with atomic-like manganese 4T1 −6 A1 transition. On the other hand, if this emission is atomic in nature, it should be relatively unaffected by the nature of the host, though it can be manipulated to some extent as discussed in Chapter 3. The lack of Mn emission tunability and spectral purity together seriously limit the usefulness of Mn doped semiconductor nanocrystals. To understand why the Mn emission tunability range is very limited (typically 565-630 nm) and to understand the true nature of this emission, we carried out single nanocrystal imaging and spectroscopy on Mn doped ZnCdS alloyed nanocrystals. This study reveals that Mn emission, in fact, can vary over a much wider range (∼ 370 meV) and exhibits widths substantially lower (∼ 60-75 meV) than reported so far. We explained the occur-rence of Mn emission in this broad spectral range in terms of the possibility of a large number of symmetry inequivalent sites resulting from random substitution of Cd and Zn ions that leads to differing extent of ligand field contributions towards the splitting of Mn d-levels. The broad Mn emission observed in ensemble-averaged measurements is the result of contribution from Mn ions at different sites of varying ligand field strengths inside the NC. Chapter 6 presents a synthetic strategy to strain-engineer a nanocrystal host lattice for a controlled tuning of the ligand field effect of the doped Mn sites. It is realized synthesizing a strained quantum dot system with the structure ZnSe/CdSe/ZnSe. A larger lattice parameter of CdSe compared to that of ZnSe causes a strain field that is maximum near the interface, gradually decreasing towards the surface. We control the positioning of Mn dopant ions at different distances from the interface, thereby doping Mn at different predetermined strain fields. With the help of this strain engineering, we are able to tune Mn emission across the entire range of the visible spectrum. This strain induced tuning of Mn emission is accompanied by life-times that is dependent on the emission energy which has been explained in terms of perturbation effect on the Mn center due to the strain generated inside the quantum dot. The spectacular emission tuning has been explained by modelling the quantum dot system as an elastic continuum containing three distinct layers under hydrostatic pressure. From this modelling, we found that the strain is max-imum at the interface and decreases continuously as one goes away from the interface. We also show that the Mn emission maximum red shifts with increasing distance of the dopants from the maximum strained region. In summary, we have performed a study on the photophysical processes in manganese doped semiconductor nanocrystals. We have emphasized in understanding of different dynamic processes associated with the manganese emission and tried to understand the true nature of manganese emission in a nanocrystal. This study has brought out some new aspects of manganese emission and opened up possibilities to tune and control manganese emission by proper design of the host material.

The research work reported in this thesis is focused on the chiral analysis, quantification of enantiomeric composition, assignment of absolute configuration of molecules with chosen functional groups. The weak intra-molecular hydrogen bonding interactions are detected by exploiting several multinuclear and multi-dimensional techniques. Pulse sequences have been designed to manipulate the spin dynamics to derive specific information from the complex NMR spectra encountered in diverse situations. Broadly, the thesis can be classified in to three sections. The section I containing two chapters reports the introduction of new chiral auxiliaries and protocols developed for enantiomeric discrimination, measurement of enantiomeric contents, assignment of absolute configuration for molecules possessing specific functional groups using chiral solvating and derivatizing agents. The section II, reports NMR experimental evidence for the observation of the rare type of intramolecular hydrogen bonds involving organic fluorine in biologically important organic molecules, that are corroborated by extensive DFT based theoretical calculations. The section II also discusses the H/D exchange mechanism as a tool for quantification of HB strengths in organic building blocks. The section III reports the two different novel NMR methodologies designed for deriving information on the scalar interaction strengths in an orchestrated manner. The designed sequences are able to completely eradicate the axial peaks, prevents the evolution of unwanted couplings and also yields ultrahigh resolution in the direct dimension, permitting the accurate measurement of scalar couplings for a particular spin. The brief summary about each chapter is given below. Chapter 1 provides a general introduction to one and two dimensional NMR spectroscopy. The pedagogical approach has been followed to discuss the conceptual understanding of spin physics and the NMR spectral parameters. The basic introduction to chirality, existing approaches in the literature for discrimination of enantiomers and the assignment of absolute configuration of molecules with chosen functional groups and their limitations are briefly discussed. The brief introduction to hydrogen bond, experimental methods to obtain the qualitative information about the strengths of hydrogen bonds, and the theoretical approaches employed in the thesis to corroborate the NMR experimental findings have been provided. The mechanism of H/D exchange, the utilization of exchange rates to derive strengths of intra-molecular hydrogen bond in small molecules have also been discussed. This chapter builds the bridge for the rest of the chapters. Each of these topics are discussed at length in the corresponding chapters. Part I: NMR Chiral Analysis: Novel Protocols Chapter 2 discusses a simple mix and shake method for testing the enantiopurity of primary, secondary and tertiary chiral amines and their derivatives, amino alcohols. The protocol involves the in-situ formation of chiral ammonium borate salt from a mixture of C2 symmetric chiral BINOL, trialkoxyborane and chiral amines. The proposed concept has been convincingly demonstrated for the visualization of enantiomers of a large number of chiral and pro-chiral amines and amino alcohols. The protocol also permits the precise measurement of enantiomeric composition. The significant advantage of the protocol is that it can be performed directly in the NMR tube, without any physical purification. The structure of the borate complex responsible for the enantiodifferentiation of amines has also been established by employing multinuclear NMR techniques and DFT calculations. From DOSY and 11B NMR experiments it has been ascertained that there are only two possible complexes or entities which are responsible for differentiating enantiomers. From the combined utility of DFT calculations and the 11B NMR chemical shifts, the structure of the borate complex has been determined to be an amine-coordinated complex with the N atom of the amine. Chapter 3 discusses a simple chiral derivatizing protocol involving the coupling of 2-formylphenylboronic acid and an optically pure [1,1-binaphthalene]-2,2-diamine for the rapid and accurate determination of the enantiopurity of hydroxy acids and their derivatives, possessing one or two optically active centres. It is established that this protocol is not only rapid method for discrimination of enantiomers but also highly effective for assigning the absolute configuration of various chiral hydroxy acids and their derivatives. The developed protocol involves the coupling of 2-formylphenylboronic acid with (R)-[1,1-binaphthalene]-2,2-diamine, and 2-formylphenylboronic acid with (S)-[1,1-binaphthalene]-2,2-diamine as chiral derivatizing agents. The absence of aliphatic peaks from the derivatizing agent, large chemical shift separation between the discriminated peaks of diastereomers, and the systematic change in the direction of displacement of peaks for an enantiomer in a particular diastereomeric complex, permitted the unambiguous assignment of absolute configuration. Part II : Rare Type of Intramolecular Hydrogen Bonding In chapter 4 The rare occurrence of intramolecular hydrogen bonds of the type N–H˖˖˖F–C, in the derivatives of imides and hydrazides in a low polarity solvent, is convincingly established by employing multi-dimensional and multinuclear solution state NMR experiments. The observation of 1hJFH, 2hJFN, and 2hJFF of significant strengths, where the spin polarization is transmitted through space among the interacting NMR active nuclei, provided strong and conclusive evidence for the existence of intra-molecular hydrogen bonds. Solvent induced perturbations and the variable temperature NMR experiments unambiguously supported the presence of intramolecular hydrogen bond. The two dimensional HOESY and 15N–1H HSQC experiments reveals the existence of multiple conformers in some of the investigated molecules. The 1H DOSY experimental results discarded any possibility of self or cross-dimerization of the molecules. The results of DFT based calculations, viz., Quantum Theory of Atoms In Molecules (QTAIM) and Non Covalent Interaction (NCI), are in close agreement with the NMR experimental findings. In chapter 5 the rates of hydrogen/deuterium (H/D) exchange determined by 1H NMR spectra have been utilized to derive the strength of hydrogen bonds and to monitor the electronic effects in the site-specific halogen substituted Benz amides and anilines. The theoretical fitting of the time dependent variation in the integral areas of 1H NMR resonances to the first order decay function permitted the determination of H/D exchange rate constants (k) and their precise half-lives (t1/2) with high degree of reproducibility. The comparative study also permitted the determination of relative strengths of hydrogen bonds and the contribution from electronic effects on the H/D exchange rates. Part III: Novel NMR Methodologies for the Precise Measurement of 1H-1H Couplings Chapter 6 describes two novel NMR methodologies developed for the precise measurement of 1H-1H couplings. Poor chemical shift dispersion and the pairwise interaction among the entire coupled network of protons results in the severely complex and overcrowded one dimensional 1H NMR spectra, hampering both the resonance assignments and the accurate determination of nJHH. The available two-dimensional selective refocusing (SERF) based experiments suffer from the evolution of magnetization from uncoupled protons as intense uninformative axial peaks. This creates ambiguity in the identification of peaks belonging to the coupled partners of a selectively excited proton, hindering the extraction of their interaction strengths. This challenge has been circumvented by designing two novel experimental technique, cited as “Clean-G-SERF” and “PS-Clean-G-SERF”. The Clean-G-SERF technique completely eradicates the axial peaks and suppresses the evolution of unwanted couplings while retaining only the couplings to the selectively excited proton. The method permits the accurate determination of spin-spin couplings even from a complex proton NMR spectrum in an orchestrated manner. The PS-Clean-G-SERF technique has been designed for the complete elimination of axial peaks and undesired couplings, with a blend of ultra-high resolution achieved by real time broad band mononuclear decoupling has been discussed in this chapter. The spin dynamics involved in both these pulse sequences have been discussed. The diverse applications of both these novel experiments have been demonstrated.

This thesis reports a passive method for Fermi level regulation in quantum dot assemblies through ground state transfer between QDs. Here, ZnTe/CdS, and PbSe/CdSe core/shell QDs were used as valence band electron donors, while Cu containing CdS or ZnSe acts as electron acceptor QDs. Prior to study of ground state charge transfer process, this report discusses the synthesis of ZnTe/CdS, and PbSe/CdSe core shell QDs, which are later used to study charge transfer. Since ZnTe QDs are unstable and prone to oxidation, a CdS coated ZnTe QDs were used. Growing a CdS shell on ZnTe core is difficult because high reduction potential of Te. To overcome this problem, partially reduced sulphur is used for the synthesis of ZnTe/CdS. The peculiar optical properties exhibited by ZnTe/CdS also have been discussed. Even though the synthesis of Lead chalcogenide nanoparticles has been investigated previously, certain inconsistencies between the behavior expected from known mechanisms and empirical observations. An anion exchange mechanism is proposed and demonstrated to be involved in PbSe formation. Both ZnTe and PbSe based QDs are extensively used to study hole injection and copper containing QDs were used as acceptors. The charge transfer has been studied using optical spectroscopy. The structure and composition of the assemblies was identified using powder crystallography, electron-microscopy and composition analysis. The unique physical and chemical properties of these materials are exciting both fundamentally as well as from the point of view of applications.

Electrochemical capacitors or supercapacitors or ultracapacitors are potential energy storage devices that could help bringing major advances in future energy storage applications. Unlike batteries that store energy in chemical reactants capable of generating charge, electrochemical capacitors store energy directly through charge separation. Most electrochemical capacitors rely on carbon-based structures utilizing electrical double-layer capacitance effect. By contrast, a pseudocapacitor relies on charge stored due to fast faradaic charge-transfer processes with surface atoms. A combination of faradaic and non-faradaic components would generate hybrid electrochemical capacitors or hybrid ultracapacitors that attain high capacitance for pulse power and sustained energy. This thesis comprises studies pertaining to design, development and applications R&D on substrate-integrated lead-carbon hybrid ultracapacitors. The thesis comprises ten chapters. Chapter 1 is a brief introduction on essentials of electrochemical capacitors explaining their operating principles, classification and applications. Chapter 2 describes studies on materials for electrical double-layer capacitors. Activated carbons are the most common materials for electrical double-layer capacitors. Various activated carbon samples are screened as suitable materials for electrical double-layer capacitor followed by their optimization under varying experimental conditions to form the negative plate in the substrate-integrated lead-carbon hybrid ultracapacitor. Chapter 3 deals with the studies on design and development of 2 V substrate-integrated lead-carbon hybrid ultracapacitors with flooded, absorbent-glass-mat and silica-gel sulfuric acid electrolyte configurations. Lead-carbon hybrid ultracapacitors comprise substrate-integrated lead dioxide sheets as positive plates and high surface-area-carbon-coated graphite-sheets as negative plates. Operating principle for 2 V lead-carbon hybrid ultracapacitors is explained and optimization of their operating conditions along with their electrochemical performance is studied. Chapter 4 is a study on the integration of 2 V substrate-integrated lead-carbon hybrid ultracapacitors to 12 V devices. 12 V substrate-integrated lead-carbon hybrid ultracapacitors with flooded, absorbent-glass-mat and silica gel sulfuric acid electrolyte are developed by connecting six 2 V cells in series. These hybrid ultracapacitors exhibit high power-density values and excellent cycle-life. The problem of uneven performance among the six 2 V cells in the 12 V hybrid ultracapacitors is addressed and resolved by applying voltage-management cell-balancing circuitry. Chapter 5 details the studies on kilo-Farad range 12 V substrate-integrated lead-carbon hybrid ultracapacitors. The hybrid ultracapacitors are performance tested through a standard protocol. Thermal runaway in these hybrid ultracapacitors at high load currents is studied by thermal imaging. Studies on performance comparison between 12 V lead-carbon hybrid ultracapacitors with substrate-integrated and conventional pasted-positive plates are presented in Chapter 6. For substrate-integrated-positive plate lead-carbon hybrid ultracapacitors, capacitance and energy-density values are lower but power-density values are higher than pasted-positive plate configuration due to their shorter response-time. Accordingly, internal resistance values are lower for substrate-integrated lead-carbon hybrid ultracapacitors. Both types of lead-carbon hybrid ultracapacitors exhibit similar faradaic efficiency and cycle-life in excess of 100,000 pulse charge/discharge cycles with only a nominal loss in their capacitance values. Chapter 7 is a study on the design and development of low-cost substrate-integrated lead-carbon hybrid ultracapacitors using poly-aniline organic metal. The hybrid ultracapacitor employs flexible exfoliated graphite sheets as negative plate current-collectors, which are coated with a thin layer of poly-aniline to provide good adhesivity to activated carbon layer and good substrate-conductivity. These ultracapacitors are estimated to cost about 4 US$/Wh as compared to 20-30 US$/Wh for presently available commercial ultracapacitors. In Chapter 8, an application R&D study on the suitability of a substrate-integrated lead-carbon hybrid ultracapacitor bank in powering medical gadgets is described. A practical application that provides 30 W power back-up to medical gadgets for use in grid-power-deficient rural areas is presented. Chapter 9 is another application R&D study in realizing a photovoltaic stand-alone lighting system using substrate-integrated lead-carbon hybrid ultracapacitors. At present, harnessing solar electricity generated through photovoltaic cells with lead-acid batteries remains the most compelling option. But lead-acid batteries have encountered problems in photovoltaic installations, mainly due to their premature failure. To circumvent this problem, substrate-integrated lead-carbon hybrid ultracapacitors are developed for solar energy storage for a lighting application. The last Chapter of the thesis comprises field studies on substrate-integrated lead-carbon hybrid ultracapacitors. In the study, hybrid ultracapacitors are installed for lighting applications for field tests. Grid-power chargers and mechanical dynamos are introduced as fast-charging tools for hybrid ultracapacitors. It is hoped that the studies presented in this thesis would constitute a worthwhile contribution to science and technology of electrochemical capacitors. Considering the technology need, availability, safety and cost, substrate-integrated lead-carbon hybrid ultracapacitors are set to play a seminal role in future energy storage and management.

The past few decades have witnessed an almost exponential increase in interest in the field of metal organic frameworks (MOFs), which can be evidenced from the large number of scientific articles being published routinely in this area. The MOFs are crystalline hybrid materials built via the judicial use of inorganic metal ions and organic linkers, thereby bridging the gap between purely inorganic and organic materials. The structural versatility and the potential tunability of the MOFs imparts unique physicochemical and thermomechanical properties, which have rendered them immensely useful in the branches of chemistry, material science, physics, biology, nanotechnology, medicine as well as environmental engineering. The MOFs have been shown to be promising as materials for gas storage and separation, sensors, ferroelectric and non-linear optical materials, magnetism, catalysis, drug delivery etc and researchers have been devising strategies to utilize the MOFs to tackle a number of global challenges of the twenty-first century. A survey of the literature reveals that the linear organic linkers, 1,4- benzenedicarboxylic acid (BDC) and 4,4’-biphenyldicarboxylic acid (BPDC), have been the organic linkers of choice for the construction of stable, porous and multifunctional MOFs. The aim of this thesis has been to monitor the effect that the presence of a functional group in between the benzene rings of the BPDC would have on the overall structures and the properties of the MOFs. Thus, as part of the investigations, the preparation of the MOF compounds using 4,4’-sulfonyldibenzoic acid (SDBA) and 4,4’- azodibenzoic acid (ABA) have been accomplished. Along with the conventional hydrothermal and solvothermal synthetic techniques, the liquid-liquid biphasic reaction method was also utilized for the synthesis of some of the compounds. The structures of the compounds were ascertained from single crystal X-ray diffraction technique. Proton conductivity studies were performed on Mn based porous MOFs using AC impedance spectroscopy. The ferroelectric behavior in a Co based porous MOF was established using dielectric and polarization vs electric field measurements. The labile nature of the lattice solvent molecules was established utilizing single crystal X-ray diffraction studies and water sorption experiments. In addition, the site selective substitution in a homometallic MOF and the subsequent conversion to a mixed-metal spinel oxide upon thermal decomposition, have also been studied. Chapter 1 of the thesis is a brief overview of the metal organic framework compounds and summarizes the various important structures that have been reported in literature and the interesting properties that they exhibit. In chapter 2, the proton conductivity behavior, solvent mediated single crystal to single crystal (SCSC) and related structural transformations in a family of Mn and Co based porous MOFs with SDBA have been presented. Also presented are the results of the site selective substitution of Mn by Co in a homometallic Mn based MOF and it’s subsequent decomposition to CoMn2O4 spinel oxide nanoparticles. In chapter 3, the syntheses, structures and the magnetic properties of the pentanuclear Mn5 based MOF compounds with SDBA have been presented. The role of the time and the temperature in the formation of the compounds has also been presented. In chapter 4, the dehydration/rehydration mediated switchable room temperature ferroelectric behavior, the single crystal to single crystal solvent exchange studies and selective gas sorption behavior in an anionic Co based MOF with SDBA has been discussed. In chapter 5, the use of the liquid-liquid biphasic synthetic route in the formation of Zn and Cd based MOFs with ABA has been discussed. Structural transformations between the one dimensional Zn based compounds and the heterogeneous catalytic studies using the Cd based compounds have also been presented.

The organic light-emitting diode (OLED) technology is emerging to be the future technology of choice for thin, flexible and efficient display and lighting panels and is a potential competitor for the existing flat panel display technologies, like liquid crystal display (LCD) and plasma display panel (PDP). OLEDs display is already making their way from both lab and industry research to display market and the pace of development of laboratory OLED design into a commercial product is very impressive. The OLED display offers several advantages over other display technologies, such as low power consumption, easy fabrication, high brightness & resolution, light weight, compact, flexible, wide viewing angle and fast response. However, OLED display is still in amateur stage in terms of their cost and lifetime. Despite of the abovementioned advantages of OLEDs, there still several issues that need to be addressed to explore the full potential of this display technology. The development of materials with high photoluminescence quantum yield (PLQY), thermal and electrochemical stability, packaging, and light extracting technology are some of the major issues. Among the emitting materials, the achievement of robust blue emitting material with high PLQY and color purity is still a challenge due to its intrinsic wide bandgap and complex device configuration. The work presented in this thesis is devoted to the development of robust blue emitting materials based on fluoranthene derivatives. Fluoranthene unit has been chosen due to its blue emission, high photoluminescence quantum yield, thermal and electrochemical stability. The thesis is organized in six chapters, and a brief discussion on the content of individual chapters is provided below. Chapter 1 provides a short description of evolution of display technology and history of OLEDs. The generation wise development of emitting materials for white OLED is concisely illustrated. The working principle, function of individual layer and factors governing external quantum efficiency of OLED device are elaborated. Finally, the important prerequisite properties of blue emitting materials for OLED application are outlined. Chapter 2 reports the design and synthesis of symmetrically and asymmetrically functionalized fluoranthene-based materials to address the issue of PL quenching in solid state, and subsequently for application in non-doped electoluminescent devices. A detailed experimental and theoretical study has been performed to understand the effect of symmetric and asymmetric functional groups on optical, thermal and electrochemical properties. The fluoranthene derivatives reported in this chapter exibited deep blue emission with high PLQY in both solution and solid state. The vacuum deposited non- doped OLED devices were fabricated and characterized utilizing these materials as emitting layer. Chapter 3 describes the rationale design of thermally stable fluoranthene derivatives as electron transport materials for OLEDs. The two derivatives investigated in this chapter comprised of two fluoranthene units linked by diphenylsulfane and dibenzothiophene linkage. The effect of rigidity provided by ring closure in molecular structure on the physical and charge transport properties has been investigated. Such materials are urgently demanded for better performance and durability of displays. In an extension to chapter 3, fluoranthene based dual functional materials possessing blue light emission and electron transport characteristics are described in Chapter 4. The application of these materials in bilayer blue OLED device successfully demonstrated. The development of such dual functional materials is an important step to not just simplify the OLED device architecture; but also has the potential to reduce the manufacturing and processing cost significantly. Chapter 5 reports the synthesis of the star-shaped fluoranthene-triazine based blue photoluminescent materials for solution processable OLEDs. The effect of chalcogen on the photophysical and electroluminescence properties has been investigated. The main advantage of such solution processable materials over small molecules is to overcome the power consuming vacuum thermal evaporation technique for deposition. Chapter 6 describes the design and synthesis of a new blue emitting material comprising of a donor moiety and an acceptor unit to observe thermally activated delayed fluorescence (TADF). However, photophysical studies did not show any sign of delayed fluorescence in this molecule. Nevertheless, a deep blue electroluminescence is achieved using a multilayer OLED device configuration.