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ELECTRONIC STRUCTURE OF NOVEL MAGNETIC SYSTEMS
Full text linkThe present thesis is devoted to the study of low dimensional quantum spin systems and
low dimensional systems that exhibit multiferroic behavior.
Using ab initio density functional theory we have studied the electronic and magnetic properties
of a spin gap compound Sr2Cu(BO3)2. We have calculated the hopping and exchange
interactions between various Cu ions and derived the low energy spin model for the system.
The spin model turns out to be a system of decoupled spin ladders with strong rung coupling.
The validity of the model is checked by calculating the magnetic susceptibility as a function
of temperature and magnetization as a function of temperature as well as magnetic field using
Quantum Monte Carlo technique and comparison of the calculated results with the available
experimental data. Our results suggest that the above model is appropriate to describe the low
energy physics of Sr2Cu(BO3)2.
We have studied the electronic structure and magnetic properties of frustrated quantum
spin systems which include diamond chain antiferromagnets Ba3Cu3X4O12 (X = Sc, In) and
also the proposed staircase Kagome lattice system PbCu3TeO7. With the aid of first principles
calculations we have identified the dominant exchange paths of these systems which are not
obvious from structural considerations. Our estimation for the Curie-Wiess temperature from the computed exchange interactions compares well with experiments. The calculated exchange couplings lead to long range magnetic order, in contrast to the expectation from the structural considerations. Using first principles density functional calculations, we have studied the electronic structure of the low dimensional multiferroic compound FeTe2O5Br to investigate the origin of
magnetoelectric (ME) effect and the role of Te ions in this system. We find that without magnetism even in the presence of Te 5s lone pairs, the system remains centrosymmetric due to the antipolar orientation of the lone pairs. Our study shows that the exchange striction within the Fe tetramers as well as between them is responsible for the magnetoelectric (ME) effect in FeTe2O5Br. We also find that the Te4+ ions play an important role in the inter tetramer exchange striction as well as contribute to the electric polarization in FeTe2O5Br, once the polarization is triggered by the magnetic ordering. Finally we have studied the magnetic and ferroelectric properties of two dimensional triangular
lattice antiferromagnetic AgFeO2 and compared with the isostructural system CuFeO2. Our calculations reveal spin orbit coupling has a profound effect on the magnetic and ferroelectric
properties of AgFeO2. Calculations of ferroelectric polarization suggest that the spontaneous polarization arises from noncollinear spin arrangement via spin orbit coupling. Our calculations also indicate that in addition to electronic contribution, the lattice mediated contribution to the polarization are also important for AgFeO2.The research was conducted under the supervision of Prof. Indra Dasgupta of the Solid State Physics division under SPS [ School of Physical Sciences]The research was carried out under sponsorship Council of Scientific and Industrial Research (CSIR) (Grant No.09/080(0615)/2008-EMR -1) for research fellowship, financial support from MONAMI and infrastructural support from IACS
Study of Structural and Electrical Properties of Cathode Materials and Glassy Electrolytes
Full text linkThis thesis deals with the synthesis of some cathode materials and glassy electrolytes
and their characterization using several techniques such as differential scanning calorimetry
(DSC), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM),
transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR)
studies etc. as well as electrical measurements in wide frequency and temperature range. The
thesis is organized as follows:
Chapter 1 presents an introduction to cathode materials and glassy electrolytes along
with some precise definitions in this context. Secondly, it presents different models of ac and
dc conduction in ion conducting and electron conducting systems. Finally, it presents precise
objectives of the present work.
Chapter 2 presents the sample preparation techniques as well as different
experimental techniques such as X-Ray Diffraction (XRD), Field Emission Scanning
Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Differential
Scanning Calorimetry (DSC), Fourier Transform Infrared (FT-IR) Spectroscopy, electrical
and dielectric measurements etc.
In chapter 3 the micro-structural properties of the cathode compound
Lix(Mn1/3Ni1/3Co1/3)O2- (x=1, 0.9 and =0, 0.05) has been studied. This compound has been
prepared in solid state synthesis route using a wide range of calcination temperatures. The
post-calcination heat-treatment has been employed in all the samples. The effect of
calcination temperature and heat treatment on the microstructure and morphology of this
compound has been studied in details. The synthesis condition of the compound has been
optimized by the combination of calcinations and heat-treatment.
In chapter 4 the electrical properties of the electrode compounds
Li[Ni1/3Mn1/3Co1/3]O2 and Li0.9[Ni1/3Mn1/3Co1/3]O1.95 have been investigated in a wide
temperature and frequency range. The temperature dependence of the dc conductivity has
been explained employing polaron hopping models, proposed by Schnakenberg and Emin
and co-workers, which consider the coupling of polarons with optical and acoustic phonon modes. The experimental ac conductivity data have been analyzed in the framework of several theoretical models based on quantum mechanical tunneling and classical hopping
over barriers. It has been shown that the electron tunneling is dominant in the compositions in the temperature range from 93 K to 193 K. A crossover of relaxation mechanism from electron tunneling to polaron tunneling is observed at 193 K.
In chapter 5 the structural and electrical properties of CdI2 doped silver polyphosphate, meta-phosphate and ultra-phosphate glassy electrolytes have been investigated. Xray diffraction, scanning and transmission electron microscopic study has been performed to investigate the presence of crystalline phases within the glassy matrix. The identification of
different crystalline phases has been performed by analyzing the selected area electron
diffraction (SAED) patterns. Electrical properties of the compositions have been investigated
in a wide temperature and frequency range. The electrical data have been analyzed in the
framework of the conductivity and the modulus formalisms. It has been shown that the
increase or decrease of the conductivity in these glasses depends on the degree of Cd-Ag
exchange.
In chapter 6 the mixed glass former effect has been investigated in silver borophosphate
glassy electrolytes. The micro-structural study of the compositions has been
performed by employing different experimental techniques such as XRD, SEM, TEM, DSC
etc. The network structure of the glassy electrolytes has been analyzed from FTIR spectra.
The population of BO4 and BO3 units in these compositions has been determined from
deconvolution of FTIR spectra. Electrical properties of the compositions have been
investigated in a wide temperature and frequency range. The experimental data have been
analyzed in the framework of conductivity and modulus formalism. Two different types of
microscopic length scales of ion dynamics such as characteristic length scale and spatial
extent of ion motion have been estimated from linear response theory. It has been shown that
the dc conductivity and microscopic length scales of ion motion are strongly correlated to the
population of BO4 and BO3 units.
In chapter 7 two different phenomena have been investigated. First one is
mixed glass former effect in silver boro-phosphate glassy electrolytes in presence of a dopant
CdI2. The second one is immobile salt effect in CdI2 doped silver boro-phosphate glassy
electrolytes. The micro-structural study of the compositions has been performed by
employing different experimental techniques such as XRD, SEM, TEM, DSC etc. The
network structure of the glasses has been analyzed from FTIR spectra. Electrical properties of
the compositions have been investigated in a wide temperature and frequency range. The
experimental data have been analyzed in the framework of conductivity and modulus
formalism. It has been observed that different physical properties such as dc conductivity,
glass transition temperature, density etc. are different in CdI2 doped borophosphate glassy electrolytes from that for undoped borophosphate glassy electrolytes. It has been shown that the mixed former effect and immobile salt effect are correlated to each other.The research was conducted under the supervision of Prof. Aswini Ghosh of the Solid State Physics division under SPS [School of Physical Sciences]The research was carried out under the RCI (DRDO) and DST Gran
Photophysical Studies of some Organic Molecules and their Modification in some Restricted Organized Assemblies and Heterogeneous Media
Full text linkThe study has been done for the investigations on the photophysical characteristics of organic moleculecules and the effect of different organized media and environmental conditions on its photophysical dynamics by analyzing their steady state and time-resolved spectroscopic method. Some theoretical calculations have also been done to substantiate the experimental findings. All the studies have been carried out under the supervision of Professor Sankar Chakravorti in the Department of spectroscopy, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032, India. The thesis contains eight chapters and two appendices. Chapter 1 contains the introduction and a brief review of the existing knowledge to the present work and outline of the purpose and problems studied in the present investigation. Second chapter contains a description of the experimental techniques, materials, methods and theoretical calculation used. Chapter 3-8 contain photochemical and photophysical properties of 1,8 naphthalimide (NAPMD) in different media.
Most of the results incorporated in this thesis have been published in referred international scientific journals, a list of which is appeared at the end of this dissertation.The research was conducted under the supervision of Prof. Sankar Chakraborty of the Spectroscopy division under SPS [School of Physical Sciences]The research was carried out under IACS fellowship and DST research gran
Theoretical study of structure, dissociation, reaction and thermochemistry of molecules of environmental and industrial interest
No full textThe present dissertation entitled “Theoretical study of structure, dissociation, reaction and
thermochemistry of molecules of environmental and industrial interest” is submitted to
fulfill the requirements for the degree of Doctor of Philosophy (Science) of Jadavpur
University. The study has been done for the investigation of electronic structure, metal
ligand coordination, potential energy surface of reaction and thermochemistry of molecules
having environmental and industrial interest using high-level theoretical methods. This thesis contains five chapters. An introduction of the thesis is given in first chapter for
understanding the environment and industrial chemistry. The second chapter describes briefly the computational science, computational chemistry and a review of the theoretical methods. Third chapter deals with the electronic structure and metal ligand coordination observed in some chelates. The fourth chapter gives a theoretical account of the study of the reaction mechanism of an interesting atmospheric reaction. The dissociation channels, thermochemistry and spectroscopy of some molecules of industrial and atmospheric interest are studied in detail in last chapter five.The research was carried out under supervision of Prof. Abhijit Kr. Das of the Spectroscopy division of the SPS [School of Physical Sciences
Optical Properties of Metal and Semiconductor Nanostructures
Full text linkThe optical properties of the semiconductor nanostructures are dominated by emission of electrons excited by incidental photon. However, impurities or defects can modify the band structure of the semiconducting nanocrystals, there by, affecting the optical properties of nanocrystals. The work presented in this thesis describes plasma excitation in metal nanostructures as well as emission properties of semiconductor nanocrystals synthesized in hydrothermal route.The research was conducted under the supervision of Prof. S K Saha of the Materials Science division under SMS [School of Materials Science]The research was carried out under CSIR research fellowship and research gran
Fluorescent Bioimaging Probe from Aggregation Induced Emission Active Molecule
No full textThe research was conducted under the supervision of Prof. N R Jana of the SMS [School of Materials Sciences]The research was carried out under CSIR research fellowshi
Functionalized Nanoparticles and Quantum Dot as Cellular Imaging Probe
No full textThe research was conducted under the supervision of Prof. N R Jana of the SMS [School of Materials Sciences]The research was carried out under DST fellowshi
Detection and Inhibition of Amyloid Fibrillation using Functional Molecules and Nanoparticles
No full textThe research was conducted under DST fellowshipThe research was carried out under the supervision of Prof. N R Jana of SMS [School of Materials Sciences
Probing Aromaticity in Intermediate and Transition States along with Non-Traditional Reaction Paths
Full text linkFor chemists, the tryst with aromaticity began with the dream and subsequent works
by Kekule. Gradually with the advent of quantum chemistry, aromaticity was given a
strong theoretical foundation, the Huckel's rule being the most prominent of them.
Yet the problem of quantification of aromaticity remained unresolved. This problem
was interfaced with the phenomenon of magnetically induced ring current and
quantification of aromaticity was linked with NMR chemical shifts. Nuclear
Independent Chemical Shift (NICS methods) and more recently Magnetically
Induced ring Current density (MICD) have been used to quantify aromaticity. NICS
has been employed majorly, due to its computational simplicity, to investigate the
implication of aromaticity in chemical reactions, by quantifying aromaticity of
transition states, in pericyclic reaction in particular. MICD has seen some very few
recent applications. Chances for isolation of transition states are nil and aromaticity
of intermediates of chemical reactions have rarely been investigated. The work
presented in this thesis is concerned with the investigation of aromaticity property
for intermediates involved in the non-traditional mechanistic pathways of simple
chemical reactions. This thesis is composed _of two major types of work/findings.
Firstly the attempt has been to establish unusual mechanistic pathways for simple
chemical reactions. This thesis reconciles different facets of quantum chemistry like
static computation, for structure determination and property calculation, coupled
with the reaction dynamics, in condensed phase, under one common roof. Secondly,
computation and quantification of aromaticity, using NICS and MICD in particular,
for intermediates along the non-traditional reaction paths has been addressed. The
chemical reactions investigated span from oxidation reaction and photo-redox
process to excited state photochemical reaction. Four-center-two-electron (4c-2e) bond is a more recently discovered bonding
pattern. Aromaticity of paradigmatic cases of 4c-2e bond like TCNE2 (2-) and foursulfur- two-electron bonded complex have been thoroughly investigated. An unusual 4c-2e bonded intermediate has been found in the mechanistic pathway for oxidation of hydrazine. The aromaticity of this intermediate has also been investigated. Excited state aromaticity has been addressed using MICD technique for the first time. While investigating the photo-dissociation of N2 from 5-Phenyl- Tetrazole, an interlink between photo-induced charge transfer and drastic changes in excited-state aromaticity has been established.
Additionally, a prebiotic photo-redox reaction has been studied. Dimerization of two dipole-bound-anions was found to be a crucial step in the mechanism for the photoreduction process. Despite the coulombic repulsion, the dimerization was found to be facile due to the gain in the aromatic stabilization of the dianionic intermediate formed.Research was carried out under the supervision of Prof. Ankan Paul of RCAMOS under SCS [School of Chemical Sciences]Research conducted under CSIR fellowship research gran
Design, Synthesis and Biological Applications of Modified Morpholino Nucleosides
Full text linkThe work embodied in this thesis entitled “Design, Synthesis and Biological Applications of
Modified Morpholino Nucleosides” was initiated by the author in February, 2008 in the
Department of Organic Chemistry, Indian Association for the Cultivation of Science, Kolkata
under the supervision of Dr. Surajit Sinha.
In Chapter 1, a general introduction of the antisense oligonucleotide field has been
presented. The important members and major challenges of antisense oligos have been briefly
discussed.
In Chapter 2‐Part A, development of a considerably improved protocol for the synthesis
of flexibly protected 7´‐hydroxy morpholino nucleoside monomers has been described. In
Chapter 2‐Part B, a new methodology for the deprotection of trityl amines, which are frequency
encountered in morpholino chemistry, has been presented.
In Chapter 3‐Part A, synthesis of a guanidinium‐linked morpholino (GMO) pentamer
has been presented. Fluorescent version of the GMO has also been prepared. In Chapter 3‐Part
B, a new, mild and high yielding protocol for the synthesis of 7´‐chlorophosphoramidateactivated
morpholino monomers has been described. Taking the help of the developed
methodologies, a new type of photo‐caged morpholino oligomer has been synthesized.
In Chapter 4, the fluorescent GMO prepared in Chapter 3‐Part A has been successfully
tested in cell culture for its cellular transfection property. Encouraged by the results, the GMO was conjugated with Gli 1‐targeted morpholino antisense by click chemistry and a preliminary study on luciferase based hedgehog inhibition assay was also performed. Attention has been given to incorporate all the current references related to this contemporary area of research.Research was taken care under the supervision of Prof. Surajit Sinha of the Organic Chemistry division under SCS [School of Chemical Sciences]Research was carried out under CSIR fellowshi