PhD Theses (Chemistry)

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    Computational investigation of excited state processes in ESIPT-based systems and vinylene-linked thiophene pyrrole
    (2024) Mawa, Ibanrishisha
    The thesis focuses on understanding the mechanistic pathway in systems undergoing excited state intramolecular proton transfer and cis-trans isomerization. Unveiling the mechanism of these processes at an atomistic scale is of utmost importance as it would add to our understanding and assist in designing materials with better performance. These kinds of processes are observed in our everyday life such as the vision process in retinal chromophores, vitamin D production in humans on exposure to sunlight and mutation during DNA replication, etc. The application part of systems undergoing photoinduced processes are realized in the design and development of certain materials such as optoelectronic devices. The thesis has three working chapters. The first work is based on 1-hydroxy-2-acetonaphthone (HAN) due to the unsettled issues regarding the proton transfer process. In addition, the process of full photocycle including the non-radiative relaxation pathways is proposed. The second work highlights the effect of implicit solvents on the photoinduced processes in nitrile-substituted 2-(oxazolinyl)-phenols. Additionally, the mechanisms behind these two regiomers’ weakly emissive properties in the solvent phases are investigated. My last work involves the exploration of photoisomerization pathways in vinylene-linked thiophene-pyrrole system. Considering the computational cost for the dynamics study in the excited state, we have employed single-reference method such as time-dependent density functional theory (TDDFT) and algebraic diagrammatic construction scheme of second order (ADC(2)). However, multi-reference studies are also incorporated in our study wherever the single-reference methods fail.
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    Properties and Potential Applications of Biomimetic and Bio-derived Nanofluidic Systems
    (2021) Konch, Tukhar Jyoti
    The branch of fluid dynamic that explore the flow of liquid in structure constrained to nanometer size regime (1-100nm) is defined as nanofluidic. Fluidic transport in and around nanofluidic structures is dominated by interactions of otherwise weak effects such as the formation of electrical double layers (EDL), attractive or repulsive forces of charged species, and entropic barriers. Typically, transport of charged species through nanometer-sized channels are dominated by the overlapping electrical double layers. One of the major difficulties in designing nanofluidic devices is the inherent complexity. The overall transport characteristics are determined by the interplay of various nanoscale or even molecular level physical, geometric, and chemical factors. Biological ion channels, however, are known for their capability of elaborately manipulating these factors to regulate the transmembrane ionic flow, which plays a crucial role in a number of physiological processes. Mimicking the biological systems researchers has tried to demonstrate its artificial counterparts. In light of this feature, various ion-channel-mimetic smart 1D nanofluidic systems have been developed that can reproduce functions analogous to its parent biological systems. Although systematic research in single-pore devices makes the physical picture of this nanofluidic process much clear, it is still far from competent for practical applications. Toward practical applications, one major challenge is to extrapolate individual nanofluidic devices to macroscopic platform in a cost-efficient way. Interestingly solution to the above mentioned dilemma was also resolved from natural inspirations in the form of lamellar microstructure of nacre, in which soft materials (polysaccharides and proteins) are sandwiched between hard inorganic layers (aragonite platelets), forming an alternatively arranged layered structure. This novel method of material designing and large-scale integration of individual artificial nanofluidic channels into a macroscopic platform give birth a new research filed known as the 2D nanofluidics. Via a simple vacuum filtration process, colloidal dispersions of individual 2D nanosheets can be reassembled into a densely stacked multi-layered structure. The interstitial space between opposite 2D nanosheets can be treated as lamellar channels for mass and charge transport.
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    Transition-Metal Catalyzed Regioselective C-C/C-Heteroatom Bond Formations: Access to Functionalized Arenes and Heterocycles
    (2022) Sarkar, Tanumay
    The thesis is divided into four chapters. The first chapter illustrates a Ru(II)-catalyzed siteselective C-H acyloxylation of N-aryl-2-pyrimidines with carboxylic acids as the acyl source. The second chapter describes a Ni(II)-catalyzed oxidative C-H heteroarylation of arenes with azoles utilizing a removable oxazoline-based directing auxiliary. The third chapter deals with the Bi(III)- catalyzed annulation of 2-naphthols with N-sulfonylaziridines. The fourth chapter demonstrates (3+3)-cycloaddition of aziridines with diaziridines for the stereospecific synthesis of triazines under Fe(III)-catalysis.
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    Ipso Nucleophilic Substitution on Electron Deficient Arene Systems
    (2024) Mondal, Sandip
    The thesis entitled, “Ipso Nucleophilic Substitution on Electron Deficient Arene Systems” mainly focused on the development of greener and transition metal free methodologies for various alkylation reactions. The contents of the thesis have been divided into five chapters based on the results of experimental works performed during the research period.
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    Design of Coatings Embedded with Tolerant, Tailored and Responsive Underwater Oil Wettability and Oil Adhesion
    (2023) Borbora, Angana
    The anti-oil wettability of various naturally existing underwater creatures has inspired researchers to develop artificial super oil repellent interfaces for multiple applications in engineering, healthcare, and environmental remediation. In the past, several approaches were adopted to artificially fabricate underwater oil-repellent surfaces, formally known as underwater superoleophobicity, by co-optimizing hydrophilic chemical composition and rough micro/nano-structures on their surface. However, the earlier reported approaches in deriving underwater superoleophobicity were unable to associate some other essential properties, such as, physical and chemical durability, adaptive tuning of oil adhesion, and transparency in the prepared surfaces. Here, a facile 1, 4-conjugate addition reaction is exploited to derive covalently crosslinked chemically reactive coatings on various surfaces loaded with residual chemical functionalities that provide the opportunity to embed underwater superoleophobicity through appropriate post-covalent modifications. While the covalent crosslinking tailored mechanical property, the adequate chemical post-modification customized oil adhesion and optical transparency. The thesis entitled “Design of Coatings Embedded with Tolerant, Tailored and Responsive Underwater Oil Wettability and Oil Adhesion” is presented in six chapters. Chapter 1 introduces bio-mimicked underwater superoleophobic surfaces, the existing challenges associated with conventional artificial fabrication approaches, and the objectives of the thesis work. Chapter 2 demonstrates the fabrication of a dually reactive multilayer coating following the 1, 4-conjugate addition reaction and the post-covalent modification of the multilayer coating to immobilize highly sensitive bare micro-meter sized nematic liquid crystal (LC) droplets underwater for single LC droplet based repetitive sensing application. Chapter 3 accounts for the utilization of the dually reactive multilayer coating to develop various responsive underwater superoleophobic surfaces via post-modifications and their adaptive oil adhesion for sensing different amphiphilic (cationic, anionic and facial) molecules. Chapter 4 demonstrates the rational functionalization of the dual reactive multilayer coating to depict the highly selective raising of the oil contact angle (OCA) and rolling of a beaded oil droplet underwater in the presence of targeted and relevant toxic chemicals. Chapter 5 introduces a covalently crosslinked and chemically reactive sol-gel conversion process through the 1, 4-conjugate addition reaction to achieve a substrate-independent, mechanically durable, and optical transparent coating embedded with underwater superoleophobicity. Moreover, this approach allows to modulate mechanical property of highly deformable objects. Chapter 6 provides a brief summary and the future outlook of the work presented here.
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    (A) Computational Study of human Islet Amyloid Polypeptide Aggregation and its Inhibition
    (2023) Roy, Rituparna
    The aggregation of human islet amyloid polypeptide (hIAPP) stands at the nexus of Type II Diabetes (T2D) pathogenesis. In order to counteract the advancement of this disease, a possible therapeutic avenue is to curb the misfolding and aggregation of hIAPP. Within this thesis, we embark on the intricate journey of hIAPP aggregation, coupled with the myriad classes of compounds harboring the potential to impede this process. In Chapter I, a foundation is laid through the introduction of hIAPP and an array of different categories of inhibitors, each contributing to the modulation of hIAPP aggregation. A brief discussion of the molecular dynamics simulation methodology, which is a vital framework underpinning our study is followed. Thereafter, Chapter II takes the helm into venturing the different conformational states of an amyloid prone fragment of hIAPP, hIAPP20-29, via Markov State Modelling. Here, the transition pathway between the metastable states is analysed, which are crucial for the misfolding of hIAPP. Chapter III explores the influence of two small biological molecules on hIAPP aggregation. In Part (a), we have explored the effect of norepinephrine, which is a common neurotransmitter, on the amyloidogenesis of hIAPP. In Part (b), a new aspect of adenosine triphosphate (ATP), other than being the energy source for biochemical processes, is inquired. This chapter, thus, enlighten us about the diversity of the molecular structures that can modulate the aggregation of hIAPP and the effect of these structures on the activity of the inhibitors. Chapter IV turns the discourse towards peptides and peptidomimetics, probing their roles in shaping the aggregation narrative. Two such inhibitors are investigated, both of which are extracted from the amyloid core region of hIAPP, i.e., N22FGAIL27. In Part (a), this hIAPP fragment is replaced with all D-amino acids, and is used to prohibit the self-assembly of full-length hIAPP. In Part (b), a conformationally restricted element, aminobenzoic acid is incorporated into NFGAIL, by replacing Ile26 and/or Gly24 residues. Here, three different isomers of aminobenzoic acid is used, i.e., (β, γ, δ). β- and γ- containing peptidomimetics successfully prevent the aggregation of hIAPP, but δ- peptidomimetics promote it, highlighting the contrasting behaviour of the isomers. Hence, in this chapter, we have conveyed the effect of stereochemistry of the amino acid residues or modified organic moieties on the inhibitory potential of peptides or peptidomimetics. A novel dimension unfurls in Chapter V, where the alliance between boron nitride nanomaterials and hIAPP aggregation is explored. The curvature of the nanomaterials is observed to have an impact on their interaction site with hIAPP. Finally, Chapter VI unfurls a tapestry of conclusions, weaving together the diverse threads from our journey. In unity, this thesis stands as an ardent exploration, deciphering the aggregation pathway of hIAPP and unveiling a constellation of agents poised to intervene. The information regarding the structure and activity of the various inhibitors provides a holistic comprehension of the crucial molecular scaffolds and properties required to design drugs for combatting T2D's relentless advance.
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    Effect of the Position of Geminal Di-Substitution of g Amino Acid Residues on their Conformational Preference
    (2023) Debnath, Swapna
    This thesis investigated the role germinal di-substitution at various backbone positions of the gamma amino acid residue on their conformational preferences. The thesis consists of 5 chapters. The first chapter describes the gamma amino acids and their conformations reported in the literature. Chapters 2-5 describe the investigations carried out in this thesis, which includes the incorporation of gamma amino acid residues (g2,2,g3,3 and g4,4) in the peptides. Chapter 2, describes the structures and assemblies in the solid and solution state of different derivatives of gamma amino acid residue. The structures and assemblies in the solid state are reported to be different for the three amino acid residues. The position of the backbone di-substitution is shown to drive the assembly in the solid state but not in solution. In the Chapter 3, three gamma amino acid residues were incorporated in all 􀀀 amino acid containing model helical peptide sequences (tri, hexa and nona petides) and compared their relative helical propensity. The C12 helical conformation diminished as: g4,4 g3,3 g2,2. Helices with a central 􀀀 amino acid residue was shown to adopt mixed 10/12 helices of both handedness (left and right) in both solid and in solution state. Nona peptides containing g3,3 and g2,2 amino acid residues adopted an unusual ambidextrous helical conformation in the solid and in solution state. The ambidextrous conformation was stabilized by a water mediated hydrogen bonding. Ambidexterity was not observed in the nona-peptide containing g4,4 amino acid residues, likely due to the absence of the key water molecule in the structures. Chapter 4 describes the propensity of these three amino acid residues in being able to nucleate an isolated expanded C12 B-turn motif. Chapter 5 studies the ability of these amino acid residues in nucleating 􀀀 hairpin conformation. Both C12 􀀀-turn and 􀀀-hairpin conformation was favoured by g3,3 and g4,4 favoured, whereas g2,2 failed to nucleate either of them due to unfavourable steric contacts. This thesis reported conformational preference of the three differently di-substituted 􀀀 amino acid residues, in the solution and in solid states by primarily using NMR, CD and X ray crystallography. In collaboration with the computational lab, ab initio calculations have also been done to understand the energetics of conformational preference. The conclusions are very well supported by experiments and computations. The thesis showed how a position of disubstitution (in the g amino acid backbone) determines its conformational preference by fine-tuning the energetics. The results are useful for peptidomimetics and rational design of peptides with various architectures.
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    Creating Life-like Transience in Synthetic Vesicles
    (2022) Das, Saurav
    The thesis "Creating Life-like Transience in Synthetic Vesicles" explores several techniques and approaches for imbuing life-like non-equilibrium features in synthetic vesicular systems and their potential biomimetic applications in laboratory settings.
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    Effect of Pyridine and Imidazole Functionality on Chiral Resolution, Solution Spin State and Electrochemistry within Ni (II) and Fe (II) Complexes
    (2022) Bhattacharya, Sounak
    This thesis work stems from our quest to find a simple way to recognize an enantiomer from a racemic mixture using coordination bond. To do that, we choose to use Ni (II)(high-spin) and Fe (II) (low-spin) complexes of chiral bidentate Schiff-base ligands. Observations on Fe (II) complexes led to finding complexes that show high- spin <--> low-spin transitions in solution. Digging deeper with more complexes along with a host of electrochemical and spectrometric tools, we ended up finding an intimate relationship between donor groups, redox potential, and spin-state. The effect of replacing pyridine with imidazole on redox and the spin-state properties discussed in the thesis is relevant to biomimetic chemistry. Imidazole group is a part of L- histidine amino acid, ubiquitous in metalloenzyme active sites. On the other hand, pyridine donor is typical in ligands related to biomimetic chemistry.
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    Selective C-H and C-C Bond Functionalization of Benzo-Fused N-Heteroaromatic Compounds
    (2022) Sarmah, Bikash Kumar
    The present thesis, entitled “Selective C-H and C-C Bond Functionalization of Benzo-Fused N-Heteroaromatic Compounds” is divided into five chapters based on the results obtained from the experimental works during the course of PhD research period.
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    Exploring the Potential of Homogeneous Ru-SNS/NNS Complexes and Heterogeneous Ru-Hydrotalcite in De(hydrogenative) Transformations
    (2023) Sardar, Bitan
    The contents of the present thesis entitled as “Exploring the Potential of Homogeneous Ru-SNS/NNS Complexes and Heterogeneous Ru-Hydrotalcite in De(hydrogenative) Transformations” have been divided into five chapters. The first chapter contains a brief literature study related to various de (hydrogenative transformations) and the last four chapters were based on the results achieved from the experimental works performed during the entire course of the PhD research program. Chapter 1 contains a brief introduction to the literature review of acceptorless dehydrogenation and borrowing hydrogen reaction of alcohols via homogeneous catalysis and heterogeneous catalysis. In 21st century, the rapid depletion of fossil fuels and growing environmental concerns urges chemists and chemical industries to search for alternative raw materials and to develop new methodologies to produce sustainable chemicals and important building blocks. In this regard, biomass-derived alcohols was found to be best candidate, as they are non-toxic in nature. Moreover, alcohols are considered renewable starting materials that can be used in organic synthesis for various organic transformations and the preparation of commodity chemicals. In this context, “acceptorless dehydrogenation (AD)” and “borrowing hydrogen (BH)” catalysis plays a key role. These approaches are sustainable because this process liberates water and in some cases (i.e., AD) molecular hydrogen as clean by-products. And, these types of reactions could be successfully performed by various types of homogeneous and heterogeneous catalysts.
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    Interaction and Synchronization of Spiral Waves in a Reaction-Diffusion System
    (2023) Kalita, Hrishikesh
    Over the past few decades, spirals have attracted a lot of interest. From a spinning galaxy to a swarm of honeybees, rotating spirals are widespread in nature. Their widespread presence in nature has made the study of spiral waves relevant across various disciplines. In physical systems like fluid flows, liquid crystals, galactic formations, etc., in biological systems like the heart, chicken retina, neocortex, slime mould, etc., in chemical systems like the Belousov-Zhabotinsky (BZ) reaction system, the Briggs-Rauscher reaction, some simple precipitation processes, the oxidation of CO on platinum surfaces, etc., scientists have observed and studied spiral waves. Despite these studies, the ambiguity of spiral waves has prevented scientists from developing a comprehensive hypothesis
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    Aggregation Aptitude in Rigid and Flexible Molecular Systems: Comparative Photophysical and Analytical Studies
    (2023) De, Sagnik
    This thesis elucidates the important consequences in comprehension of aggregation outlook of flexible and rigid frameworks and their response towards environmentally and biologically relevant analytes. L1-L3 is designed which shows a comparative aggregation aptitude with chain length variation in amphiphiles. The entire photophysical study on aggregation process is dealt with. Then, these synthesized amphiphiles are used in creating hydrophobic surfaces due to their inherent property of hydrophobicity. Additionally, the concept of Photoinduced Electron Transfer or PET is applied in the detection of nitro antibiotics via fluorescence quenching. This chemo sensing is probed in biofluids viz; simulated gastric and body fluid. Next, a layout is provided where a comparative study between an amphiphile and a non-amphiphile is presented. The compounds designed and synthesized were substituted urea and amide (L4 & L5). Studies on aggregation-induced emission are shown by a binary solvent system DMF-Water. Morphological change is depicted on solvent switching by electronic microscopy imaging. Both solid and solution state emissive property is described. A unique photophysical prospect is shown in this piece of work i.e., light harvesting. Förster resonance energy transfer or FRET mechanism delivers the basis for this light-harvesting phenomenon between the amphiphile and a commercial dye; Rhodamine. Again, PET is applied to detect nitro explosives in water is demonstrated. This detection proceeds via disaggregation of the aggregated state. In the allied chapter, functionalization of amphiphile was done: a comparative outline on substituted urea and thiourea (L4 & L6). Apart from describing aggregational features through spectroscopy and microscopy, an edge on the chemo-sensing property is done. The thiourea selectively recognizes Hg (II) ions in an aqueous solution due to the soft-soft interaction between the sulfur atom and the heavy metal. Turn-On or fluorescence emission enhancement is achieved even in the presence of heavy metal during the chemosensing process. The toxic metal ion interaction causes disaggregation of the aggregated amphiphile confirmed through DLS and FESEM experiments. The chemo-sensing experiments are done in various real samples. Moreover, The Hg(II)-amphiphile ensemble detects sulfide ions in the water among all other sulfur-containing anions and amino acids.
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    Reactivity Studies of 4-Hydroxydithiocoumarin: Design & Synthesis of Novel Bioactive Molecules
    (2022) Mondal, Santa
    The thesis entitled “Reactivity Studies of 4-Hydroxydithiocoumarin: Design & Synthesis of Novel Bioactive Molecules” has been compiled into six chapters based on the experimental results and findings carried out by me during the entire research period. Chapter 1 provides a brief overview of organosulfur compounds and their importance. In addition, the reason for choosing 4-hydroxydithiocoumarin as the key starting material for the synthesis of novel bioactive molecules. Chapter 2 elaborates on the synthesis of 3-sulfenyl derivatives. Chapter 3 describes the synthesis of α-thiocarbonyl compounds. Chapter 4 illustrates the synthesis of vinyl sulfides and thioethers. Chapter 5 demonstrates the synthesis of 1,4-oxathiin derivatives. Chapter 6 elucidates the synthesis of β-hydroxysulfides and β-aminosulfides by ring-opening reactions.
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    Nitrosyl complexes of Co(II) and Mn(II) porphyrins - Reactivity towards reactive oxygen species and utility as HNO donor
    (2022) Mazumdar, Rakesh
    This thesis broadly covers our endeavor to comprehend some interesting reactivity of nitrosyl complexes of Co(II) and Mn(II) porphyrinates. A series of these complexes were synthesized by varying the substitutions at the meso positions of the porphyrin ring (e.g. phenyl, pentafluorophenyl and 4-methoxyphenyl) and central metal ion (e.g. Co2+ and Mn2+). The reactivity of these complexes towards reduced oxygen species (O2− and O22−) was explored following an attempt to mimic the mechanism of the nitric oxide dioxygenase (NOD) enzyme, which has been discussed in the chapters 2 to 4. In every instance formation of a putative PN intermediate was observed. Tedious efforts to identify and characterize the associated intermediates that form during its formation and decomposition led to some significant findings. For instance, in chapter 2, the formation of a [CoII(NO)(O2−)] species was evidenced spectroscopically prior to the formation of a [Co(II)-PN] intermediate. In chapter 3, a Co(III) porphyrin cation radical species has been detected in the decomposition of a [Co(III)-PN], which in turn confirms the involvement of a [Co(IV)=O] intermediate in the reaction. In chapter 4, we could prove the involvement of [Mn(IV)=O] in the decomposition of an [Mn(III)-PN] intermediate both spectroscopically and chemically. A [MnIII(NO)(O2−)] species was also observed prior to the formation of the [Mn(III)-PN]. We believe that these findings will contribute crucially to our existing knowledge of NOD chemistry and extensively to the field of metalloenzyme chemistry. However, despite our best efforts, the characterization of the PN complex itself was not very successful because of its highly unstable nature.
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    Newer Synthetic Approaches for the Disubstituted Quinolines from Aryl Amines
    (2022) Ali, Saghir
    The thesis entitled “Newer Synthetic Approaches for the Disubstituted Quinolines from Aryl Amines” describes the synthesis of 2,3- and 2,4-disubstituted quinoline derivatives. The thesis has been divided into three chapters based on the adept experimental results, which were carried out during the entire research period. Chapter II has been subdivided into three parts A, B and C. Chapter III has also been subdivided into part A and B. Chapter 1 conveys a brief introduction to disubstituted quinolines and its importance. Chapter 2 reports the synthesis of 2,3-disubstituted quinolines. Part A describes the synthesis of 2,3-dialkylquinolines. Part B explains the synthesis of 2-benzyl-3-phenylquinolines. Part C discusses the synthesis of 2,3-diarylquinolines. Chapter 3 describes the synthesis of 2,4-disubstituted quinolines. Part A illustrates the synthesis of quinoline-2,4-dicarboxylates. Part B explains the synthesis of 2-benzyl-4-phenylquinolines
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    Development of New Therapeutic Materials for Mitigation of Amyloid Neurotoxicity Associated with Alzheimer’s Disease
    (2022) Mondal, Subrata
    Alzheimer’s disease (AD), an irreversible brain disorder, first diagnosed more than 100 years ago, still remains a curse to the society, affecting 30 million people worldwide, victimizing one in ten individuals above 65 years’ age, due to lack of efficient therapeutic strategy. Intense research activity suggests that amyloid fibrils originating from self-aggregation of amyloid β peptide having cross-β sheeted conformation are the hallmark of this disease. Hence, inhibition of amyloid aggregation can offer a platform to develop early stage therapeutics against several neurodegenerative diseases including AD.
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    Deriving Functional Interfaces from Chemically Reactive and Porous Dip Coating
    (2023) Das, Supriya
    Bioinspired liquid wettability and patterned interfaces remained an inspiration for developing various functional materials/interfaces for relevant and important applications. The essential criteria for contriving bio-inspired extremes of water wettability (either superhydrophobicity or superhydrophilicity) is the co-optimization of hierarchical topography and essential surface chemistry. In general, such optimization is artificially achieved following various top-down and bottom-up approaches, where various hydrophilic building blocks are associated using electrostatic interaction, hydrogen bonding, and other weak bonding (e.g., metal-thiol etc.), for developing the desired hierarchical features and optimizing the appropriate chemistry on top of this featured interface. However, such common and conventional designs are inappropriate for sustaining practically relentlessly harsh settings. So, further development for the synthesis of a durable and substrate-independent superhydrophobic coating is essential for various prospective applications in “real-world” scenarios. In this thesis, I have successfully accounted a simple and singlestep dip coating process to achieve a substrate- independent, chemically reactive, and porous polymeric coating following a 1,4-conjugate addition reaction at ambient conditions. Such chemically reactive polymeric dip coatings were further exploited for demonstrating pertinent applications, i.e., oil-water separation, self-cleaning, strain sensing, and anti-counterfeiting. The thesis entitled as “Deriving Functional Interfaces from Chemically Reactive and Porous Dip-Coating” has been codified in six chapters. Chapter 1 accounts for the introduction of bio-inspired liquid wettability and the discussion on the existing challenges related to durability, scalability and substrate independency. The potential utilization of prospective porous and chemically reactive coatings was also presented in this chapter. In Chapter 2, a simplistic approach of single step dip-coating technique is introduced to synthesize a substrateindependent and highly abrasion tolerant superhydrophobic coating. Further, the superhydrophobic coating on water soluble (sugar cube) substrate allowed the designing of a highly compressible and durable superhydrophobic sponge for the separation of crude oil-water mixture with an efficiency of > 99%. In Chapter 3, I have developed an abrasion tolerant superhydrophobic and conductive patterned interface for real-time and wireless monitoring of slow, fast, weak and strong human motions and expressions as well. The dip-coated porous polymeric interfaces were extended in Chapter 4, to develop a spatially selective chemically modulated patterned interface, where the strategic association of chemically modulated patterned wettability allowed to achieve a transient, and reversible visualization of hidden information with the naked eye. In Chapter 5, I have exploited the dual residual chemical reactivities of the prepared polymeric dip coating for developing an orthogonally readable, abrasion tolerant and miniaturized bulkpatterns through 1,4-conjugate addition reaction. Finally, in Chapter 6, summary of my entire thesis work has been elaborated and future prospects of the current design of chemically reactive dip coating are also provided.
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    Modulation of Ground and Excited State Dynamics in Donor-Acceptor Organic Functional Small Molecules for Photonics and Biomedical Applications
    (2023) Barman, Debasish
    Organic photofunctional materials based on donor-acceptor (D-A) π-conjugated structures with ambient stable triplet-harvesting thermally activated delayed fluorescence (TADF), room temperature phosphorescence (RTP) and aggregation induced emission (AIE) have received immense attention on gathering momentum and rapidly progressing towards commercial application. Successful design strategies of these combined properties are resulted in thermal up-conversion of non-emissive triplets into emissive singlet excitons, increasing the maximum internal efficiency from 25 to 100 % in purely organic systems. Throughout the course of this thesis, design and development of new organic D-A and D-σ-A based molecules with their intrinsic structure-property functions along with ground and excited state kinetics are precisely elucidated. The exciting photophysical properties of AIE, TADF and RTP activity and associated mechanism carefully investigated in different new class of single component to multicomponent binary systems (co-crystals) respectively. With the finding of novel chemical structures, few important photophysical mechanism was elucidated towards the origin of multimode emission and white-light emission with the current aspects of excited-state mechanism for model TADF involving of higher-order vibronic coupling and “hot-excitons”. In addition, complementary to TADF, RTP, another efficient triplet harvesting emitter has also been investigated for control release of excitons and to discriminate the individual and/or combined emission from TADF in a structurally rigid or flexible molecular skeleton. Besides, we could solved the dilemma of excited state quenching effect in aggregated or solid state by exploring Anti-Kasha mechanism as reason for AIE behavior. Moreover, it is discussed how to modulate and harvest the efficiency of the ambient triplets by varying different molecular conformers that show variant charge-transfer induced color-tunable emission, efficient photon transportation as optical wave-guiding activity in crystals and generation of toxic reactive oxygen species in aggregated state for image-guided cancer therapy.
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    Multifunctional Materials for Organic and Perovskite Solar Cells
    (2022) Garai, Rabindranath
    The ever-increasing energy demand is a burning question for the modern world as the conventional energy sources are finishing exponentially and cause severe environmental damage. Therefore, it is imperative to explore costeffective, and renewable energy sources. Solar energy is the most promising competitor of fossil fuels to overcome the present energy needs. Organic solar cells (OSCs) and perovskite solar cells (PSCs) have become one of the most important photovoltaic technologies in terms of efficiency. This thesis was focused on the material engineering of OSCs and PSCs. At first, the microwave synthesis of a well-known conjugated polymer PTB7-Th with high molecular weight and low dispersity was performed to fabricate highly efficient OSCs. A thorough investigation of optoelectronic property and device performance was demonstrated with respect to the structure-property relationship of polymers. Highest power conversion efficiency (PCE) of 8.47 % was obtained with insignificant batch to batch variation for the microwave synthesized polymer. After that, all the other works were based on the improving device efficiency and stability of PSCs by applying suitable passivation molecules. Primarily, the role of several multifunctional molecules on crystallization and grain growth of perovskite was investigate. Chelidamic acid (CA) revealed optimum trap passivation ability among all and the CA passivated film emonstrated improved film morphology and better crystallinity. As a result, a high PCE of 19.06% was attained along with enhanced thermal and long-term ambient stability. Afterward, a conjugated polyelectrolyte (PHIA) was used for perovskite passivation. The PHIA passivated device disclosed a high device efficiency along with outstanding stability in varied conditions. In the subsequent work, the effect of novel triple passivation technique was demonstrated which can simultaneously improve UV and ambient stabilization. The function of each passivation layer was studied carefully for a clear understanding. The triple passivated device exhibited outstanding UV and ambient stability as well as a high PCE of 20.46%. Finally, the fabrication of 2D-3D graded perovskite was demonstrated for improved efficiency and stability. A detailed analysis of the film morphology, trap passivation, device stability in the 2D-3D graded heterostructure was investigated meticulously. This 2D-3D graded perovskite resulted in a champion PCE of 21.18% with superior ambient stability. The efforts demonstrated in this thesis This thesis provides significant insights into the future commercialization of OSCs and PSCs.