Browsing by Author "Adhikari, A. Vasudeva"

Now showing 1 - 7 of 7

Design and Synthesis of New Donor-Acceptor Type Conjugated Polymers for Photonic Applications
(National Institute of Technology Karnataka, Surathkal, 2013) K. A., Vishnumurthy; Adhikari, A. Vasudeva
In recent years, a great deal of interest has been focused on the synthesis of novel D-A type conjugated polymers because of their excellent photonic properties. Recently, lots of attentions have been dedicated towards the development of new D-A type polymers with desired properties through proper structural modifications. In this context, the proposed research work has been aimed at design and synthesis of new D-A type conjugated polymers with improved photonic properties. Based on the literature review, five new series of D-A type conjugated polymers (P1-P20) carrying various electron donors and acceptor moieties have been designed. Seven series of bi-functional monomers required for the synthesis of new polymers have been prepared using appropriate synthetic procedures. Structures of new intermediates and monomers have been evidenced using spectral and elemental analyses. Starting from these monomers, five new series of target polymers, viz. (i) poly(3,4-ditetradecyloxythiophene)s carrying thiophene, naphthalene, isopthalyl, vinyl and pyrazole moieties as π-conjugated spacers (Series 1, P1-P5), (ii) poly(cyanopyridines) containing phenyl, carbazole, alkoxythiophene phenothiazine and dipenyl amine based electron donating bridges (Series 2, P6-P10), (iii) poly(3,4- ditetradecyloxythiophene)s involving vinylene π-conjugated spacers (Series 3, P11- P14), (iv) poly(3,4-ditetradecyloxythiophene)s carrying aromatic conjugated cyclic imides (Series 4, P15 and P16), and (v) poly(3,4-ditetradecyloxythiophene)s with imine functionalized electron donors as π-conjugated bridges (Series 5, P17-P20), have been successfully synthesized and their synthetic protocols have been established. Their structures have been confirmed by different spectroscopic and elemental analyses. Their molecular weights have been determined by GPC technique and thermal properties have been evaluated by TGA studies. Electrochemical properties have been studied using CV experiments. The linear optical characteristics have been estimated by UV-visible absorption and fluorescence emission spectroscopy. Their fluorescent quantum yields and solvatochromic behavior have been determined. Finally, their third-order NLO properties have been investigated using open aperture Z-scan technique to investigate their optical limiting behavior. Most of the polymers have exhibited promising results.
Molecular Design and Synthesis of New Cyanopyridone-Based Small Molecules for Oled Applications
(National Institute of Technology Karnataka, Surathkal, 2024) K S, Vishrutha; Adhikari, A. Vasudeva; Bhat, B. Ramachandra
In recent years, due to their widespread use in electronic devices like organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), organic light emitting transistors (OLETs), organic solid-state lasers, organic solar cells (OSCs) and biomedical devices, the development of efficient organic π-conjugated small molecules has been a vital part in the field of electronics. Essentially, these materials mainly stand out because of their well-organized molecular structures, simple synthetic methods, straightforward purification procedures, amenability to solution and vacuum deposition processing while fabrication, and the ability to fine-tune functional properties through relatively straightforward structural engineering. Over the past decade, due to their potential applications in the next-generation solid-state lighting sources and flat panel displays, OLEDs have garnered a lot of attention. Several efforts have been devoted to the development of new emissive materials to satisfy market requirements such as high luminescence quantum yield in the solid state, good amorphous film-forming properties, high thermal stability, and color purity.Based on the detailed literature survey, forty-two new conjugated small molecules, viz. C1-42 (Series 1-7) were designed as potential emitters for OLED applications. All of them were successfully synthesized and well characterized. Further, they were subjected to in-depth optical, electrochemical, thermal, theoretical, and electroluminescence studies. The solvatochromic study clearly indicated the nonpolar nature of the ground state and the presence of ICT behavior in the molecules. New OLEDs were fabricated employing selected twenty-eight newly synthesized compounds (Series 1-4) as emitters. From these studies, it is clear that the synthesized molecules possess all the prerequisites to act as an emissive layer in an OLED device. DFT calculations revealed their FMO, HOMO-LUMO energy levels, and spatial charge distribution in the molecules. Interestingly, fabricated devices containing C3, C11, C19 and C26 showed an EQE of 5.32, 5.91, 4.18 and 4.18 %, respectively. In the OLED devices, C3 gives yellow emission, C11 shows green light emission C19 exhibits cyan light and C26 shows bluish-green light.
Molecular design and synthesis of new metal-free organic chromophores for dye sensitized solar cells
(2018) Naik, Praveen; Adhikari, A. Vasudeva
The quest for neat and cost effective renewable energy has led to added research attention on organic photovoltaics. Over the past two decades, the dye-sensitized solar cell (DSSC), which belongs to the thin film photovoltaic technology, has emerged as an attractive and promising lowcost solar device after the inventive research work reported by Gratzel group. Among the different components of DSSCs, the dye as a photosensitizer plays a crucial role in the process of the cells, which include sunlight harvesting and electron injection from excited dye into the CB edge of TiO2. At present, there is a considerable interest among the researchers to design and develop new n- type organic chromophores for DSSC application. In this context, it was planned to design, synthesize and investigate the photovoltaic performance of new organic dyes based on N, N dimethylaniline (Series-1A, n-C1-5) and carbazole (Series-1B to 5, n-C6-21) as n-type sensitizers/co-sensitizers. In addition, it has been contemplated to design and investigate three new carbazole based dyes (Series-6, p-C1-3) as potential p-type sensitizers for DSSC application. Based on the detailed literature survey, twenty one new n-type organic sensitizers/cosensitizers and three p- type organic sensitizers were designed with various design strategies. They were successfully synthesized following appropriate synthetic protocols. Further, they were wellcharacterized by spectral, optical and electrochemical analyses. Their optical and electrochemical parameters along with molecular geometries were optimized, and DFT has been employed to apprehend the effect of structures of organic sensitizers/co-sensitizers on their photovoltaic performances. Finally, the synthesized dyes were subjected to the photovoltaic studies. Among ntype organic sensitizers, the cell fabricated with n-C13 displayed the optimum PCE of 3.55%. Whereas, the co-sensitization studies, indicated that, under the same conditions, the device cosensitized using n-C6 dye with NCSU-10 sensitizer showcased upheld PCE of 9.55%. Finally, the new three p-type organic dyes were sensitized on NiO and their photovoltaic results revealed that, p-C2 sensitized DSSC exhibited optimum photovoltaic performances which are comparable with that of the bench mark reference P1. To sum up, by appropriately optimizing the molecular structures of metal-free organic dyes, it is possible to further ameliorate the photovoltaic performance of the cells.
Synthesis and Characterization of New Donor-Acceptor Type Conjugated Polymers for NLO Applications
(National Institute of Technology Karnataka, Surathkal, 2013) M. S., Sunitha; Adhikari, A. Vasudeva
Over the last two decades, conjugated polymers have received significant, scientific and technological interest due to their broad range of applications. Among various conjugated polymers, donor-acceptor (D-A) type conjugated polymers are in the forefront of research efforts because of their easy processability, stability, and readiness to functionalize. The present research work was concentrated on design, synthesis and characterization of four new series (P1-P16) of D-A type conjugated polymers derived from 3,4-disubstituted thiophene. In the new polymers 3,4-dialkoxy/aryloxy thiophene and 1,3,4-oxadiazole were introduced as electron donor and electron acceptor segments respectively. Also, aromatic systems such as benzene, thiophene, pyridine, phenylenevinylene, EDOT, naphthalene and biphenyl groups were introduced as conjugated spacers in the polymer chain. It was expected that the new polymers would exhibit good electrochemical and optical properties. The new intermediates, monomers and four series of polymers P1-P16 were synthesized through multistep reactions. The structures of new intermediates and monomers were confirmed by FTIR, 1H NMR, 13C NMR spectral methods followed by elemental analyses. Further, the molecular structures of polymers were elucidated by FTIR, 1H NMR spectroscopy, GPC and elemental analysis. Their thermal stability was determined using TGA. The linear optical properties of polymers were investigated by UV-visible absorption and fluorescence spectroscopic studies. The electrochemical properties were determined using cyclic voltammetry (CV). Their bandgap was found to be in the range of 1.8-2.5 eV. Further, their nonlinear optical (NLO) properties were investigated by Z-scan and degenerate four wave mixing (DFWM) methods using 532 nm, 7 ns laser pulses. The effect of different substitution was discussed in detail with regard to electrochemical and optical properties. Polymers of series 1, 2 and 4 showed two-photon absorption (2PA) while polymers of series 3 displayed three-photon absorption (3PA). A further insight on the NLO behavior was provided by employing suitable theories and equations.
Synthesis and characterization of new heterocycle-based discotic mesogens for optoelectronic applications
(National Institute of Technology Karnataka, Surathkal, 2019) D. R, Vinayakumara; Adhikari, A. Vasudeva
Organic π-conjugated molecules are gaining significant attention because of their substantial capability of producing low-cost, eco-friendly, flexible and large-area plastic electronics. Certainly, discotic liquid crystals (DLCs) are renowned soft selfassembled one-dimensional (1-D) organic nanostructures as they possess robust cofacial π-π stacking in the longer columnar axis, which provides a significant channel for effective anisotropic charge mobility. These LC materials are recognized to possess superior potential to be utilized as active semiconducting layers in organic electronic devices in comparison to the organic single crystals or amorphous polymers in terms of several aspects. At present, a significant number of researchers are keenly working on this class of materials for their applications in future optoelectronic devices. In this context, it was planned to design, synthesize optically dynamic unconventional discotic molecules based on various heterocyclic moieties (HT1-35) and to study the structureproperty relationships. Also, it was contemplated to employ the selected LC materials in optoelectronic devices and to evaluate their performance. Based on the thorough literature survey, six series of molecules, i.e. Series-1 to 6 carrying important heterocycles appended with variety of substituted aryl motifs were designed by following different designing strategies. They were successfully synthesized using appropriate synthetic protocols and their chemical structures were confirmed by means of routine spectral techniques. Further, their liquid crystalline properties were investigated by set of standard methods. Most of the newly prepared materials were found to be rich in mesomorphism, dominated with columnar (Col) selfassembly. Furthermore, they were subjected to detailed photophysical as well as electrochemical characterizations and the obtained optoelectronic results were corroborated with theoretical simulations (DFT). Majority of them were shown to be superior light absorption and emitting materials. Finally, the columnar LC materials owning essential properties were employed as emissive layer in the fabrication of multilayer OLED devices; the attained results were promising. Conclusively, by improving the molecular design, prospective DLCs with plausible applications in molecular electronics, can be achieved.
Synthesis, characterization and mesomorphic properties of new pyridine derivatives
(National Institute of Technology Karnataka, Surathkal, 2014) T.N, Ahipa; Adhikari, A. Vasudeva
Luminescent liquid crystals (LC) are fascinating materials and have received significant, scientific and technological interest due to their wide range of applications. Among various LC materials, heterocyclic mesogens gain much interest. This is attributed to the ability of heterocycles to impart lateral and/or longitudinal dipoles combined with their favorable molecular shape. Also, their presence helps for exhibiting good photophysical properties. At present, there is a considerable attention among the researchers to develop new heterocyclic systems showing both liquid crystalline and luminescent properties. In this context, it was contemplated to design, synthesize and to investigate the liquid crystalline as well as optical properties of new pyridine derivatives. Based on the literature survey, new pyridine derivatives (LC1-48) were designed as possible liquid crystalline materials. They were later successfully synthesized following the appropriate synthetic routes. Further, their synthetic methods as well as purification techniques were established and their yields were optimized. Further, their structures were confirmed by various spectral techniques such as FTIR, 1H NMR, 13CNMR spectral, single crystal followed by elemental analyses. Finally, the target compounds were characterized for their mesogenic, optical and optoelectronic properties. The liquid crystalline study on new pyridine derivatives indicated that the compounds LC1, LC14 and LC20-25 were shown to exhibit nematic phase at high temperature and LC2-13, LC15-19, LC26-32 and LC34-48 were shown to display columnar phase at ambient or higher temperature. Similarly, their optical study revealed that the compounds showed a strong absorption band in the range of 330-370 nm in solution state and a strong blue emission band in the range of 390-480 nm both in solution as well as in film state. The optoelectronic study of LC38 evidenced its suitability in device applications. To sum up, suitably substituted new pyridine derivatives appeared as active templates for future development of new liquid crystalline materials.
Synthetic and anticonvulsant studies of some new pyridine derivatives
(National Institute of Technology Karnataka, Surathkal, 2014) Shrikant; Adhikari, A. Vasudeva
Epilepsy is a rapidly growing neurological disorder that affects about 1% of world’s population. The present medications could able to control the seizure generation but none of the developed drugs are able to cure the disease completely. As a result, demand for new and efficient antiepileptic agents is growing day by day. In this connection, it was contemplated to synthesize new active antiepileptic agents. Based on the literature survey, new DHP and imidazo[1,2-a]pyridine derivatives carrying biologically active pharmacophores (P1-138) were designed as possible anticonvulsant agents. The newly designed compounds were later successfully synthesized following the appropriate synthetic routes. Further, their synthetic methods as well as purification techniques were established and their yields were optimized. They were later characterized by various spectral techniques such as FTIR, 1H NMR, 13C NMR, mass spectral followed by elemental analyses. Finally, the target compounds were screened for their antiepileptic studies following Maximal Electroshock Seizure (MES) and subcutaneous Pentylene Tetrazole (scPTZ) methods. Further, the neurotoxicity study of target compounds was performed by Rotarod technique, in order to establish their toxicity profile. At the end, based on the in vivo results, their Structure-Activity Relationship (SAR) was discussed. The in vivo results of preliminary anticonvulsant screening study indicated that newly synthesized DHPs carrying hydrazone and amide functionalities (P1-40) are moderately active antiepileptic agents in MES method. On the other hand, significant activity was observed for new imidazo[1,2-a]pyridines (P41-138) carrying various pharmacophores at position-2 and position-3. Particularly, those imidazo[1,2- a]pyridines carrying oxazolone, cyanopyridone, 1,2,3-triazole, 1,2,4-triazole and hydrazone groups exhibited pronounced activity. Interestingly, the Rotarod study revealed that most of the tested compounds are non-toxic, which further appreciated the choice of new derivatives as antiepileptic agents. Altogether, the suitably substituted new imidazo[1,2-a]pyridines carrying electron donor groups appeared as active templates for future development of new antiepileptic agents.