Faculty Publications
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Item Possible Room-Temperature Ferromagnetism in Self-Assembled Ensembles of Paramagnetic and Diamagnetic Molecular Semiconductors(American Chemical Society service@acs.org, 2016) Dhara, B.; Tarafder, K.; Jha, P.K.; Panja, S.N.; Nair, S.; Oppeneer, P.M.; Ballav, N.Owing to long spin-relaxation time and chemically customizable physical properties, molecule-based semiconductor materials like metal-phthalocyanines offer promising alternatives to conventional dilute magnetic semiconductors/oxides (DMSs/DMOs) to achieve room-temperature (RT) ferromagnetism. However, air-stable molecule-based materials exhibiting both semiconductivity and magnetic-order at RT have so far remained elusive. We present here the concept of supramolecular arrangement to accomplish possibly RT ferromagnetism. Specifically, we observe a clear hysteresis-loop (Hc ? 120 Oe) at 300 K in the magnetization versus field (M-H) plot of the self-assembled ensembles of diamagnetic Zn-phthalocyanine having peripheral F atoms (ZnFPc; S = 0) and paramagnetic Fe-phthalocyanine having peripehral H atoms (FePc; S = 1). Tauc plot of the self-assembled FePc···ZnFPc ensembles showed an optical band gap of ?1.05 eV and temperature-dependent current-voltage (I-V) studies suggest semiconducting characteristics in the material. Using DFT+U quantum-chemical calculations, we reveal the origin of such unusual ferromagnetic exchange-interaction in the supramolecular FePc···ZnFPc system. © 2016 American Chemical Society.Item Blue emitting 1,8-naphthalimides with electron transport properties for organic light emitting diode applications(Elsevier B.V., 2017) Ulla, H.; Raveendra Kiran, M.R.; Garudachari, B.; Ahipa, T.N.; Tarafder, K.; Vasudeva Adhikari, A.; Umesh, G.; Satyanarayan, M.N.In this article, the synthesis, characterization and use of two novel naphthalimides as electron-transporting emitter materials for organic light emitting diode (OLED) applications are reported. The molecules were obtained by substituting electron donating chloro-phenoxy group at the C-4 position. A detailed optical, thermal, electrochemical and related properties were systematically studied. Furthermore, theoretical calculations (DFT) were performed to get a better understanding of the electronic structures. The synthesized molecules were used as electron transporters and emitters in OLEDs with three different device configurations. The devices with the molecules showed blue emission with efficiencies of 1.89 cdA-1, 0.98 lmW?1, 0.71% at 100 cdm-2. The phosphorescent devices with naphthalimides as electron transport materials displayed better performance in comparison to the device without any electron transporting material and were analogous with the device using standard electron transporting material, Alq3. The results demonstrate that the naphthalimides could play a significant part in the progress of OLEDs. © 2017 Elsevier B.V.Item Salt/Cocrystal of Anti-Fibrinolytic Hemostatic Drug Tranexamic acid: Structural, DFT, and Stability Study of Salt/Cocrystal with GRAS Molecules(American Chemical Society service@acs.org, 2019) Nechipadappu, S.K.; Reddy, I.R.; Tarafder, K.; Trivedi, D.R.Tranexamic acid (TXA) is an important and essential medicine needed in a health system and is approved by the US FDA for the treatment of excessive blood loss from trauma, postpartum bleeding, surgery, tooth removal, nosebleeds, and heavy menstruation. One of the notable disadvantages of the TXA drug is that has low absorption (â35-40%) in the gastrointestinal tract, possibly due to its amphoteric nature. In the present work, nine molecular salts and two cocrystals of the TXA molecule have been synthesized by a simple water-mediated solvent evaporation method. The coformers/counterions used were salicylic acid (SAL), 3-hydroxybenzoic acid (3HBA), 2,4-dihydroxybenzoic acid (2,4HBA), 2,5-dihydroxybenzoic acid (2,5HBA), 2,6-dihydroxybenzoic acid (2,6HBA), gallic acid (GAA), oxalic acid (TXA), tartaric acid (TTA), fumaric acid (FUM), succinic acid (SUA), and crotonic acid (CRA). The synthesized salts/cocrystals were characterized by various spectroscopic, thermal, and XRD techniques. The crystal structures of all of the molecular adducts were determined by SC-XRD techniques. In the synthesized salts, charge-assisted acid···amine heterosynthons and O-H···O hydrogen bonds between the acid group of TXA and the coformer are favored, and the salts TXA-FUM and TXA-SUA were found to be isostructural on the basis of the isostructural parameters Ï€ and Î? . In the cocrystal, molecules interacted through the acid group of the coformer with the carboxyl group of the TXA molecule. Further, these salts/cocrystals were found to be stable for a period of 6 months under ambient conditions (â25-30 °C, â60-65% RH). Furthermore, density functional theory (DFT) calculations were carried out to better understand the geometric structure of the molecules presented in our study. The interaction energies of the molecular salts and cocrystals were calculated, and they supported the reported structure of the crystalline adducts. The cocrystal formation in the case of TXA-GAA and TXA-CRA has been confirmed by a DFT calculation study, as the salt formation in these cases resulted in a higher interaction energy in comparison to the cocrystal. Consequently, these molecular salts offer promise for the development of new drug products of TXA, and a few salts, namely TXA-SAL and TXA-2,5HBA, offer the possibility of development of combination drugs. © 2018 American Chemical Society.Item Enhanced quantum capacitance in chemically modified graphene electrodes: Insights from first principles electronic structures calculations(Elsevier B.V., 2021) Sruthi, T.; Tarafder, K.We have carried out a systematic study of quantum capacitance in functionalized graphenes by using DFT calculations. The graphene functionalization has been done by doping with different aliphatic and aromatic molecules and their radicals. The quantum capacitance of functionalized graphenes was estimated from the accurate electronic band structures of the system obtained by using DFT calculations. Our theoretical investigation reveals that aromatic and aliphatic radicals introduce localized density of states near the Fermi level of the functionalized systems, due to a charge localization. As a result, a very high quantum capacitance (>230?F?cm2) was observed in the system. The effects of atomic dislocation and the vacancy defect on graphene during functionalization has also been incorporated in our investigation. Our study suggests an effective way to synthesize highly efficient graphene-based supercapacitor electrode materials by using aromatic and aliphatic molecule/ radical functionalization of graphene. © 2020 Elsevier B.V.Item Understanding and tuning of spinterface for chemisorbed Ni-dinuclear quinonoid on Co(001) substrate(IOP Publishing Ltd, 2021) Reddy, I.R.; Tarafder, K.Planar magnetic molecules are of great research interest in the past few years because of their possible application in molecular spintronics. Microscopic understanding of the adsorption and magnetic exchange interaction of these molecules to the metallic/magnetic surfaces may pave the way in developing efficient molecular spin switching devices. Herein, using density functional theory + U calculations, we have studied the structural, electronic, and magnetic properties of a Ni-dinuclear molecule chemically adsorbed on a Co(001) substrate. Switching of the spin and oxidation state of the Ni atom present in the molecule was observed due to the adsorption. We report a strong antiferromagnetic coupling between the spins of the Ni-dinuclear molecule to the ferromagnetic Co(001) substrate. The study reveals an indirect exchange interaction between the magnetic center of the molecule and the substrate Co atoms. The exchange interaction is mediated through the ligands of the molecule that stabilizes the spin moment of the molecule in an antiferromagnetic alignment to the substrate magnetization. Our study also shows that the spin state and strength of MAE of the adsorbed molecule can be tailored through the magneto-chemical method by adding the Cl atom as an axial ligand to the magnetic center of the molecule. © 2021 IOP Publishing Ltd.Item Revealing the Microscopic Picture of the Charge Transfer Mechanism between Graphene and Dopant Molecules(American Chemical Society, 2023) Khandelwal, V.; Srivastava, P.K.; Nagaraja, S.; Yadav, P.; Tarafder, K.; Ghosh, S.It is generally recognized that the dipole moment of the adsorbed molecules is a crucial factor in determining the charge-transfer interaction between molecules and graphene. However, the microscopic details of this process have remained elusive. In this study, we experimentally investigate the charge-transfer interaction between adsorbed molecules and graphene, which holds great promise for achieving controllable doping. By trapping various molecules at the graphene-substrate interface, our results emphasize that the doping effect primarily depends on the reactivity of the constituent atoms in the attached molecules rather than just their dipole moment. Observation of (i) the emergence of the Raman D peak exclusively at the edges for trapped molecules without reactive atoms, and throughout the entire basal plane for those with reactive atoms, and (ii) variations in the density of attached molecules (with and without reactive atoms) to graphene with their respective dipole moments provides compelling evidence to support our claim. These findings are well-supported by experimental results and first-principles density functional theory calculations. © 2023 American Chemical Society.Item Graphene Straintronics by Molecular Trapping(American Chemical Society, 2025) Srivastava, P.K.; Khandelwal, V.; Reddy, I.R.; Tarafder, K.; Ghosh, S.Here, we report on controlling strain in graphene by trapping molecules at the graphene–substrate interface and leveraging molecular dipole moments. Spectroscopic and transport measurements reveal that strain correlates with the dipole moments of trapped molecules extending beyond their molecular sizes, where values ranging from 1.5 to 4.9D lead to a 50-fold increase in strain and a significant rise in residual carrier density. This has been possible by charge transfer between graphene and trapped molecules, altering the C?C bond length and causing biaxial strain. First-principles density functional theory calculations confirm a consistent dependence of the bending height on molecular dipole moments. © 2025 American Chemical Society