Department of Chemistry

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Author: search.filters.author.Sarkar, Madhushree

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    Selective sensing of picric acid using a Zn(II)-metallacycle: experimental and theoretical validation of the sensing mechanism and quantitative analysis of sensitivity in contact mode detection
    (RSC, 2024) Sarkar, Madhushree
    A combination of N,N′,N′′-tris(3-pyridyl)-1,3,5-benzenetricarboxamide (L1) and p-chlorobenzoic acid (HL2) with Zn(NO3)2·6H2O resulted in the formation of a dinuclear metallacycle [ZnL1(L2)2(DMF)2]2 (1(DMF)4). In 1(DMF)4, the Zn(II) centre adopts a square pyramidal geometry, while one of the pyridyl N out of the three pyridyl groups in L1 remained uncoordinated. Solvated DMF molecules are present in 1(DMF)4. The structural and chemical nature of 1(DMF)4 is effective for it to act as a potential fluorescent probe for the detection of nitroaromatic compounds. It is observed that the probe, 1(DMF)4, could selectively detect picric acid (PA) among various aromatic compounds in solution (DMSO), while the solid state (contact mode) detection showed a positive sensing response for the nitrophenols (PA: 87% quenching efficiency, 2,4-dinitrophenol (2,4-DNP): 57% quenching efficiency and 4-nitrophenol (4-NP): 40% quenching efficiency). The limit of detection (LOD) of PA by the probe in DMSO was found to be 6.8 × 10−11 M while the LOD in contact mode detection was estimated to be 0.49 ng cm−2. The mechanism of selective detection of PA by 1(DMF)4 in DMSO was analyzed through photophysical studies, 1H-NMR experiments and also by density functional theory (DFT) calculations. The effective overlap of the absorption spectrum of 1(DMF)4 and emission spectrum of PA in DMSO suggests that the Förster resonance energy transfer (FRET) is responsible for quenching phenomena in DMSO. The DFT calculations and molecular docking studies showed the adduct formation due to the favorable interactions between 1(DMF)4 and PA in DMSO, while negligible interactions were observed between 1(DMF)4 with other aromatic compounds. The experimental and DFT studies showed that the efficient sensing ability of PA by 1(DMF)4 in the solid-state was due to photoelectron transfer (PET) and FRET phenomena described herein.
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    Mechanistic insights on chemosensing response of pyrene and anthracene based fluorescent probes towards nitroaromatic compounds
    (Wiley, 2024-12) Sarkar, Madhushree
    Two polyaromatic hydrocarbon-based compounds, N2,N4,N6-tris-((pyren-1-yl)methyl)-1,3,5-triazine-2,4,6-triamine (SM1) and N2,N4,N6-tris-((anthracen-9-yl)methyl)-1,3,5-triazine-2,4,6-triamine (SM2) are explored as chemosensors for detecting nitroaromatic compounds. The chemosensing studies of SM1 and SM2 showed selective sensing of 4-nitroaniline (4NA) in homogeneous medium (in Acetonitrile (ACN) and in DMSO), which is due to the hyperpolarizability of 4NA. Quenching mechanism studied for the three analytes (4NA, 2NA and PA) showed dynamic quenching in SM1 in presence of 4NA and 2NA, while static quenching in presence of PA. Solvent effect on the chemosensing response of SM1 and SM2 towards PA was observed and it showed enhancement in the response on changing the solvent from ACN to DMSO to water. DFT studies, photophysical analysis, NMR experiments and complex synthesis experiments were done to provide in depth analysis on the observed sensing phenomena. Both SM1 and SM2 being insoluble in water, were used as heterogeneous chemosensors in aqueous medium, where selective sensing was observed for 4NA and PA. The LOD of PA and 4NA by SM1 in water was found to be 1.3 ppt and 2.1 ppt, respectively. The recyclability and stability after sensing studies were confirmed by PXRD.
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    A facile and efficient synthesis of bodipy-based fluorescent probes for selective detection of hydrazine
    (Wiley, 2024-11) Sarkar, Madhushree; Kumar, Dalip
    A facile and ratiometric BODIPY-based fluorescent probe 4 was developed for the selective detection of hydrazine in solution phase. The BODIPY-based fluorophores 3 and 4 were easily prepared in high yields from the L-proline catalyzed reaction between α/β-formyl BODIPY 1 a/1 b and 3-cyanoacetylindole 2. Use of easily accessible substrates, benign solvent, catalytic amount of L-proline and high product yields are the advantageous features of the developed protocol. Prepared BODIPYs 3 (536 nm) and 4 (567 nm) showed bathochromic shifts (36–67 nm) in UV-Visible absorption maxima when compared to parent BODIPY (500 nm) in dichloromethane (DCM). The stable and economical BODIPY-based probe 4 exhibited rapid response and remarkable selectivity towards hydrazine when compared to other commonly occurring analytes. At low concentration, the BODIPY probe 4 (10 μΜ) is non-fluorescent, however, a significant enhancement in fluorescent (turn-on) was observed with the increasing concentration of hydrazine (0–100 μΜ). This change in fluorescent behaviour may be ascribed to intramolecular charge transfer (ICT) effect as supported by density functional theory (DFT) calculations. With a 4.3 μM detection limit, the BODIPY probe 4 was also found to be useful in detecting hydrazine in real environmental samples.
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    Bis-Pyridyl Diimines as Selective and Ratiometric Chemosensor for Ni(II) and Cd(II) Metal Ions
    (Wiley, 2019-01) Sarkar, Madhushree
    A pyridyl based Schiff base compound, (1E,1′E)-N,N′-(butane-1,4-diyl)bis(1-(pyridin-2-yl)methanimine) (2pdab) was observed to serve as a highly selective and sensitive ratiometric chemosensor for Ni2+ and Cd2+ ions. Mole ratio method and Yoe Jone's method showed a 1:1 binding mode of metal ions (Ni2+ and Cd2+) with 2pdab, while a binding constant of 26.88 ×106 L/mol and 4.29×106 L/mol, for Ni2+ and Cd2+, respectively, was determined. The limit of detection of 2pdab in sensing Ni2+ and Cd2+ was observed to be 3.08 μM and 1.4688 μM, respectively. The selectivity of 2pdab to detect Cd2+ and Ni2+ among various other competitive ions was also studied. The sensor, 2pdab, was applied in real time application for detection of nickel ion in river water sample
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    Template effect of innocent and coordinating anions on the formation of interpenetrated 2D and 3D networks: methyl orange and iodine sorption studies
    (RSC, 2020) Sarkar, Madhushree
    A 2D Cd(II) coordination polymer [Cd2(L1)4(H2O)4][ClO4]4·5(H2O), CP1, was synthesized with 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (L1) while the use of benzene-1,3-disulphonate (L2) along with L1 resulted in a novel 3D Cd(II) coordination polymer, [Cd(L1)2(L2)]·2(H2O)·(CH3OH), CP2. CP1 attained a threefold interpenetrated 2D staircase network where the channels are filled with H2O and ClO4− anions. CP2 has a 3D interpenetrated structure and has small pores. The chemical nature and size of the pores of CP1 and CP2 are effective in adsorbing organic dye molecules. Selective adsorption of upto 96% of methyl orange (MO) within 10 min was observed in CP1 and CP2. CP2 was also studied for the adsorption and desorption of iodine. CP1 and CP2 showed luminescence and their solid state PL has a strong emission peak at ∼484 nm. The structural analysis of L1 and [HL1][ClO4] showed the effect of ClO4− on the supramolecular assembly and geometry of the molecules of L1.
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    Increased Photocatalytic Activity of Post Synthetically Modified Coordination Polymer Derived from Bis-pyridyldiamide
    (Wiley, 2020-07) Sarkar, Madhushree
    A one-dimensional looped chain coordination polymer (CP1) is synthesized by the reaction of CoII with N1,N3-di(pyridine-4-yl)isophthalamide. Transmetalation reaction of CP1 with CuII showed single-crystal-to-single-crystal (SC-SC) transformation to form CP2, which is also a 1D looped chain. Both CP1 and CP2 showed the presence of DMF as guest molecules near the loops of the 1D chains. CP1 and CP2 were found to have bandgap of 2.41 eV and 1.30 eV, respectively, which were calculated by Tauc plot. The difference observed in the optical bandgap of CP1 and CP2 is reflected in photocatalytic dye degradation studies. It was observed that CP2 showed much greater efficiency in degrading the dyes (Methylene blue, Methyl orange and Rhodamine B) as compared to that of CP1. The polar nature of the loops of the chains in CP1 and CP2 due to the presence of DMF was exploited to study the adsorption and desorption of I2. Adsorption of I2 in CP1 and CP2 was found to follow first order kinetics with a rate constant of 8.32  ×  10–5 s–1 for CP1 and 9.71  ×  10–5 s–1 for CP2. Guest inclusion reaction was performed to incorporate benzotriazole in the CP1. Impedance measurements showed a higher conductivity in the benzotriazole incorporated CP1.
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    Controlling light emitting properties in bis(pyrenyl)-di-imines by tuning the chemical functionality of the spacer group
    (RSC, 2021) Sarkar, Madhushree
    Aggregation-caused quenching (ACQ) and aggregation-induced emission (AIE) are dictated by the molecular aggregation which in turn is decided by the chemical features present in a molecule. The photophysical properties of bis(pyrenyl)-di-imines were investigated in solution as well as the solid state. It was observed that the light-emitting properties are dependent on the type of spacer group present in the compound. The presence of an alkylene spacer [ethylene (L3), butylene (L4), and hexylene (L5)] in bis(pyrenyl)-di-imines showed AIE at higher concentrations as well as in the solid state whereas the presence of a phenylene (L1) spacer and the absence of any alkyl/aryl spacer (L2) in the compound have resulted in ACQ in the solid state. Crystal structure analysis of L1 has explained its non-emissive nature in the solid state, while the AIE in the compounds, L3–L5, where flexible alkylene spacers are present, provided an idea about the solid-state arrangement of the molecules.
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    Structural analysis of bis(pyridyl)diimines: Factors affecting the molecular geometry and supramolecular packing
    (Elsevier, 2022-02) Sarkar, Madhushree
    Systematic analysis of structural features of a series of bis(pyridyl)diimines is done to have an understanding on the effect of different types of interactions in modulating the molecular geometry and final packing of the molecules in the solid state. Supramolecular synthons that may result from weak interactions such as Csingle bondH···N and aromatic interactions are difficult to predict and hence analyzing homologous series of compounds, which can organize only by weak interactions will lead to generating data sets on various possibilities of synthons. In the series of bis(pyridyl)diimines, small variation in the molecular features such as position of nitrogen on pyridyl ring, presence of hydrogen or methyl group on imine carbon and changing the alkyl spacer length is being related to the observed changes in the occurrence of non-covalent interactions and finally in the crystal packing in the solid state. Cooperative effect of intermolecular interactions and steric factors decide the final structural arrangement, which is being inferred by observing the solid state arrangement of the compounds. Crystallization induced emission of the bis(pyridyl)diimines is also studied and correlated with their structural features and the overall supramolecular architecture.
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    Positional effects of a pyridyl group in Zn(II) coordination polymers on the selective dye adsorption properties
    (Elsevier, 2022-03) Sarkar, Madhushree
    Three 1D zig-zag chain coordination polymers {[Zn(L1)](I)2}n (CP1), {[Zn(L2)](I)2}n (CP2) and {[Zn(L3)](I)2}n (CP3) were synthesized under the self-assembly conditions, where L1 = 1,2-bis(pyridin-3-ylmethylene)hydrazine; L2 = 1,2-bis(1-(pyridin-3-yl)ethylidene)hydrazine; L3 = 1,2-bis(1-(pyridin-4-yl)ethylidene)hydrazine. The molecular structures of CP1, CP2 and CP3, were determined by single crystal X-ray diffraction studies. Ligands L1 and L2 differ from L3 in terms of position of nitrogen atom on the pyridyl group, while L1 and L2 differs from each other with respect to the presence of hydrogen or methyl group on the imine carbon. These minor structural differences in the ligands has affected the electronic environment and the chemical nature of the chains formed in these Zn(II) coordination polymers. Hirshfeld surface (HS) analysis has been performed on CP1, CP2 and CP3 in order to determine the intermolecular interactions present in the crystal lattice and it is in well agreement with the single crystal XRD analysis of the hydrogen bonding interactions. Selective dye adsorption behavior was observed for CP3, which showed considerable adsorption of Methyl Orange (MO) and sodium salt of Methyl Red (MR) whereas CP1 and CP2 do not show any adsorption properties at all. Further it was observed that adsorption by CP3 was selective only for an anionic dye - Methyl Orange (MO) and sodium salt of Methyl Red (MR) whereas cationic dyes such as Methylene Blue (MB), Malachite Green (MG), Rhodamine-B (RB) were not adsorbed by CP3. These studies showed the importance of chemical nature of the ligands in coordination polymers on the adsorption properties. Although being 1D chain without any pores, CP3 was capable of holding the dyes in between the neighboring chains due to the electronic effects resulted from the coordination of the ligand L3 with the Zn(II) center.
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    Bis(2-pyridyl)diimine as a naked eye colorimetric fluorescence turn off probe selectively for Fe(II) ions as a consequence of energy changes in the electronic states upon complexation
    (Elsevier, 2022-08) Sarkar, Madhushree
    Bis(pyridyl)diimine, (1E,1′E)-N,N'-(ethane-1,2-diyl)bis(1-(pyridin-2-yl)methanimine) (L) has coordinating nitrogen atoms in effective positions to form stable chelates with metal ions and is capable of capturing a range of transition metal ions. However, the selective colorimetric response of Fe(II) by using L was observed. Colourless to purple coloured transition resulted on complexation of L with Fe(II) ions selectively and was not affected by the presence of other transition metal ions including Fe(III) ions. Photoluminescence studies have shown the quenching of emission maxima corresponding to L in the presence of Fe(II) ions along with appearance of new peaks at higher wavelength regions. Appearance of a specific color change, which can be visualized by naked eye and an added photophysical feature involving quenching of emission spectra, particularly for Fe(II) are associated with the changes in the electronic state energies of L upon complexation with Fe(II). Thermodynamic estimation of complex stability was done by determining the binding constant of the complex, which was found to be 7.2 × 1010 M−2 using Yoe Jones method. A binding ratio of 1:2 for L and Fe2+ was determined experimentally with help of mole ratio method, which hinted at the geometrical possibilities of the complex of L with Fe(II).). Limit of detection (LOD) for the identification of Fe(II) ions with L was determined using colorimetric naked eye method and was found to be 25 μM. Further L was also used to detect Fe(II) in real sample i.e. river water. NMR analysis supported the low spin state of Fe(II) in the Fe(II)-L complex. Anticipated geometry of the Fe(II)-L complex was optimized using Gaussian09 software through the B3LYP method, which upon investigation of the energies of frontier molecular orbitals, provided the details related to the electronic properties associated with the complexation of Fe(II) and L.