K. Bhanuprakash

Indian Institute of Chemical Technology, Bhaganagar, Telangana, India

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Publications (106)278.96 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Two novel heteroleptic Ru[3+2+1] sensitizers, 1 and 2, with unsymmetrical bipyridine as ancillary ligand and electron donating 4-methylstyryl group in the anchoring π-extended terpyridyl ligand were synthesized and characterized. DFT studies reveal that the lowest unoccupied molecular orbital (LUMO) is distributed over the terpyridine. The two new sensitizers showed an improvement in the molar extinction coefficient compared to reference standard N749 dye. Among the two new sensitizers, 1 exhibited maximum solar to electric conversion efficiency (η) of 5.19% with short circuit current density of 14.032 mA cm−2, open circuit voltage of 0.520 V and fill factor of 0.712, under Air Mass (AM) 1.5 sunlight, while the reference N749 sensitized solar cell exhibited η-value of 6.44%.
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    ABSTRACT: We report here a simple one-pot synthesis, characterization and cation recognition properties of two benzothiazole based ferrocenyl pyrazoline derivatives (4 and 5). These compounds behave as highly selective multichannel sensors towards Hg2+ and Cu2+ ions in acetonitrile solution. An anodic shift of the ferrocene/ferrocenium couple, with a progressive perturbation in the lower energy band, was observed upon interaction of the cations with these receptors. A colour change, from yellow to brown and red, for Hg2+ and Cu2+ ions respectively enabled facile “naked eye” detection using the ‘test strips’ prepared from these receptors. The competitive metal-ion binding experiments indicated high selectivity towards Hg2+ as compared to Cu2+ ions. A 45–59 fold chelation enhancement of fluorescence (CHEF) towards Hg2+ ion was observed in the emission spectrum of 4 and 5. 1H NMR studies and DFT calculations were used to determine the binding sites of receptor 4 involved in the complexation process.
    Journal of Organometallic Chemistry 03/2015; 780. DOI:10.1016/j.jorganchem.2014.12.027 · 2.30 Impact Factor
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    ABSTRACT: Keeping in view to suggest one more class of molecules in order to make a choice and assessment of exchange-correlation (XC) functionals, symmetrical squarylium dye (SQ) derivatives have been considered and Le Bahers's diagnostic indexes have been applied to study the electronic transition character of these molecular systems through TD-DFT and SAC-CI methods. Unlike calculated absorption using SAC-CI, the TD-DFT results are not matching with experimental absorption data. However, the diagnostic indexes obtained with TD-DFT and SAC-CI are apparently similar for all methods. This indicates that care should be taken while choosing XC functionals and assessing the nature of electronic transitions of a specific class of molecules. The centroids of charges associated with the density increase and depletion regions are localized on central C4 ring and carbonyl groups and with a small extension up to side aromatic substitution of the SQ dye derivative. Hence the electronic transition occurring in this class of molecules is confined mainly within the central part of molecule. This is in contrast to Donor-Acceptor-Donor type structure in which charge depletion region is expected at side aromatic substitution of the molecule. The small values of calculated transferred charge (qCT) upon excitation lend support to the theory that the electronic transition in this class of molecules is not CT excitation. This is in agreement with our earlier finding that biradicaloid character and orbital interactions are playing key role in their NIR absorption. Hence highly correlated, single reference and multi-determinant SAC-CI method is able to explain the nature of electronic excitations in these molecules rather than TD-DFT with various type of XC functionals.
    RSC Advances 01/2015; 5(24):18813-18821. DOI:10.1039/C4RA10649K · 3.71 Impact Factor
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    ABSTRACT: Two new Ru(II) complexes bearing with substituted dipyrrinato ligands (GS3 and GS10) have been successfully synthesized and characterized. These sensitizers exhibit panchromatic light harvesting properties, rendering them promising for DSSC applications. GS3 has shown high overall power conversion efficiency (η = 2.79%) compared to GS10 which is the highest so far in the case of Ru (II) dipyrrinato dyes. Density functional theory (DFT) and time-dependent DFT calculations were measured for GS3 and GS10 to understand their structural, electronic and photophysical properties.
    Electrochimica Acta 01/2015; 153:343-351. DOI:10.1016/j.electacta.2014.11.198 · 4.50 Impact Factor
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    ABSTRACT: We designed and synthesized a new ruthenium complex using terpyridine as an anchoring ligand and BOC (tertbutyloxycarbonyl) protected bidentate benzimidazole derivative as an ancillary ligand, coded as GS7. The complex was characterized using H-1 NMR, FTIR, elemental analysis, UV-vis spectrophotometer, and cyclic voltammetry. We also tested photovoltaic performance of this complex for dye-sensitized solar cell (DSSCs). GS7 when used as a sensitizer for DSSCs with iodine triiodide electrolyte, showed a J(sc) of 15.25 mA cm(-2), a V-oc of 0.576 V, a FF of 0.691 and overall power conversion efficiency of (eta) 6.07%. (C) 2014 Published by Elsevier B.V.
    Inorganic Chemistry Communications 01/2015; 51. DOI:10.1016/j.inoche.2014.10.033 · 2.06 Impact Factor
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    ABSTRACT: Palmierite Ba3V2O8 and related Cu- and N-doped congeners were prepared by sol-gel, ion-exchange, and solid-state reactions, respectively, with the aim of tailoring their optical, electronic, and photocatalytic properties. The catalysts were characterized by XRD analyis, UV/Vis diffuse reflectance spectroscopy, SEM with energy-dispersive X-ray spectroscopy, photoluminence spectroscopy, BET measurements, thermogravimetric analysis, X-ray photoelectron spectroscopy, and TEM analysis. The electronic structures of Cu- and N-doped optimal compositions were calculated theoretically on the basis of density functional theory. A series of photocatalytic degradation experiments of methylene blue under visible light irradiation disclosed the optimal dopant concentrations of Cu and N into Ba3V2O8, and the photocatalytic ability of the optimal compositions was also tested by the degradation of aniline. The differences in the degradation performance of Cu- and N-doped samples are discussed on the basis of inextricably linked parameters such as photoabsorption, electronic structure, and mobility of the photoinduced charge carriers.
    Berichte der deutschen chemischen Gesellschaft 11/2014; 2014(32). DOI:10.1002/ejic.201402577
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    ABSTRACT: Molecular first hyperpolarizabilities (nonlinear optical responses) of selected s-triazine based heteroaromatic molecules are determined using experimental methods. A large enhancement in nonlinear optical response, in spite of a relatively weak donor–acceptor system, is observed. We have carried out a detailed analysis using computational chemistry techniques to account for this behavior.
    Journal of Molecular Structure 10/2014; 1075:118–123. DOI:10.1016/j.molstruc.2014.05.061 · 1.60 Impact Factor
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    ABSTRACT: Four new organic dyes, coded as CSORG6, CSORG7, CSORG8 and CSORG9, comprising electron rich thiophene derivatives as antennas and cyanoacrylic acid as acceptor, bridged by phenothiazine or phenoxazine were designed and synthesized for dye-sensitized solar cells applications. They were fully characterized with their photophysical, electrochemical properties, density functional theory (DFT), time dependent density DFT (TDDFT) and the light-harvesting properties of the new sensitizers were evaluated with nanocrystalline TiO2-based devices. Among the four diheteroanthracene based dyes, phenoxazine (CSORG7 and CSORG9) based devices afforded the best photovoltaic performance (eta) of 6% under standard AM 1.5G solar irradiation, whereas, N719 showed (eta) 6.4% under the similar fabrication and evolution conditions.
    Synthetic Metals 09/2014; 195:208–216. DOI:10.1016/j.synthmet.2014.06.009 · 2.22 Impact Factor
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    ABSTRACT: In an attempt to develop small organic molecules with potential applications as donors in organic photovoltaic (OPV) devices, we have synthesized and characterized four novel benzothiadiazole (A) core structured D-π-A-π-D dyes featuring carbazole and benzocarbazole as donors (D) and fluorene and thiophene as spacers (π). The effects of the π-spacer units and variations in donor strength on the photophysical, electrochemical and thermal properties of the molecules have been investigated in detail. The replacement of fluorene by thiophene as a π-spacer promotes planarity, resulting in a larger bathochromic absorption shift, enhanced emission profiles and an enhanced intramolecular charge transfer (ICT) transition. The introduction of the benzocarbazole unit creates a low-lying HOMO level, as inferred from cyclic voltammetry studies. All the dyes exhibit remarkable thermal robustness. Theoretical calculations have been carried out to understand the structure–property relationships of the synthesized materials. The results obtained from the characterization methods reveal that the dyes with thiophene π-spacers show better optoelectronic properties compared to their fluorene counterparts. Solution-processable bulk-heterojunction devices with a structure of ITO/PEDOT:PSS (38 nm)/active layer/Ca (20 nm)/Al (100 nm) were fabricated using the materials investigated in this study as donors and (6,6)-phenyl C61-butyric acid methyl ester (PC61BM) as an acceptor. A power conversion efficiency of 1.62% for the molecule with thiophene as a spacer and carbazole as donor/PC61BM was achieved for the preliminary photovoltaic devices under simulated AM 1.5 illumination (100 mW cm−2).
    RSC Advances 08/2014; 4(67). DOI:10.1039/C4RA02700K · 3.71 Impact Factor
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    ABSTRACT: We report the improvement of the light-harvesting property in the bulk heterojunction organic polymer solar cell based on poly(3-hexylthiophene) (P3HT) and PC70BM, with the incorporation of a nearinfrared absorbing squaraine (SQ) dye, bis[4-(2,6-di-tert-butyl)vinylpyrylium] squaraine (TBU-SQ). With the incorporation of TBU-SQ dye (2.5% by wt) in a P3HT:PC70BM (1:1 wt ratio) blend, the power conversion efficiency (PCE) has been enhanced up to 4.55% as compared to 3.47% for the device based on the P3HT:PC70BM binary blend. The improvement in the photovoltaic performance with the incorporation of TBU-SQ attributed to the improvement in the light-harvesting efficiency in the near-infrared region of solar spectrum and increased exciton dissociation into free charge carriers in the ternary blended film. The PCE has been further enhanced to 5.15% when the thermally annealed P3HT:TBUSQ:PC70BM blend was used as the photoactive layer. It was observed that the absorption profile of the active layer was broadened upon thermal treatment as a result of the red shift as well as widening of the P3HT absorption band and the slight red shift of the TBU-SQ absorption peak in the blended film. The improved light-harvesting property of the thermally annealed film and balanced charge transport in the device were attributed to the improvement in the PCE. These results show that TBU-SQ is a promising molecular sensitizer for increasing the PCE of P3HT:PC70BM-based polymer solar cells.
    ACS Sustainable Chemistry & Engineering 07/2014; 2(7):1743-1751. DOI:10.1021/sc500276u
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    ABSTRACT: A tertiary arylamine compound (DC), which contains a terminal cyano-acetic group in one of its aryl groups, and an unsymmetrical porphyrin dyad of the type Zn[Porph]-L-H-2[Porph] (ZnP-H2P), where Zn[Porph] and H-2[Porph] are metallated and free-base porphyrin units, respectively, and L is a bridging triazine group functionalized with a glycinemoiety, and were synthesized and used for the fabrication of co-sensitized dye-sensitized solar cells (DSSCs). The photophysical and electronic properties of the two compounds revealed spectral absorption features and frontier orbital energy levels that are appropriate for use in DSSCs. Following a stepwise co-sensitization procedure, by immersing the TiO2 electrode in separate solutions of the dyes in different sequence, two co-sensitized solar cells were obtained: devices C (ZnP-H2P/DC) and D (DC/ZnP-H2P). The two solar cells were found to exhibit power conversion efficiencies (PCEs) of 6.16% and 4.80%, respectively. The higher PCE value of device C, which is also higher than that of the individually sensitized devices based on the ZnP-H2P and DC dyes, is attributed to enhanced photovoltaic parameters, i.e. short circuit current (J(sc) = 11.72 mA/cm(2)), open circuit voltage (V-oc = 0.72 V), fill factor (FF = 0.73), as it is revealed by photovoltaic measurements (J-V curves) and by incident photon to current conversion efficiency (IPCE) spectra of the devices, and to a higher total dye loading. The overall performance of device C was further improved up to 7.68% (with J(sc) = 13.45 mA/cm(2), V-oc = 0.76V, and FF = 0.75), when a formic acid treated TiO2 ZnP-H2P co-sensitized photoanode was employed (device E). The increased PCE value of device E has been attributed to an enhanced J(sc) value (= 13.45 mA/cm(2)), which resulted from an increased dye loading, and an enhanced V-oc value (= 0.76 V), attributed to an upward shift and increased of electron density in the TiO2 CB. Furthermore, dark current and electrochemical impedance spectra (EIS) of device E revealed an enhanced electron transport rate in the formic acid treated TiO2 photoanode, suppressed electron recombination at the photoanode/dye/electrolyte interface, as well as shorter electron transport time (tau(d)), and longer electron lifetime (tau(e)).
    Organic Electronics 07/2014; 15(7). DOI:10.1016/j.orgel.2014.03.033 · 3.68 Impact Factor
  • DAE‐BRNS Conference on Organic Devices: The Future Ahead (ODeFA-2014), Bhabha Atomic Research Centre, Mumbai, India; 03/2014
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    ABSTRACT: We have designed and synthesized four new metal free D–A–π–A type dyes (9–12) with variations in their acceptor/anchor groups. The four dyes carry tert-butyl substituted triphenylamine as donor, thiadiazole as acceptor and bithiophene as π-spacer. Cyanoacetic acid, rhodanine-3-acetic acid, 2-(4-methoxyphenyl)acetic acid and 2-phenylacetic acid are used as acceptor/anchor groups, respectively in the dyes 9–12. The acceptor/anchor effect on their photophysical, electrochemical and photovoltaic properties was investigated. The dyes exhibited good power conversion efficiency ranging from 1.95–4.12%. Among the four dyes, 9 showed the best photovoltaic performance: short-circuit current density (Jsc) of 8.50 mA cm−2, open-circuit voltage (Voc) of 645 mV and fill factor (FF) of 0.75, corresponding to an overall conversion efficiency of 4.12% under standard global AM 1.5 solar light conditions.
    RSC Advances 02/2014; DOI:10.1039/C3RA47330A · 3.71 Impact Factor
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    ABSTRACT: The enantiomeric differentiation of a series of chiral β-amino alcohols (A) is attempted, for the first time, by applying the kinetic method using L-proline, L-tryptophan, 4-iodo-L-phenylalanine or 3, 5-diiodo-L-tyrosine as the chiral references (Ref) and Cu(2+) or Ni(2+) ion (M) as the central metal ion. The trimeric diastereomeric adduct ions, [M+(Ref)2 +A-H](+) , formed under electrospray ionization conditions, are subjected for collision-induced dissociation (CID) experiments. The products ions, formed by the loss of either a reference or an analyte, detected in the CID spectra are evaluated for the enantiomeric differentiation. All the references showed enantiomeric differentiation and the Rchiral values are better for the aromatic alcohols than for aliphatic alcohols. Notably, the Rchiral values of the aliphatic amino alcohols enhanced when Ni(2+) is used as the central metal ion. The experimental results are well supported by computational studies carried out on the diastereomeric dimeric complexes. The computational data of amino alcohols is correlated with that of amino acids to understand the structural interaction of amino alcohols with reference molecule and central metal ion and their role on the stabilization of the dimeric complexes. Application of flow injection MS/MS method is also demonstrated for the enantiomeric differentiation of the amino alcohols. Copyright © 2014 John Wiley & Sons, Ltd.
    Journal of Mass Spectrometry 01/2014; 49(1):108-16. DOI:10.1002/jms.3312 · 2.71 Impact Factor
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    ABSTRACT: Two-photon absorption Excited state absorption Carbazole Fluorene Bis(carbazolylefluorenyl) arenes Two-photon excited fluorescence a b s t r a c t This article reports the design and synthesis of five new donor-p-acceptor-p-donor derivatives where carbazolylfluorenyl serves as donor; arenes serve as central core acceptors, and acetylene group as a p bridge. Comprehensive one-and two-photon absorption properties of these compounds were studied experimentally and theoretically. The two-photon absorption cross-sections were measured by using two-photon excited fluorescence spectrometer and showed significant enhancement from 560 to 2600 GM. In general, the two-photon absorption cross-section values increase with respect to the strength of the acceptor bridge (arenes) in the order of benzene < thiophene < fluorene < anthracene < benzothiadiazole and with the increase of excited state transition dipole moments. The calculated two-photon absorption cross-section values and trends are in good agreement with the experimental results. The combination of large two-photon absorption cross-sections and high emission quantum yields makes the dyes attractive for applications involving two-photon excited fluorescence.
    Dyes and Pigments 01/2014; 113:682-691. DOI:10.1016/j.dyepig.2014.09.027 · 3.47 Impact Factor
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    ABSTRACT: In this work, we present a detailed analysis on electron transport studies of 9,10-bis(2-phenyl-1,3,4-oxadiazole) derivatives of anthracene (OXD-PH, OXD-PTOL and OXD-OTOL). The effect of methyl substitution at ortho (OXD-OTOL) and para position (OXD-PTOL) on the phenyl ring on the electron transport properties was studied and the results were compared with the anthracene derivative without any substitution at the phenyl ring. Electron transport was found to be highly dependent on the methyl substitution and electron mobilities in OXD-PTOL and OXD-OTOL were found to be lower than in OXD-PH. Mobilities were also found to be different for OXD-PTOL and OXD-OTOL, which indicates that the substitution at different places did not have a similar effect on charge transport properties. Thickness dependent trap states were observed for all three molecules with thickness dependent electron mobilities. Electron mobility was found to increase in all three molecules with the decrease in thickness, which favors their use for organic electronic devices and all three molecules had a better electron transport in comparison to Alq3. These results were explained by the DFT calculation which showed a dihedral structure. The dihedral angle was found to reduce in the anionic form of these molecules. Therefore, these molecules are likely to favor a proper stacking in the solid state form.
    RSC Advances 01/2014; 4(24):12206. DOI:10.1039/c3ra47215a · 3.71 Impact Factor
  • OEMD - 2013, National Institute of Technology Karnataka, Surathkal; 12/2013
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    ABSTRACT: Six novel anthracene-oxadiazole derivatives, (2-(4-(anthracen-9-yl)phenyl)-5-p-tolyl-1,3,4-oxadiazole), (2-(4-(anthracen-9-yl)phenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole), (2-(4-(anthracen-9-yl)phenyl)-5-(4-methoxyphenyl)-1,3,4-oxadiazole), (2-(4-(anthracen-9-yl)phenyl)-5-m-tolyl-1,3,4-oxadiazole), (2-(3-(anthracen-9-yl)phenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) and (2-(3-(anthracen-9-yl)phenyl)-5-(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazole) have been synthesized and characterized for use as emitters in organic light emitting devices (OLEDs). They show good thermal stability (Td, 297-364 °C) and glass transition temperatures (Tg) in the range of 82-98 °C, as seen from the thermo gravimetric analysis and differential scanning calorimetric studies. The solvatochromism phenomenon and electrochemical properties have been studied in detail using UV-Vis absorption, fluorescence spectroscopy and cyclic voltammetry. TD-DFT calculations have been carried out to understand the electrochemical and photophysical properties. The spatial structures of and are further confirmed by X-ray diffraction analysis. Un-optimized non-doped electroluminescent devices were fabricated using these anthracene derivatives as emitters with the following device configuration: ITO (120 nm)/α-NPD (30 nm)/ or (35 nm)/BCP (6 nm)/Alq3 (28 nm)/LiF (1 nm)/Al (150 nm). Among all the six compounds, displays the maximum brightness of 1728 cd m(-2) and current efficiency 0.89 cd A(-1). Furthermore, as an electron transporter, exhibited superior performance (current efficiency is 11.7 cd A(-1)) than the device using standard Alq3 (current efficiency is 8.69 cd A(-1)), demonstrating its high potential for employment in OLEDs. These results indicate that the new anthracene-oxadiazole derivatives could play an important role in the development of OLEDs.
    Photochemical and Photobiological Sciences 12/2013; 13(2). DOI:10.1039/c3pp50284h · 2.94 Impact Factor
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    ABSTRACT: A series of five new ruthenium [3 + 2 + 1] complexes coded as MC107–MC111, with novel unsymmetrical bipyridines as ancillary ligands and terpyridine tricarboxylic acid as an anchoring ligand have been successfully synthesized and characterized by 1 H NMR, 13 C NMR and UV-Visible spectrometry. Improvement in the molar extinction coefficient of all these sensitizers was observed compared with reference standard N749 dye under comparable conditions. Among all the new sensitizers MC108 exhibited a maximum solar to electrical conversion efficiency of 5.573% (J sc ¼ 16.81 mA cm À2 , V oc ¼ 0.50 V. FF ¼ 0.65) under standard global AM 1.5 G solar condition, when compared to the N749 dye with an efficiency of 6.29% (J sc ¼ 13.74 mA cm À2 , V oc ¼ 0.67 V. FF ¼ 0.68) under similar fabrication and evaluation conditions. Density functional theory (DFT) and time-dependent DFT calculations are carried out for MC107–MC111 to understand their structural, electronic and photophysical properties.
    RSC Advances 09/2013; 3(48):26035–26046. DOI:10.1039/c3ra44688c · 3.71 Impact Factor
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    ABSTRACT: New low bandgap small molecules based on a squaraine (SQ) chromophore, bis[4-(2,6-di-tert-butyl)vinylpyrylium]squaraine (), bis[2,6-di-tert-butyl-4-(prop-1-en-2-yl)pyrylium]squaraine () and bis[4-(but-1-en-2-yl)-2,6-di-tert-butylpyrylium]squaraine (), were synthesized and used as electron donors along with PC70BM for their application in solution processed organic bulk-heterojunction (OBHJ) solar cell (SC). The long wavelength of these SQ dyes are located in between 650-750 nm in thin films and the optical bandgaps are about 1.64, 1.52 and 1.48 eV, respectively. The electrochemical properties of these SQ dyes indicate that they are well suited for the fabrication of OBHJSCs as electron donors along with fullerene derivatives as electron acceptors. The OBHJ photovoltaic (PV) devices fabricated with the blend of :PC70BM, :PC70BM and :PC70BM cast from chloroform (CF) solvent exhibited a power conversion efficiency (PCE) of 1.71%, 2.15%, and 1.89%, respectively. The PCE of the OBHJSCs based on :PC70BM blends cast from DIO-THF (DIO = 1,8-diiodooctane) additive solvent and cast from DIO-THF with subsequent thermal annealing have been further improved up to 2.73% and 3.14%, respectively. This enhancement in the PCE is attributed to the improvement in the crystalline nature of the blend and more balanced charge transport resulting from the higher hole mobility. All these results have been supported by the quantum chemical calculations.
    Photochemical and Photobiological Sciences 06/2013; 12(9). DOI:10.1039/c3pp50087j · 2.94 Impact Factor

Publication Stats

850 Citations
278.96 Total Impact Points

Institutions

  • 1994–2015
    • Indian Institute of Chemical Technology
      • • Molecular Modelling Group (IICT)
      • • Inorganic and Physical Chemistry Division (IICT)
      • • Natural Products Chemistry Group (IICT)
      Bhaganagar, Telangana, India
  • 2014
    • New Delhi Institute of Management
      Old Delhi, NCT, India
  • 2006
    • Vikram Sarabhai Space Centre
      Tiruvananantapuram, Kerala, India