Browsing by Author "Vishnumurthy, K.A."

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Design and synthesis of a new thiophene based donor-acceptor type conjugated polymer with large third order nonlinear optical activity
(2011) Vishnumurthy, K.A.; Vasudeva Adhikari, A.V.; Sunitha, M.S.; Ann Mary, K.A.A.; Philip, R.
In this communication we describe the design and synthesis of a new conjugated polymer (P) carrying 3,4-dialkoxythiophene, 1,3,4-oxadiazole and thienylene-vinylene units, from its monomers using Wittig condensation method. The structure of newly synthesized polymer was confirmed by FT-IR, 1H NMR, UV-vis spectral, elemental analysis and gel permeation chromatographic techniques. The polymer exhibited good thermal stability with the onset decomposition temperature around 320 °C in nitrogen atmosphere. Further, its electrochemical, linear and nonlinear optical properties have been investigated. The optical and electrochemical band gap was found to be 2.21 eV. Its third-order nonlinear optical property was investigated by Z-scan and DFWM techniques, using a Q-switched, frequency doubled Nd:YAG laser producing 7 ns laser pulses at 532 nm. Z-scan results reveal that the polymer exhibits self-defocusing nonlinearity. The operating mechanism involves reverse saturable absorption. The polymer shows strong optical limiting behavior due to effective two-photon absorption (2PA). The value of 2PA coefficient was found to be 3.0 × 10-11 mW, which is comparable to that of good optical limiting materials. The fluorescence quantum yield of the polymer in solution was determined using quinine sulfate as standard and it was found to be 35%. © 2011 Elsevier B.V. All rights reserved.
Electrochemical and nonlinear optical studies of new D-A type ?-conjugated polymers carrying 3,4-benzyloxythiophene, oxadiazole, and 3,4-alkoxythiophene systems
(2012) Sunitha, M.S.; Vasudeva Adhikari, A.V.; Vishnumurthy, K.A.; Smijesh, N.; Philip, R.
We investigated the nonlinear optical (NLO) properties of two newly synthesized conjugated polymers Pl and P2 carrying 1,3,4-oxadiazole, 3,4-dibenzyloxythiophene, and 3,4-dialkoxythiophene moieties along the main chain, as potential NLO active materials. Their structures have been well characterized. The nonlinear measurements were performed by Z-scan using 532 nm, 7 ns laser pulses. Calculated values of figure of merit and ? follow the criteria for good NLO materials. These results suggest that polymers are promising materials for applications in photonics.© 2012 The Chemical Society of Japan.
Extraction, characterization and biological studies of phytochemicals from Mammea suriga
(Xi'an Jiaotong University, 2015) Poojary, M.M.; Vishnumurthy, K.A.; Vasudeva Adhikari, A.V.
Abstract The present work involves extraction of phytochemicals from the root bark of a well-known Indian traditional medicinal plant, viz. Mammea suriga, with various solvents and evaluation of their in vitro antimicrobial and antioxidant activities using standard methods. The phytochemical analysis indicates the presence of some interesting secondary metabolites like flavonoids, cardiac glycosides, alkaloids, saponins and tannins in the extracts. Also, the solvent extracts displayed promising antimicrobial activity against Staphylococcus aureus, Bacillus subtilis and Cryptococcus neoformans with inhibition zone in a range of 20-33 mm. Further, results of their antioxidant screening revealed that aqueous extract (with IC50 values of 111.51±1.03 and 31.05±0.92 ?g/mL in total reducing power assay and DPHH radical scavenging assay, respectively) and ethanolic extract (with IC50 values of 128.00±1.01 and 33.25±0.89 ?g/mL in total reducing power assay and DPHH radical scavenging assay, respectively) were better antioxidants than standard ascorbic acid. Interestingly, FT-IR analysis of each extract established the presence of various biologically active functional groups in it. © 2015 Xi'an Jiaotong University.
Large third-order nonlinearity of new ?-conjugated donor-acceptor polymers with substituted thiophene and 1,3,4-oxadiazole moieties
(2012) Sunitha, M.S.; Vasudeva Adhikari, A.V.; Vishnumurthy, K.A.; Safakath, K.; Philip, R.
We present the synthesis of two newly designed, thiophene-based conjugated polymers (P1 and P2) carrying 1,3,4-oxadiazole, 3,4-dinaphthyloxy thiophene, and 3,4-dialkoxy thiophene moieties as potential NLO active materials. Their NLO properties have been investigated both by the Z-scan and degenerate four-wave mixing (DFWM) techniques using 532nm, 7 nanosecond laser pulses. The measured ? and ?(3) values for the polymers are found to be in the range of 1011m/W and 1011esu, respectively. The results indicate that they exhibit good optical-limiting behavior and are promising materials for nonlinear optical applications due to effective two-photon absorption (TPA). © 2012 Copyright Taylor and Francis Group, LLC.
New diphenylamine-based donor-acceptor-type conjugated polymers as potential photonic materials
(2011) Vishnumurthy, K.A.; Sunitha, M.S.; Philip, R.; Vasudeva Adhikari, A.V.
A new series of donor-acceptor-type conjugated polymers (P1 and P2) carrying a diphenyl amine moiety were synthesized via Wittig condensation technique. The polymers structures were well established by FT-IR, 1H NMR, elemental analysis and gel permeation chromatographic techniques. They exhibited good thermal stability with an onset decomposition temperature of approximately 325 °C under nitrogen atmosphere. The optical and electrochemical properties of the polymers were studied by UV-vis, fluorescence emission spectroscopy and cyclic voltammetry. They exhibited good fluorescence in dilute solutions and showed solvatochromic behavior in various polar solvents. The electrochemical studies revealed that the polymers possess low-lying LUMO energy levels that ranging from -3.47 to -3.73 eV and high-lying HOMO energy levels that ranging from -5.57 to -5.81 eV. The thirdorder nonlinear optical properties of the polymers were investigated using the Z-scan technique. The effective two-photon absorption (TPA) coefficients (?) of the polymers were found to be 0.645 × 10-10 and 0.212 × 10-10 m/W. © 2011 Elsevier Ltd. All rights reserved.
New optical limiting polymeric materials with different ?-electron conjugation bridge structures: Synthesis and characterization
(2012) Vishnumurthy, K.A.; Sunitha, M.S.; Vasudeva Adhikari, A.V.
In this communication we describe the design and synthesis of five new conjugated polymers (P1-P5) with various ?-electron conjugation bridges. Their structures were established by FTIR, 1H NMR spectroscopy, elemental analysis. The molecular weights of the polymers were estimated by gel permeation chromatographic technique. Further, their electrochemical, linear and nonlinear optical properties were investigated. The electrochemical band gaps of P1-P5 were found to be 1.72-2.35 eV. Their third-order nonlinear optical activities were studied by open aperture Z-scan technique, using a Q-switched, frequency doubled Nd:YAG laser producing 7 nano second laser pulses at 532 nm. Z-scan results reveal that the polymers exhibit self-defocusing nonlinearity and their operating mechanism involves reverse saturable absorption. The polymers showed strong optical limiting behavior due to effective two-photon absorption (2PA) with 2PA coefficients of the order of 10 -11 m/W, which is comparable to that of good optical limiting materials in the literature. © 2012 Elsevier Ltd. All rights reserved.
Nonlinear optical properties of a newly synthesized thiophene based conjugated polymer
(2011) Sunitha, M.S.; Adhikari, A.V.; Vishnumurthy, K.A.; Philip, R.
We have synthesized a new donor-acceptor (D-A) conjugated polymer containing 3,4-aralkyloxy and alkoxy substituted thiophene and 1,3,4-oxadiazole as donor and acceptor moieties respectively, through precursor polyhydrazide route. The required polyhydrazide was synthesized from 3,4-dihydroxythiophene diester through multistep reaction. The new polymer was characterized by using FTIR, 1H NMR spectroscopy, followed by Elemental analysis. The average molecular weight of the polymer was determined by Gel Permeation Chromatography. The band gap of the polymer was calculated by using UV-visible and cyclic voltametry. Further, its NLO properties in THF solution were investigated both by the Z-scan and degenerate four-wave mixing (DFWM) techniques using 532 nm, 7 nanosecond laser pulses. The results indicate that they exhibit good optical limiting behavior due to effective two-photon absorption (TPA). Values of the effective TPA coefficient (?), third-order non-linear optical susceptibility (?(3)) and figure of merit (F) were calculated. The optical and electrochemical properties reveal that the polymer is a promising candidate for opto-electronic applications. � 2011 American Institute of Physics.
Nonlinear optical properties of a newly synthesized thiophene based conjugated polymer
(2011) Sunitha, M.S.; Vasudeva Adhikari, A.V.; Vishnumurthy, K.A.; Philip, R.
We have synthesized a new donor-acceptor (D-A) conjugated polymer containing 3,4-aralkyloxy and alkoxy substituted thiophene and 1,3,4-oxadiazole as donor and acceptor moieties respectively, through precursor polyhydrazide route. The required polyhydrazide was synthesized from 3,4-dihydroxythiophene diester through multistep reaction. The new polymer was characterized by using FTIR, 1H NMR spectroscopy, followed by Elemental analysis. The average molecular weight of the polymer was determined by Gel Permeation Chromatography. The band gap of the polymer was calculated by using UV-visible and cyclic voltametry. Further, its NLO properties in THF solution were investigated both by the Z-scan and degenerate four-wave mixing (DFWM) techniques using 532 nm, 7 nanosecond laser pulses. The results indicate that they exhibit good optical limiting behavior due to effective two-photon absorption (TPA). Values of the effective TPA coefficient (Î²), third-order non-linear optical susceptibility (Ï‡(3)) and figure of merit (F) were calculated. The optical and electrochemical properties reveal that the polymer is a promising candidate for opto-electronic applications. Â© 2011 American Institute of Physics.
Photoalignment of nematic liquid crystal by thin films of bishydrazones derived from 3,4 dipropyloxythiophene
(2010) Alla, R.A.; Hegde, G.; Ravi, K.; Adhikari, A.V.; Vishnumurthy, K.A.; Komitov, L.
Photoalignment of nematic liquid crystals (LC) promoted by thin films of bishydrazone derived from 3, 4 dipropyloxythiophene is studied. Experimental results show that bishydrazone without methyl group in their structure is promoting planar alignment parallel to the polarization direction of the actinic light whereas the ones with methyl group in the structure are promoting planar alignment perpendicular to light polarization direction. � 2010 ITE and SID.
Photoalignment of nematic liquid crystal by thin films of bishydrazones derived from 3,4 dipropyloxythiophene
(2010) Alla, R.A.; Hegde, G.; Ravi, K.; Vasudeva Adhikari, A.V.; Vishnumurthy, K.A.; Komitov, L.
Photoalignment of nematic liquid crystals (LC) promoted by thin films of bishydrazone derived from 3, 4 dipropyloxythiophene is studied. Experimental results show that bishydrazone without methyl group in their structure is promoting planar alignment parallel to the polarization direction of the actinic light whereas the ones with methyl group in the structure are promoting planar alignment perpendicular to light polarization direction. Â© 2010 ITE and SID.
Poly(ionic liquid)-Based charge and size selective loose nanofiltration membrane for molecular separation
(Elsevier B.V., 2021) Naik, N.S.; Padaki, M.; Isloor, A.M.; Nagaraja, K.K.; Vishnumurthy, K.A.
Separation of chemicals using membranes in smaller size regimes is a much-complicated process. An ideal membrane for molecular separation should be more hydrophilic with well-defined pore sizes for ensuring the selectivity to give a maximum solvent flux. Here, we report a poly(itaconic acid-co-styrene-co-sulfobetaine vinylimidazole) (PIL)/PSf blend selective filtration membrane with nanochannels for superior molecular separation. FESEM images showed asymmetrical membrane structure with a dense upper layer on the hallow spherical sphere, though contact angle measurements reported improved membrane hydrophilicity. Newly developed loose nanofiltration membranes showed a superior removal performance of synthetic dyes based on their size and charge, such as congo red (2.5 × 0.7 nm2 size, 99%) and Eriochrome Black T (1.5 × 0.8 nm2 sizes, 99%). The passage of methyl orange (1.1 × 0.4 nm2) demonstrating an excellent molecular separation capability due to their stable networks of interconnected nanochannel and thin selective layer. The overall results are promising and paving the way for environmental friendly and energy-efficient separation of chemicals through membranes in industrial applications. © 2021
Recent developments in photoalignment technology: Alignment properties of a thiophene based bis-hydrazone derivative
(2012) Hegde, G.; Srivastava, A.K.; Vasudeva Adhikari, A.V.; Vishnumurthy, K.A.; Mohd Yusoff, M.M.; Chigrinov, V.G.; Kwok, H.S.
Liquid crystal photoalignment on bis-hydrazones derived from thiophene derivatives is reviewed. Proposed material shows excellent alignment properties which is highly promisable for future applications. This photoalignment is based on reorientation phenomena attributed to thiophenes.
Reduction of nitro compounds carrying electron withdrawing groups: A convenient approach without metal catalyst
(Elsevier B.V., 2019) Vishnumurthy, K.A.; Vasudeva Adhikari, A.V.
In this communication we report a convenient reduction technique for conversion of electron deficient aromatic nitro compounds to corresponding amino derivatives using hydrazine hydrate without any metal catalyst. The reduction process is carried out in different solvents under heating condition and microwave irradiation. In this method three novel substituted amines were synthesized from their respective nitro compounds with quantitative yield. Interestingly, the reduction process went smoothly without formation of any side product. The reaction is highly selective to nitro compounds without affecting ester functionality. Further it has been observed that the nature of substituent attached to nitro compound has a major role in reduction rate. As electron withdrawing nature increases the reduction takes place faster. Also it has been observed that the reaction is even faster in microwave irradiation without using of any organic solvent. The probable mechanism of reduction of nitro compound has been highlighted. Â© 2019 Elsevier B.V.
Synthesis and characterization of a new conjugated polymer bearing pyrazole and thiophene moieties as potent NLO material
(2011) Vishnumurthy, K.A.; Adhikari, A.V.; Sunitha, M.S.; Philip, R.
In this communication we describe the design and synthesis of a new conjugated polymer (P) carrying 3,4-dialkoxythiophene, 1,3,4 oxadiazole and pyrazole units, from its monomers through condensation polymerization method. The structure of newly synthesized polymer was established by FT-IR, 1H NMR, elemental analysis and gel permeation chromatographic techniques. Further, its electrochemical, linear and nonlinear optical properties of the polymer have been investigated. The optical and electrochemical band gap was found to be 2.39 eV. Z-scan results reveal that the polymer exhibits strong optical limiting behavior due to effective three-photon absorption (3PA). The value of 3PA coefficient was found to be 1.1�10-20m3/W2, which is comparable to that of good optical limiting materials. The fluorescence quantum yield of the polymer in solution was determined using quinine sulfate as standard and it was found to be 42%. � 2011 American Institute of Physics.
Synthesis and characterization of a new conjugated polymer bearing pyrazole and thiophene moieties as potent NLO material
(2011) Vishnumurthy, K.A.; Vasudeva Adhikari, A.V.; Sunitha, M.S.; Philip, R.
In this communication we describe the design and synthesis of a new conjugated polymer (P) carrying 3,4-dialkoxythiophene, 1,3,4 oxadiazole and pyrazole units, from its monomers through condensation polymerization method. The structure of newly synthesized polymer was established by FT-IR, 1H NMR, elemental analysis and gel permeation chromatographic techniques. Further, its electrochemical, linear and nonlinear optical properties of the polymer have been investigated. The optical and electrochemical band gap was found to be 2.39 eV. Z-scan results reveal that the polymer exhibits strong optical limiting behavior due to effective three-photon absorption (3PA). The value of 3PA coefficient was found to be 1.1Ã—10-20m3/W2, which is comparable to that of good optical limiting materials. The fluorescence quantum yield of the polymer in solution was determined using quinine sulfate as standard and it was found to be 42%. Â© 2011 American Institute of Physics.
Synthesis and characterization of thiophene-based donor-acceptor type polyimide and polyazomethines for optical limiting applications
(2013) Vishnumurthy, K.A.; Sunitha, M.S.; Vasudeva Adhikari, A.V.
In this communication we describe the design and synthesis of four new conjugated polymers (P1-P4) based on 3,4-ditetradecyloxythiophene. The required diamine monomer was prepared by a unique catalyst-free reduction process using hydrazine hydrate. The structures of the intermediates and polymers were established by FTIR, 1H NMR spectroscopy. Molecular weights of polymers were determined by gel permeation chromatographic (GPC) method. Their electrochemical properties were investigated by cyclic voltammetry and linear optical properties were determined by UV-Visible absorption and fluorescence emission spectroscopic techniques. Further, their nonlinear optical properties were evaluated by Z-scan technique using Nd:YAG laser. These polymers showed strong optical limiting behavior with two-photon absorption (2PA) coefficients of the order of 10-10 m/W, which are comparable to that of good optical limiting materials reported in the literature. Also, it has been observed that the optical nonlinearity enhanced with the increase in donor-acceptor strength of the polymer backbone. © 2012 Springer-Verlag.
Synthesis and two-photon absorption property of new ? -conjugated donor-acceptor polymers carrying different heteroaromatics
(2013) Sunitha, M.S.; Vishnumurthy, K.A.; Vasudeva Adhikari, A.V.
In this communication, we report the synthesis of three newly designed fluorescent polymers P1-P3, starting from simple thiophene derivatives through precursor polyhydrazide route. The new polymers, carrying donor and acceptor heterocyclic moieties with different spacer groups were found to be thermally stable and good of nonlinear optical (NLO) materials with two photon absorption property. The structures of newly synthesized monomers and polymers were confirmed by FTIR, NMR spectral and elemental analyses. Further, polymers were characterized by GPC and TGA studies. Their linear optical and electrochemical properties were evaluated by UV-vis, fluorescence spectroscopic and cyclic voltammetric (CV) studies, respectively, whereas their NLO properties were studied by Z-scan technique using Nd: YAG laser at 532 nm with 7 ns pulse. The electrochemical band gap of P1-P3 was determined to be 1.98, 1.91 and 2.05 eV, respectively. The NLO results reveal that polymers P1-P3 show good optical limiting property with TPA coefficient values 2.9 × 10 - 11 m/W, 8.0 × 10 - 11 m/W and 1.4 × 10 - 11 m/W, respectively. © 2013 Indian Academy of Sciences.
Synthesis of nonlinear heteroaromatic donor–acceptor conjugated polymers: Structural, theoretical, electrochemical, and optical properties
(John Wiley and Sons Inc, 2025) Sunitha, M.S.; Naik, P.; Vishnumurthy, K.A.; Vasudeva Adhikari, A.V.
This study presents a new class of donor–acceptor (D–A) type NLO-active polymeric materials (P1–4), bearing 3,4-disubstituted thiophene as electron donor and 1,3,4-oxadiazole as electron acceptor units, along with various aromatic spacers, namely: phenylenevinylene (P1), 3,4-ethylenedioxythiophene-EDOT (P2), naphthalene (P3), and biphenyl group (P4). Their optical and electrochemical behavior was thoroughly examined using cyclic voltammetry, UV–visible absorption spectroscopy, fluorescence emission spectroscopy, and Z-scan technique for nonlinear optical assessments. Additionally, Density Functional Theory analysis and Molecular Electrostatic Potential mapping were carried out to understand the charge distribution and electronic structure in the repeating units of polymers. The influence of the incorporated conjugated ?-linkers on their molecular geometry and optoelectronic properties was analyzed to reveal the relationship between molecular structures and optoelectronic characteristics. Interestingly, P1–4 exhibited distinctive electrochemical band gaps, and noteworthy optical limiting behavior attributed to efficient two-photon absorption, demonstrating their potential for optoelectronic and photonic applications. Among the new polymers P1–4, P2 displayed the highest two-photon absorption coefficient. Highlights: A class of D–A type polymers with varied aromatic ?-spacers were synthesized. New polymers were characterized as potential optical limiting materials. Electronic and charge distribution properties were studied by DFT and MESP. Optical and electrochemical studies showed suitability for nonlinear optics. TPA values are comparable to those typically found in top-tier NLO materials. © 2025 Society of Plastics Engineers.
Synthesis, electrochemical and optical studies of new cyanopyridine based conjugated polymers as potential fluorescent materials
(Elsevier Ltd, 2011) Vishnumurthy, K.A.; Sunitha, M.S.; Safakath, K.; Philip, R.; Vasudeva Adhikari, A.V.
In this communication we describe the design and synthesis of four new conjugated polymers (P1-P4) carrying cyanopyridine in their backbone via Wittig condensation technique. Their structures were well established by FTIR, 1H NMR, elemental analysis and gel permeation chromatographic techniques. They exhibited good thermal stability with the onset decomposition temperature around 300-350 °C in nitrogen atmosphere. Further, their electrochemical, linear and third-order non-linear optical properties have been investigated. The polymers showed low electrochemical band gaps in the range of 1.77-1.99 eV and displayed very good fluorescence emission property in various polar solvents. The fluorescence quantum yields of polymers P1-P4 in tetrahydrofuran (THF) were found to be 35, 42, 38 and 34%, respectively. The effective two-photon absorption coefficients (?) for the polymers were determined by Z-Scan technique and were found to be 1.34 × 10 -11, 1.24 × 10-11, 3.04 × 10-11 and 1.85 × 10-11 m/W for polymers P1-P4, respectively. © 2011 Elsevier Ltd. All rights reserved.
Synthesis, physicochemical properties and computational study of donor–acceptor polymer for optical limiting application
(Springer Nature, 2020) Vishnumurthy, K.A.; Girish, K.H.; Vasudeva Adhikari, A.V.
A new donor–acceptor configured ?-conjugated polymer P1 with alkoxy pendant groups having cyclic diimide and thiophene core moieties in polymer backbone were efficiently synthesized via polycondensation reaction. The incorporation of cyclic diimide in polymer increased the rigidity and thermal stability of polymer backbone aided by its high Tg value. These chromophores assisted in reducing the steric interaction of bulky alkoxy pendants which supported lowering the bandgap. The donor and acceptor moieties along with ? spacers were particularly chosen to enhance the ?-conjugation length in the polymer thereby increasing its nonlinear optical absorption i.e. two-photon absorption. The various structure–property relationships of the polymer were characterized by UV–Vis absorption, fluorescence emission, cyclic voltammetry, and density functional theory studies. The molecular nonlinear properties were theoretically evaluated through the calculation of polarizabilities and hyperpolarizabilities using time-dependent Hartree–Fock method. The polymer showed enhanced effective two-photon absorption with an absorption coefficient (?eff) of 2.031 × 10?10 m/W obtained from open aperture Z-scan analysis which is in good agreement with theoretical study. © 2020, Springer Nature Switzerland AG.