Faculty Publications
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Item 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.Item 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.Item 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.Item 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.Item 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.Item 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.Item 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.