Faculty Publications

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Subject: search.filters.subject.Conjugated polymers

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Now showing 1 - 10 of 33
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    Design and synthesis of new low band gap organic semiconductors for photovoltaic applications
    (SPIE spie@spie.org, 2014) Murali, M.G.; Udayakumar, U.K.
    Donor-acceptor (D-A) conjugated polymers have attracted a good deal of attention in recent years. In D-A systems, the introduction of electron withdrawing groups reduces Eg by lowering the LUMO levels whereas, the introduction of electron donating groups reduces Eg by raising the HOMO levels. Also, conjugated polymers with desired HOMO and LUMO energy levels could be obtained by the proper selection of donor and acceptor units. Because of this reason, D-A conjugated polymers are emerging as promising materials particularly for polymer light emitting diodes (PLEDs) and polymer solar cells (PSCs). We report the design and synthesis of four new narrow band gap donor-acceptor (D-A) conjugated polymers, PTCNN, PTCNF, PTCNV and PTCNO, containing electron donating 3,4-didodecyloxythiophene and electron accepting cyanovinylene units. The effects of further addition of electron donating and electron withdrawing groups to the repeating unit of a D-A conjugated polymer (PTCNN) on its optical and electrochemical properties are discussed. The studies revealed that the nature of D and A units as well as the extent of alternate D-A structure influences the optical and the electrochemical properties of the polymers. All the polymers are thermally stable up to a temperature of 300 °C under nitrogen atmosphere. The electrochemical studies revealed that the polymers possess low-lying HOMO energy levels and low-lying LUMO energy levels. In the UV-Vis absorption study, the polymer films displayed broad absorption in the wavelength region of 400-700 nm. The polymers exhibited low optical band gaps in the range 1.70 - 1.77 eV. © 2014 SPIE.
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    Synthesis and characterization of fluorescent poly(oxadiazole)s containing 3,4-dialkoxythiophenes
    (Elsevier, 2007) Udayakumar, D.; Vasudeva Adhikari, A.V.
    We report the synthesis, optical and electrochemical details, and properties of three conjugated copolymers (P1-P3) consisting of alternate hole-transporting thiophene derivative and electron-transporting 1,3,4-oxadiazole units. The polymers are prepared using the precursor polyhydrazide route. The polymers have well defined structure and exhibit good thermal stability with the onset decomposition temperature in nitrogen at around 300 °C. All the polymers are soluble in organic solvents such as DMF, DMSO, NMP and in strong organic acids like trifluoroacetic acid. The optical and charge-transporting properties of the polymers are investigated by UV-visible spectroscopy, fluorescence emission spectroscopy and cyclic voltammetry. The UV-visible absorption spectra of polymers in solution showed a maximum at around 400 nm. The polymers depicted green fluorescence both in solution and as thin films. Cyclic voltammetry studies reveal that these copolymers have low-lying LUMO energy levels ranging from -3.28 to -3.36 eV and high-lying HOMO energy levels ranging from -5.5 to -5.56 eV, which indicated that they may be promising candidates for electron-transporting or hole-blocking materials in light-emitting diodes. © 2006 Elsevier B.V. All rights reserved.
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    Third-order nonlinear optical studies of newly synthesized polyoxadiazoles containing 3,4-dialkoxythiophenes
    (2006) Udayakumar, D.; John Kiran, A.; Vasudeva Adhikari, A.V.; Chandrasekharan, K.; Umesh, G.; Shashikala, H.D.
    The third-order nonlinear optical properties of newly synthesized soluble polyoxadiazoles containing 3,4-dialkoxythiophenes were investigated by using Z-scan and degenerate four-wave mixing (DFWM) techniques. The measurements were performed at 532 nm with 7 ns pulses from a Nd:YAG laser. We found a good agreement between the values of ?(3) determined from both the experiments. Z-scan results indicate a negative nonlinear refractive index, n2, whose magnitude is of the order of 10-10 esu for all the copolymers. The variation of nonlinear response among the copolymers clearly indicates the dependence of ?(3) on donor and acceptor type of units present in these copolymers. The copolymers exhibit strong reverse saturable absorption and good optical limiting properties at 532 nm. © 2006 Elsevier B.V. All rights reserved.
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    Synthesis and characterization of novel conjugated copolymers containing 3,4-dialkoxythiophene and 1,3,4-oxadiazole units
    (2007) Udayakumar, D.; Vasudeva Adhikari, A.V.
    In this report we describe the synthesis, optical and electrochemical properties of new conjugated copolymers (P1-P4) based on 3,4-dialkoxythiophene and 1,3,4-oxadiazole units. The copolymers are prepared using the precursor polyhydrazide route. The chemical structures of the copolymers are confirmed using FTIR, NMR spectroscopy and CHNS analysis. The polymers exhibit good thermal stability with the onset decomposition temperature in nitrogen at around 300 °C. The optical and charge-transporting properties of the copolymers are investigated by UV-visible absorption spectroscopy, fluorescence emission spectroscopy and cyclic voltammetry. The polymers depicted blue/green fluorescence under the irradiation of UV light. Cyclic voltammetry studies reveal that these copolymers have low-lying LUMO energy levels ranging from -3.28 to -3.32 eV and high-lying HOMO energy levels ranging from -5.26 to -5.62 eV, which indicated that they may be promising candidates for the fabrication of polymer light-emitting diodes. In addition, the copolymers showed good third-order non-linear optical properties. © 2007 Elsevier Ltd. All rights reserved.
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    Synthesis and nonlinear optical characterization of copolymers containing alternating 3,4-dialkoxythiophene and 1,3,4-oxadiazolydbenzene units
    (2007) Udayakumar, D.; Kiran, A.J.; Vasudeva Adhikari, A.V.; Chandrasekharan, K.; Shashikala, H.D.
    We report the synthesis and linear and third-order nonlinear optical (NLP) characterization of two novel copolymers containing alternating 3,4-dialkoxythiophene and 1,4-bis(1,3,4-oxadiazolyl)benzene units. The copolymers were synthesized with a precursor polyhydrazide route. Both copolymers exhibited fluorescence around 430 nm under the irradiation of UV light. The NLO measurements were made with the single-beam Z-scan technique with Nd:YAG nanosecond laser pulses at 532 nm. The nonlinear refractive index of the investigated copolymers was negative, and the magnitude was as high as 10 -10 esu. The samples exhibited strong reverse saturation absorption and very good optical limiting properties at the wavelength used. The concentration dependence of third-order NLO parameters was studied. ©2007 Wiley Periodicals, Inc.
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    Nonlinear optical studies on a new poly{2-(biphenyl-4-yl)-5-[3,4- didecyloxy-5-(1,3,4-oxadiazol-2-yl)thiophen-2-yl]-1,3,4-oxadiazole}
    (Trans Tech Publications Ltd ttp@transtec.ch, 2010) Hegde, P.K.; Vasudeva Adhikari, A.V.; Manjunatha, M.G.; Suchand Sandeep, C.S.; Philip, R.
    Measurements of nonlinear optical properties of a newly synthesized thiophene based polymer are reported. The nonlinear transmission measurements were performed on the polymer dissolved in N,N-dimethylformamide by employing the single beam Z-scan technique using a Q-switched laser output at 532-nm. The polymer shows strong optical limiting behavior, where the transmittance decreases when the pump fluence is increased. It was found that an effective three-photon absorption (3PA) model at the excitation wavelength gives the best fit to the obtained experimental data. The value of the 3PA coefficient has been numerically calculated. This study clearly reveals the potential of new polymeric material has, for optical limiting applications. © (2010) Trans Tech Publications.
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    Electrochemical and optical properties of a new donor-acceptor type conjugated polymer derived from 3,4-didodecyloxythiophene
    (Indian Academy of Sciences, 2010) Hegde, P.K.; Vasudeva Adhikari, A.V.; Manjunatha, M.G.
    In this communication, we report the synthesis and characterization of a new donor-acceptor type conjugated polymer carrying alternate 3,4-didodecyloxythiophene and (1,3,4-oxadiazol-yl)pyridine moieties and evaluation of its optical and electrochemical properties. The polymer was synthesized through precursor polyhydrazide route. It has well defined structure, stability and it shows good solubility in common organic solvents. Optical and electrochemical properties were studied by UV-visible, fluorescence spectroscopy and cyclic voltammetric studies, respectively. It displays bluish-green fluorescence both in solution and in film state. Cyclic voltammetric studies showed that the polymer P1 possesses a HOMO energy level of -6-01 and LUMO energy level of -3-34 eV. The preliminary studies clearly reveal that the new polymer can have potential application in the fabrication of light emitting diodes. The studies on its device application are in progress. © Indian Academy of Sciences.
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    Optical and electrochemical properties of a new donor-acceptor type conjugated polymer derived from thiophene, carbazole and 1,3,4-oxadiazole units
    (Trans Tech Publications Ltd ttp@transtec.ch, 2010) Manjunatha, M.G.; Vasudeva Adhikari, A.V.; Hegde, P.K.
    A new donor-acceptor type poly[3-{5-[3,4-didecyloxy-5-(1,3,4-oxadiazol-2- yl)thiophen-2-yl]-1,3,4-oxadiazol-2-yl}-9-dodecyl-9H-carbazole] (P) has been synthesized starting from thiodiglycolic acid and 9H-carbazole through multistep reactions. The polymer has been synthesized through precursor polyhydrazide route. The weight average molecular weight of the polymer was found to be 7210. The polymer exhibited intense green fluorescence in solid sate. Cyclic voltammetric experiments showed that the polymer has low-lying LUMO (-3.55 eV) and high lying HOMO (-5.77 eV) energy levels due to the presence of alternate donor and acceptor units. The optical and electrochemical studies reveal that the new polymer (P) is a promising material for the development of polymer light emitting diodes (PLEDs). © (2010) Trans Tech Publications.
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    Synthesis and characterization of a new NLO-active donor-acceptor-type conjugated polymer derived from 3,4-diphenylthiophene
    (2010) Manjunatha, M.G.; Vasudeva Adhikari, A.V.; Hegde, P.K.; Suchand Sandeep, C.S.; Philip, R.
    A new donor-acceptor-type conjugated polymer (P1) carrying 3,4-diphenylthiophene, 2,5-dihexyloxybenzene, and 1,3,4-oxadiazole units was synthesized through multistep reactions. The polymer was prepared using a polyhydrazide precursor route. The polymer has a well-defined structure and exhibits good thermal stability, with a decomposition onset temperature in nitrogen of 300 °C. Cyclic voltammetry experiments revealed that the polymer has low-lying LUMO (-3.68 eV) and high-lying HOMO (-5.78 eV) energy levels. The electrochemical band gap was found to be 2.10 eV. The UV-visible absorption spectrum of the polymer presented a maximum at 373 nm, and it displayed bluish-green fluorescence in dilute chloroform solution. The nonlinear optical properties of the new polymer were investigated at 532 nm using the Z-scan technique with nanosecond laser pulses. The polymer exhibited strong optical limiting behavior due to excited state absorption, which was phenomenologically similar to a three-photon absorption (3PA) process. The 3PA coefficient ? was found to be 7×10-22 m3/W2. The studies show that the new polymer (P1) is a promising material for developing efficient photonic devices.
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    Synthesis and third order optical nonlinearity studies of the donor-acceptor conjugated polymer, poly(2-[3,4-didodecyloxy-5-(1,3,4-oxadiazol- 2-yl)thiophen-2-yl]-5-phenyl-1,3,4-oxadiazole) and a polymer/TiO2 nanocomposite
    (2010) Murali, M.G.; Ramya, M.G.; Udayakumar, D.; Lakshmi, N.B.; Philip, R.
    A donor-acceptor conjugated polymer (PDOThPOD) containing 3,4-didodecyloxythiophene and (1,3,4-oxadiazolyl)benzene units is synthesized by using precursor polyhydrazide route. Cyclic voltammetry studies reveal that the polymer possesses a low-lying LUMO energy level (-3.57 eV). A nanocomposite of polymer PDOThPOD and nano TiO2 is also prepared. The linear optical properties of PDOThPOD and the nanocomposite are studied using UV-vis absorption spectroscopy and fluorescence emission spectroscopy. z-scan technique is used to study the third order nonlinear optical properties of the polymer and nanocomposite films. Both polymer and nanocomposite films show a strong optical limiting behavior. The value of nonlinear absorption coefficient (?) is found to be of the order of 10-7 m/W, indicating that these materials are potentially suited for fabricating optical limiters. © 2010 Elsevier B.V. All rights reserved.