Browsing by Author "Murali, M.G."

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Design and synthesis of new low band gap organic semiconductors for photovoltaic applications
(2014) Murali, M.G.; Dalimba, 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.
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 Â°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. Â© 2014 SPIE.
New thiophene-based donor-acceptor conjugated polymers carrying fluorene or cyanovinylene units: Synthesis, characterization, and electroluminescent properties
(John Wiley and Sons Inc, 2013) Murali, M.G.; Udayakumar, U.; Yadav, V.; Srivastava, R.
Two new thiophene-based donor-acceptor (D-A) conjugated polymers, PDTOFV and PDTOCN, are synthesized and characterized. The polymers are readily soluble in common organic solvents and exhibit good thermal stability with onset decomposition temperature (Td) in the range 310-330°C. Cyclic voltammetry studies revealed that polymers possess low-lying highest occupied molecular orbital (HOMO) energy levels (-5.94 eV for PDTOFV and -5.86 eV for PDTOCN) and low-lying lowest unoccupied molecular orbital (LUMO) energy levels (-3.35 eV for PDTOFV and -3.55 eV for PDTOCN). The optical band gap is calculated from onset absorption edge of the polymer film. The polymers exhibit green fluorescence with fluorescence quantum yields (?fl) of 38% and 42%, respectively, for PDTOFV and PDTOCN. Polymer light-emitting diodes (PLEDs) are fabricated using these polymers with a device configuration of ITO/PEDOT:PSS/polymer/Al. The device based on PDTOFV emitted green light with Commission Internationale de I'Eclairage (CIE) coordinate values of (0.25, 0.39). Whereas, the device based on PDTOCN showed white light emission with CIE coordinate values of (0.32, 0.35), which is very close to the values (0.33, 0.33) of standard white light emission. The threshold voltages of the PLEDs are determined by current density-voltage characteristics and are found to be 7.3 and 3.9 V for PDTOFV and PDTOCN, respectively. © 2012 Society of Plastics Engineers.
Synthesis and characterization of a new donor-acceptor conjugated polymer and polymer/Ag nanocomposites
(2011) Murali, M.G.; Udayakumar, D.
A 3,4-didodecyloxythiophene and (1,3,4-oxadiazolyl)benzene unit bearing a donor - acceptor (D-A) type conjugated polymer is synthesized using precursor polyhydrazide route. The optical energy band gap (Eg) of the polymer is calculated from the absorption edge in the film and is found to be 2.28 eV. To prepare polymer/Ag nanocomposites films, different wt% silver nanoparticles are used. The presence of silver nanoparticles in the nanocomposite is confirmed by field emission scanning electron microscopy (FESEM). The optical properties of the polymer and the nanocomposites are studied using UV-vis absorption spectroscopy and fluorescence emission spectroscopy. Cyclic voltammetry is used to study the electrochemical properties of the polymer. � 2011 American Institute of Physics.
Synthesis and characterization of a new donor-acceptor conjugated polymer and polymer/Ag nanocomposites
(2011) Murali, M.G.; Udayakumar, D.
A 3,4-didodecyloxythiophene and (1,3,4-oxadiazolyl)benzene unit bearing a donor - acceptor (D-A) type conjugated polymer is synthesized using precursor polyhydrazide route. The optical energy band gap (Eg) of the polymer is calculated from the absorption edge in the film and is found to be 2.28 eV. To prepare polymer/Ag nanocomposites films, different wt% silver nanoparticles are used. The presence of silver nanoparticles in the nanocomposite is confirmed by field emission scanning electron microscopy (FESEM). The optical properties of the polymer and the nanocomposites are studied using UV-vis absorption spectroscopy and fluorescence emission spectroscopy. Cyclic voltammetry is used to study the electrochemical properties of the polymer. Â© 2011 American Institute of Physics.
Synthesis and characterization of thiophene and fluorene based donor-acceptor conjugated polymer containing 1,3,4-oxadiazole units for light-emitting diodes
(2012) Murali, M.G.; Naveen, P.; Udayakumar, U.; Yadav, V.; Srivastava, R.
A new donor-acceptor (D-A) conjugated polymer (PDTOF) containing 3,4-didodecyloxythiophene, fluorene and 1,3,4-oxadiazole units is synthesized by using Wittig reaction methodology. The synthesized polymer is characterized by 1H NMR, FTIR, GPC, and elemental analysis. The optical energy band gap of the polymer is found to be 2.42 eV as calculated from the onset absorption edge. The electrochemical studies of PDTOF reveal that, the HOMO and LUMO energy levels of the polymer are -5.45 eV and -3.58 eV, respectively. The polymer is thermally stable up to 320 °C. Polymer light-emitting diode devices are fabricated with a configuration of ITO/PEDOT: PSS/PDTOF/Al using PDTOF as the emissive layer. The electroluminescence (EL) spectrum of the device showed green emission with CIE coordinate values (0.34, 0.47). By current density-voltage characteristics, threshold voltage of the PLED device is found to be 6.5 V. © 2011 Elsevier Ltd. All rights reserved.
Synthesis and study of optical properties of linear and hyperbranched conjugated polymers containing thiophene and triphenylamine units
(2014) Prashanth Kumar, K.R.; Murali, M.G.; Udayakumar, U.
We report the synthesis of solution processable donor-acceptor type conjugated monomer (M1) and polymers (P1 and P2) consisting of electron-accepting 1,3,4-oxadiazole unit and electron-donating 3,4-didecyloxythiophene, and triphenylamine units through Wittig polycondensation reaction. The linear polymer P1 is thermally stable up to 325 °C whereas the hyperbranched polymer P2 showed better thermal stability with an onset of decomposition at 375 °C. Polymer P2 showed lower band gap energy (1.96 eV) than that of P1 (2.09 eV). Polymers P1 and P2 emit yellow and orange light, respectively, under the irradiation of UV light. Electrochemical studies revealed that the polymers possess high-lying highest occupied molecular orbital and low-lying lowest unoccupied molecular orbital energy levels. Polymer light-emitting diodes are fabricated with the device configuration of ITO/PEDOT:PSS/polymer (P1 or P2)/Al. The device based on P2 showed a very low threshold voltage of 2 V. The third-order nonlinear optical properties of the polymers are studied using Z-scan technique. Both polymers showed a strong optical limiting behavior. The value of nonlinear absorption coefficient (?) of the polymers is of the order 10-10mW-1 which indicates that these materials may be accomplished for fabricating optical limiters. © 2013 Taylor & Francis.
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.
Synthesis, characterization, and nonlinear optical properties of donor-acceptor conjugated polymers and polymer/Ag nanocomposites
(2012) Murali, M.G.; Udayakumar, U.; Sridharan, K.
Two new donor-acceptor (D-A) conjugated polymers P1 and P2 containing 3,4-didodecyloxythiophene and 1,3,4-oxadiazole units are synthesized via Wittig reaction methodology. Cyclic voltammetry studies reveal that the polymers are both p and n dopable, and possess low-lying LUMO energy levels (-3.34 eV for P1 and -3.46 eV for P2) and high-lying HOMO energy levels (-5.34 eV for P1 and -5.27 eV for P2). The optical band gap of the polymers is in the range of 2.25-2.29 eV, calculated from the onset absorption edge. The polymers emit orange to yellow light in the film state when irradiated with a UV light. The synthesized polymers are used to prepare polymer nanocomposites with different wt% of silver nanoparticles. The polymer nanocomposites are characterized by UV-Vis absorption spectroscopy, field emission scanning electron microscopy, and thermogravimetric analysis. Both polymers and polymer/ Ag nanocomposites show good thermal stability with onset decomposition temperature around 300 °C under nitrogen atmosphere. The nonlinear optical properties of polymers and polymer/Ag nanocomposites are measured by Z-scan technique. Both polymers and polymer nanocomposites show a good optical limiting behavior. Nearly five times enhancement in the nonlinear optical properties is observed for polymer/Ag nanocomposites. The value of effective two-photon absorption coefficient (?) is in the order of 10 -10-10 -11 m/W. These results indicate that the synthesized polymers (P1 and P2) and their Ag nanocomposites are expected to be good candidates for application in photonic devices. © Springer Science+Business Media, LLC 2012.
Thiophene-Based Conjugated Polymers: Synthesis, Linear, and Third-Order Nonlinear Optical Properties
(CRC Press, 2016) Murali, M.G.; Udayakumar, D.
Extensive research work in the field of CPs has started in late 1970s with the discovery of electrical conductivity in oxidatively doped poly(acetylene) [1]. This important discovery led to the award of Nobel Prize in chemistry in the year 2000 to three scientists: Hideki Shirakawa, Alan G MacDiarmid, and Alan J. Heeger. This pioneering work motivated the researchers to synthesize and to study the properties of other new classes of Π-CPs based on aromatic precursors such as p-phenylenevinylene, thiophene, pyrrole, carbazole, fluorene, and their derivatives (Figure 16.2) [2-5]. Early work in this field held the hope that these types of polymer systems would serve as replacements for highly conductive metals, such as copper and aluminum for electrical transport or related applications. However, due to the instability of these systems when highly doped, other more practical uses have been realized such as polymer light-emitting diodes (PLEDs) [6-11]. Moreover, in order to tune the specific properties desired for end-user applications, a proper modification of the monomer structure is essential that manipulates both the electronic and optical properties of these polymer systems. © 2017 by Taylor and Francis Group, LLC.
Thiophene-based donor-acceptor conjugated polymer as potential optoelectronic and photonic material
(2013) Murali, M.G.; Udayakumar, U.; Yadav, V.; Srivastava, R.; Safakath, K.
In this paper, we report the synthesis, characterization and optical properties of a donor-acceptor conjugated polymer, PTh-CN, containing 3,4-didodecyloxythiophene and cyanovinylene units. The polymer possesses a low band gap of 1.75 eV as calculated from the onset absorption edge. From the electrochemical study, the HOMO and LUMO energy levels of the polymer are figured out to be -5.52 eV and -3.52 eV, respectively. Polymer light-emitting diodes are fabricated using PTh-CN as the emissive layer with a device configuration of ITO/PEDOT:PSS/PTh-CN/Al. The device showed stable saturated red electroluminescence with CIE coordinate values (0.65, 0.32) at 12 V, which are very close to the values for standard red demanded by the NTSC. In addition, the device showed good colour stability under different bias voltages and the threshold voltage of the PLED device is found to be as low as 3.1 V. Further, a nanocomposite of the polymer and TiO2 nanoparticles is prepared by the dispersion method. The nonlinear optical properties of PTh-CN and PTh-CN/TiO 2 nanocomposite are studied using z-scan technique. The polymer solution, polymer film and polymer/TiO2 nanocomposite film show a strong saturable absorption behaviour. The value of saturation intensity (I s) is found to be of the order 1011-1012 W/m2, indicating that the materials are useful candidates for photonic applications. [Figure not available: see fulltext.] © 2013 Indian Academy of Sciences.