Faculty Publications
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Item Structure-Property Evaluation of Knoevenagel-Derived π-Conjugated Organic Systems(John Wiley and Sons Inc, 2025) Ravikumar, M.V.; Raj, A.K.; Rajeswara Rao, M.; Lakshmi, V.π-Conjugated organic compounds display unique optical and electrical properties, rendering them appropriate for semiconducting applications. Knoevenagel condensation is one of the important reactions that facilitate the formation of olefin linkages (−C=C−) and thus has been widely employed to synthesize new π-conjugated molecules. This review summarizes the synthesis of π-conjugated compounds constructed using four novel π-conjugated moieties: diketonate/azopyrrole-BF2 complexes (BF), p-azaquinodimethane (AQM), diketopyrrolopyrrole (DPP), and barbituric acid (BA), alongside their optoelectronic features and applications in sensing, bioimaging, and photovoltaic technologies. © 2025 Wiley-VCH GmbH.Item Synthesis and characterization of new light-emitting copolymers containing 3,4-dialkoxythiophenes(2006) Udayakumar, D.; Vasudeva Adhikari, A.V.We report the synthesis, optical and electrochemical properties of a new series of polyoxadiazoles (P1-P3) consisting of 3,4-dialkoxythiophene and 1,4-divinylbenzene 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 330 °C. The optical and charge-transporting properties of the polymers are investigated by UV-vis spectroscopy, fluorescence emission spectroscopy and cyclic voltammetry. The UV-vis absorption spectra of polymers in solution showed a maximum at around 380 nm. The polymers depicted bluish-green fluorescence in solutions and green fluorescence in thin films. Cyclic voltammetry studies reveal that these copolymers have low-lying LUMO energy levels ranging from 3.25 to 3.31 eV and HOMO energy levels ranging from 5.48 to 5.56 eV, which indicated that the polymers are expected to provide enhanced charge-transporting (electron transport/hole blocking) properties for the development of efficient polymer light-emitting diodes (PLEDs). © 2006 Elsevier B.V. All rights reserved.Item 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.Item 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.Item 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.Item Third-order nonlinear optical susceptibilities of new copolymers containing alternate 3,4-dialkoxythiophene and (1,3,4-oxadiazolyl)pyridine moieties(Elsevier, 2009) Hegde, P.K.; Vasudeva Adhikari, A.V.; Manjunatha, M.G.; Poornesh, P.; Umesh, G.A new series of conjugated copolymers (P1-P3) consisting of alternate 3,4-dialkoxythiophene and (1,3,4-oxadiazolyl)pyridine moieties have been synthesized using the precursor polyhydrazide route. They have been characterized by FTIR, 1H NMR spectral and elemental analyses. These copolymers possess well defined structure and exhibit good thermal stability with the onset decomposition temperature in nitrogen at around 300 °C. Their molecular weights were determined by gel permeation chromatography (GPC). The optical and charge-transporting properties of the copolymers were investigated by UV-visible spectroscopy, fluorescence emission spectroscopy and cyclic voltammetry. Their UV-visible absorption spectra showed a ?max at around 342 nm and displayed bluish-green fluorescence in solution state. The band gaps were found to be at about 2.55 eV for all the copolymers. The third-order nonlinear optical properties (NLO) of these copolymers were studied by Z-scan technique. The measurements were performed at 532 nm with 7 ns laser pulses using a Nd:YAG laser in solution form. The real part of ?(3) were estimated to be -0.881 × 10-12, -0.901 × 10-12 and -1.030 × 10-12 esu for P1, P2 and P3 respectively. The imaginary part of ?(3) for the copolymers P1, P2 and P3 were determined to be 0.192 × 10-12, 0.253 × 10-12 and 0.272 × 10-12 esu respectively. The copolymers exhibit strong reverse saturable absorption and good optical limiting behaviour at 532 nm. © 2008 Elsevier B.V. All rights reserved.Item Design and synthesis of new donor-acceptor type conjugated copolymers derived from thiophenes(2009) Manjunatha, M.G.; Vasudeva Adhikari, A.V.; Hegde, P.K.A new series of donor-acceptor type poly(thiophene) derivatives (P1-P3) were synthesized starting from thiodiglycolic acid and diethyl oxalate through multistep reactions. In the final step, the polymerization was carried out using Wittig reaction. This is a good synthetic route for the preparation of any desired p- and n-type copolymers. The optical and potential charge-transporting properties of the copolymers were investigated by UV-vis, fluorescence emission spectroscopy and cyclic voltammetry. The copolymers exhibited bluish-green/green fluorescence in their thin film forms. Cyclic voltammetry experiments showed that these copolymers have low-lying LUMO energy levels ranging from -2.98 to -3.11 eV and high lying HOMO energy levels ranging from -5.45 to -5.65 eV. The optical and electrochemical studies reveal that new copolymers are new promising materials for the development of efficient polymer light emitting diodes. © 2008 Elsevier Ltd. All rights reserved.Item Synthesis and nonlinear optical characterization of new poly{2,2?-(3,4-didodecyloxythiophene-2,5-diyl)bis[5-(2-thienyl)-1,3,4-oxadiazole]}(2009) Hegde, P.K.; Vasudeva Adhikari, A.V.; Manjunatha, M.G.; Suchand Sandeep, C.S.; Philip, R.A new donor-acceptor type poly{2,2?-(3,4-didodecyloxythiophene-2,5-diyl)bis[5-(2-thienyl)-1,3,4-oxadiazole]} (P) was synthesized starting from thiodiglycolic acid and diethyl oxalate through multistep reactions. The polymerization was carried out using chemical polymerization technique. The optical and charge-transporting property of the copolymer was investigated by UV-vis, fluorescence emission spectroscopic and cyclic voltammetric studies. The copolymer shows UV absorption maxima at 375 nm and displays bluish-green fluorescence in DMF solution. Its electrochemical band gap was determined to be 2.07 eV. The nonlinear optical (NLO) properties of the copolymer was investigated at 532 nm using single beam Z-scan and degenerate four-wave mixing (DFWM) techniques with nanosecond laser pulses. The copolymer exhibits strong optical limiting behavior due to effective three-photon absorption (3PA). Values of the effective 3PA coefficient (?), third-order nonlinear susceptibility (?(3)) and figure of merit (F) have been calculated. © 2009 Elsevier B.V. All rights reserved.Item Ultrafast nonlinear optical properties of dye-doped PMMA discs irradiated by 40 fs laser pulses(2009) Xia, Y.; Jiang, Y.; Fan, R.; Dong, Z.; Zhao, W.; Chen, D.; Umesh, G.The two-photon absorption (TPA) characteristics of PMMA discs doped with three different dyes were studied using an fs-pulsed Ti-Sapphire laser as the pump source, and employing the open-aperture Z-scan technique. TPA cross-sections obtained for PMMA doped with the dyes PM597, DCM and rhodamine 6G-rhodamine B (co-doped) were found to be equal to 24.7, 33.3 and 32.3 GM, respectively (1 GM=10-50 cm4 s phot-1 mol-1). Furthermore, two-photon fluorescence was measured for the samples containing DCM and rhodamine 6G-rhodamine B (co-doped). Compared to the one-photon fluorescence spectrum, the peaks in the two-photon fluorescence spectrum were red shifted and the extent of red shift increased with increasing doping concentration. We have also observed that the red shift in the two-photon fluorescence peak of the samples in the solid form is much larger than that in the solution state. This phenomenon could be explained by a twisted intra-molecular charge transfer model. © 2009 Elsevier Ltd. All rights reserved.Item Optical characterization of a new Donor-acceptor type conjugated polymer derived from 3,4-diphenylthiophene(2009) Manjunatha, M.G.; Vasudeva Adhikari, A.V.; Hegde, P.K.; Suchand Sandeep, C.S.; Philip, R.A new donor-acceptor type poly{2-(3,4-didecyloxythiophen-2-yl)-5-[3,4- diphenyl-5-(1,3,4-oxadiazol-2-yl)thiophen-2-yl]-1,3,4-oxadiazole} (P1) has been designed and synthesized starting from thiodiglycolic acid, 1,2-diphenylethane- 1,2-dione, and diethyl oxalate through multi-step reactions using precursor polyhydrazide route. The charge-transporting and linear optical property of the polymer has been investigated by cyclic voltammetric, UV-visible, and fluorescence emission spectroscopic studies. The UV-visible absorption spectrum of polymer in thin film form showed maxima at 420 nm. The polymer displayed bluish-green fluorescence both in solution and thin film form. The optical band gap is determined to be 2.27 eV. Third-order nonlinear optical property of the new polymer has been investigated at 532 nm using single beam Z-scan and degenerate four wave mixing (DFWM) techniques with nanosecond laser pulses. The absorptive nonlinearity observed for the polymer P1 is of optical limiting type, which arises due to an "effective" three-photon absorption (3PA) process. The third-order nonlinear optical susceptibility (?(3)) of the polymer is found to be 0.831 × 10-12 esu. Both linear and nonlinear optical studies revealed that the new polymer (P1) is a promising material for applications in photonic devices. © 2009 Springer Science+Business Media, LLC.