Faculty Publications
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Item Synthesis, photophysical and electroluminescence studies of new triphenylamine-phenanthroimidazole based materials for organic light emitting diodes(Elsevier B.V., 2018) Tagare, J.; Ulla, H.; Satyanarayan, M.N.; Sivakumar, S.In this work, two star-shaped small conjugated materials, namely tris(4-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl) amine (PIPTPA) and tris(4-(1-p-tolyl-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)amine (PITTPA) with donor-?-acceptor (D-?-A) structures, were designed and synthesized by combining three phenanthroimidazole arms into an triphenylamine core. A detailed photophysical, thermal, electrochemical and related properties were systematically studied. Furthermore, theoretical calculations (DFT and TD-DFT) were performed to get a better understanding of the electronic structures. Both the materials were found to exhibit high glass transition temperatures (~ 238 °C) and high thermal stabilities with decomposition temperatures up to 298 °C. OLEDs using these materials as emissive materials showed excellent device performance (7.42 cd A?1, 5.77 lm W?1, 4.14% at 100 cd m?2) with green emission and low turn-on voltages. The results demonstrate that TPA integrated with phenthroimdazole plays an important role in the device performance. © 2017 Elsevier B.V.Item Enhancement in fluorescence quantum yield of MEH-PPV:BT blends for polymer light emitting diode applications(Elsevier B.V., 2018) K M, K.M.; Satyanarayan, M.N.; Umesh, G.We have investigated the effect of blending electron deficient heterocycle Benzothiadiazole (BT) on the photo-physical properties of conjugated polymer Poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). Quantum yield (QY) value has been found to increase from 37% for pure MEH-PPV to 45% for an optimum MEH-PPV:BT blend ratio of 1:3. This can be attributed to the efficient energy transfer from the wide bandgap BT (host) to the small bandgap MEH-PPV (guest). The FTIR spectrum of MEH-PPV:BT blended thin film indicates suppression of aromatic C-H out-of-plane and in-plane bending, suggesting planarization of the conjugated polymer chains and, hence, leading to increase in the conjugation length. The increase in conjugation length is also evident from the red-shifted PL spectra of MEH-PPV:BT blended films. Single layer MEH-PPV:BT device shows lower turn-on voltage than single layer MEH-PPV alone device. Further, the effect of electrical conductivity of PEDOT:PSS on the current-voltage characteristics is investigated in the PLED devices with MEH-PPV:BT blend as the active layer. PEDOT:PSS with higher conductivity as HIL reduces the turn on voltage from 4.5 V to 3.9 V and enhances the current density and optical output in the device. © 2018 Elsevier B.V.Item New cyanopyridine based conjugated polymers carrying auxiliary electron donors: From molecular design to blue emissive PLEDs(Elsevier Ltd, 2020) Pilicode, N.; Naik, P.; K M, K.M.; Acharya, M.; Satyanarayan, M.N.; Vasudeva Adhikari, A.V.Three new D-A (Donor-Acceptor) configured conjugated polymers, i.e. PPy1-3, centered on strong electron accepting cyanopyridine scaffold carrying varied auxiliary donors, viz. phenylene (PPy1), biphenyl (PPy2), and fluorene (PPy3) were designed and synthesized as blue emitters for PLEDs. The new polymers were subjected to spectral, thermal, photophysical and electrochemical characterization. Also, computational studies (DFT) were performed on the repeating units of polymer using Turbomole 7.2 V software package at the B3LYP/TZVP hybrid levels. Further, their weight average molecular masses were found to be 38.8 kDa, 38.9 kDa and 57.7 kDa, respectively as determined by GPC technique. Furthermore, the new polymers PPy1-3, were shown to be stable thermally up to 308–374 °C. Evidently, they exhibited good photophysical behavior with their optical energy band gaps of 2.53–2.64 eV. Finally, the polymers PPy1-3 were employed as an active emissive layer in standard ITO/PEDOT:PSS/Polymer/Al configured PLEDs. Interestingly, at 12 V all the newly fabricated devices exhibit a stable blue characteristic electroluminescence with low threshold voltages of 3.40–5.20 V, confirming an efficient injection of electrons in the diodes. From the results, it is clear that, the polymers PPy1-3, can be considered as prospective blue light emitters for PLED application. © 2019 Elsevier LtdItem New cyanopyridine-based ?-conjugative poly(azomethine)s: Synthesis, characterization and electroluminescence studies(John Wiley and Sons Ltd, 2021) Pilicode, N.; Naik, P.; K M, K.M.; Acharya, M.; Satyanarayan, M.N.; Vasudeva Adhikari, A.V.Four new Schiff-base type conjugative polymers (CPs), that is, Py1-4 carrying a strong electron-withdrawing cyanopyridine scaffold coupled with different electron-donating aromatic/heteroaromatic moieties were synthesized from their respective co-monomers by simple poly-condensation route. They were subjected to structural, thermal, photophysical, and electrochemical characterizations and theoretical investigations in order to identify their suitability in polymer light-emitting diode (PLED) application. All these polymers showed good film-forming ability and exhibited favorable photophysical behaviors with an optical bandgap in the order of 2.54-2.68 eV. Further, their electrochemical data were used to evaluate highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels. Finally, Py1-4 were successfully employed as blue-light emitter in the construction of new ITO/PEDOT:PSS/ Py1-4/Al configured light-emitting diodes (LED), and the fabricated devices demonstrated stable blue electroluminescence behavior endorsing an effective electrons injection in the PLEDs. © 2020 John Wiley & Sons Ltd