Browsing by Author "Sivakumar, S."

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Efficient non-doped bluish-green organic light emitting devices based on N1 functionalized star-shaped phenanthroimidazole fluorophores
(Elsevier B.V., 2018) Tagare, J.; Ulla, H.; Satyanarayan, M.N.; Sivakumar, S.
In this paper, two star-shaped fluorescent phenanthroimidazole fluorophores, tris(4-(1-(3-(trifluoromethyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)amine (PIMCFTPA) and tris(4-(1-(4-(trifluoromethyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)amine (PIPCFTPA) with a D–?–A structure were designed and synthesized by attaching a hole-transporting triphenylamine and an electron transporting phenanthroimidazole moiety. A detailed photophysical, thermal, electrochemical and related properties were systematically studied. Furthermore, theoretical investigations (DFT) were performed to get a better understanding of the electronic structures. In particular, PIMCFTPA shows blue shifted emission due to the most twisted conformation and reduced intermolecular interaction as compared with PIPCFTPA. Both the fluorophores exhibit high glass transition temperatures and high thermal stabilities with decomposition temperatures up to 377 °C. The excellent stability renders them promising materials in electroluminescent devices. Non-doped organic light-emitting devices (OLEDs) using these fluorophores as emissive materials display bluish green emissions with high efficiency (6.58 cdA?1, 5.91 lmW?1, 3.62% at 100 cdm?2), low turn-on voltages (2.83 V) (PIMCFTPA) and excellent spectral stability. Our results suggest that the molecular design strategy of integrating TPA with phenthroimdazole play an important role in the device performance. © 2017 Elsevier B.V.
Phenanthroimidazole-based chromophores for organic light-emitting diodes: synthesis, photophysical, and theoretical study
(John Wiley and Sons Ltd, 2020) Tagare, J.; Verma, N.; Tarafder, K.; Sivakumar, S.
Organic light-emitting diodes (OLED) are gaining attention and making a significant contribution to the area of lighting and displays technology. The synthesis of new materials that can act as a host as well as emissive materials is crucial and efforts have been made in this direction in this research. Here, four star-shaped fluorophores, with a donor–acceptor (D–A) structure and with triphenylamine and phenanthroimidazole groups with different substitutions at the N1 position of the imidazole moiety, were designed and synthesized. Synthesized fluorophores showed sufficient thermal stability (10% Td in the range 230–280°C). Ultraviolet–visible (UV–vis) spectra of the fluorophores showed multiple absorption bands (bands in the UV region, due to ?–?* transitions of the conjugated aromatic portion) and all fluorophores showed blue emission in dichloromethane solution. Electrochemical analysis indicated that all fluorophores had excellent oxidation and reduction characteristics. Theoretical calculations were also performed to better understand the structural and electronic properties of the synthesized fluorophores. All fluorophores had higher triplet (T1) energy (ranging from 2.49–2.52 eV) than the widely used green (Ir(ppy)3 –2.4 eV) and red (Ir (piq)2 acac – 2.2 eV) dopant materials. These results indicated that these fluorophores would be useful as host materials for efficient green and red phosphorescent OLEDs. © 2020 John Wiley & Sons, Ltd.
Star-Shaped Phenanthroimidazole-Triphenylamine-Based Yellow Organic Emitter for Organic Light Emitting Diodes
(Wiley-Blackwell, 2017) Tagare, J.; Ulla, H.; Kajjam, A.B.; Satyanarayan, M.N.; Sivakumar, S.
In this work, new star-shaped conjugated organic emitter, namely tris(4-(1-(9,9-diethyl-9H-fluoren-2-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)amine (PIFTPA) with donor-?-acceptor (D-?-A) structure, was designed and synthesized by combining three fluoren-phenanthroimidazole arms into a triphenylamine core and characterized using 1H, 13C NMR and mass spectrometry. The detailed photophysical, thermal, electrochemical and electroluminescence properties were systematically studied. The organic emitter exhibits high glass transition temperature (230 °C) and high thermal stability with decomposition temperature. Electrochemical analysis reveals that the emitter has distinct oxidation and reduction behaviours. Furthermore, theoretical calculations (DFT) were performed to get a better understanding of the electronic structure. The OLEDs using this emitter as emissive material showed good device performance (6.45 cd/A, 4.39 lm/W, and 3.01%) with yellow emission and a low turn-on voltage (2.87 V). The results demonstrate that TPA integrated with phenthroimdazole plays an important role in the device performance. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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.