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Author

Vijay Kumar

Bio: Vijay Kumar is an academic researcher from Indian Institute of Technology Kanpur. The author has contributed to research in topic(s): Allylic rearrangement & Lewis acids and bases. The author has an hindex of 3, co-authored 3 publication(s) receiving 70 citation(s). Previous affiliations of Vijay Kumar include Indira Gandhi Centre for Atomic Research.

Papers
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Journal ArticleDOI
TL;DR: It is demonstrated that the "green light" emitting fluorenones 7 can be converted to "blue light" emitters 10 by appropriate positioning of donor-acceptor and chromophoric groups onto the fluorene/fluorenone backbone.
Abstract: The “green emission defect” (GED) produced by fluorenones has significantly retarded the commercial scope of fluorene-based B-OLEDs. In this paper, for the first time, it is demonstrated that the “green light” emitting fluorenones 7 can be converted to “blue light” emitting fluorenones 10 by appropriate positioning of donor−acceptor and chromophoric groups onto the fluorene/fluorenone backbone. Additionally, we report an elegant highly rapid synthetic route for donor−acceptor fluorenes and fluorenones at room temperature with excellent yields.

55 citations

Journal ArticleDOI
TL;DR: Key steps of the approach feature expedient, highly regio- and diastereoselective Lewis acid catalyzed Friedel-Crafts reaction of indole with cyclic allylic alcohols and intramolecular reductive Heck reaction.
Abstract: Enantiospecific total syntheses of (+)-hapalindole H and (-)-12-epi-hapalindole U as well as the formal syntheses of (+)-hapalindole Q and (+)-12-epi-fischerindole U isothiocyanate have been described. Key steps of our approach feature expedient, highly regio- and diastereoselective Lewis acid catalyzed Friedel-Crafts reaction of indole with cyclic allylic alcohols and intramolecular reductive Heck reaction. Efficiency of the synthetic route also relies on an alkynyl aluminate complex driven regioselective nucleophilic epoxide opening from a sterically hindered site.

8 citations

Journal ArticleDOI
Abstract: We have studied structural properties of amorphous hydrogenated silicon usingab initio molecular dynamics simulations. A sample was generated by simulated annealing using periodic boundary conditions with a supercell containing 64 silicon and 8 hydrogen atoms. The radial pair distribution functions for Si-Si, Si-H and H-H have been studied at 300 K and are found to be in good agreement with experimental data. Our results show that hydrogen saturates the dangling bonds and reduces bond strain. We also report existence of Si-H-Si bridge sites which are likely to play an important role in understanding the light induced metastability in this material.

7 citations


Cited by
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TL;DR: This review aims to provide an intrinsic link between ketene dithioacetal groups and a variety of other functional groups, which has brought out many new facts that will assist in future designs.
Abstract: Ketene dithioacetals are versatile intermediates in organic synthesis. Extensive research, since the last decade, has given rise to new prospects in their chemistry. The objective of this review is twofold: first, to highlight the new prospects in the chemistry of functionalized ketene dithioacetals, and second, to provide an intrinsic link between ketene dithioacetal groups and a variety of other functional groups, which has brought out many new facts that will assist in future designs.

179 citations

Journal ArticleDOI
TL;DR: A series of fluorene‐based oligomers with novel spiro‐annulated triarylamine structures, namely DFSTPA, TF STPA, and TFSDTC, are synthesized by a Suzuki cross‐coupling reaction, which simultaneously solves the spectral stability problems and hole‐injection and transport issues for fluorenes‐based blue‐light‐emitting materials.
Abstract: A series of fluorene-based oligomers with novel spiro-annulated triarylamine structures, namely DFSTPA, TFSTPA, and TFSDTC, are synthesized by a Suzuki cross-coupling reaction. The spiro-configuration molecular structures lead to very high glass transition temperatures (197–253 °C) and weak intermolecular interactions, and consequently the structures retain good morphological stability and high fluorescence quantum efficiencies(0.69–0.98). This molecular design simultaneously solves the spectral stability problems and hole-injection and transport issues for fluorene-based blue-light-emitting materials. Simple double-layer electroluminescence (EL) devices with a configuration of ITO/TFSTPA (device A) or TFSDTC (device B)/ TPBI/LiF/Al, where TFSTPA and TFSDTC serve as hole-transporting blue-light-emitting materials, show a deep-blue emission with a peak around 432 nm, and CIE coordinates of (0.17, 0.12) for TFSTPA and (0.16, 0.07) for TFSDTC, respectively, which are very close to the National Television System Committee (NTSC) standard for blue (0.15, 0.07). The maximum current efficiency/external quantum efficiencies are 1.63 cd A−1/1.6% for device A and 1.91 cd A−1/2.7% for device B, respectively. In addition, a device with the structure ITO/DFSTPA/Alq3/LiF/Al, where DFSTPA acts as both the hole-injection and -transporting material, is shown to achieve a good performance, with a maximum luminance of 14 047 cd m−2, and a maximum current efficiency of 5.56 cd A−1. These values are significantly higher than those of devices based on commonly usedN,N′-di(1-naphthyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (NPB) as the hole-transporting layer (11 738 cd m−2 and 3.97 cd A−1) under identical device conditions.

145 citations

Journal ArticleDOI
Abstract: The self-assembly of 2,7-bis(10-ethoxycarbonyl-decyloxy)-9-fluorenone (BEF) has been investigated by scanning tunneling microscopy at the liquid/solid interface. The coexistence and reversible tran...

76 citations

Journal ArticleDOI
TL;DR: Through an expedient synthesis, a novel blue emitter, DiSpiroXanthene-IndenoFluorene (DSX-IF) has been designed and synthesized, which possesses good morphological and color stability upon heating, has a high quantum yield, and may be easily polymerized through anodic oxidation.
Abstract: Through an expedient synthesis, a novel blue emitter, DiSpiroXanthene-IndenoFluorene (DSX-IF) has been designed and synthesized. DSX-IF possesses good morphological and color stability upon heating, has a high quantum yield, and may be easily polymerized through anodic oxidation. Small molecule organic light emitting diodes (SMOLEDs), using this promising new dixanthene derivative as a blue emissive layer, exhibit a maximum luminance of ca. 3800 Cd.m−2 with a luminous efficiency of 1 Cd.A−1.

67 citations

Journal ArticleDOI
TL;DR: The incorporation of xanthenyl units into two extended π-conjugated phenylene systems, namely indenofluorene and pentaphenylene, which have been designed and synthesized through short and efficient synthetic approaches.
Abstract: We report herein the incorporation of xanthenyl units into two extended π-conjugated phenylene systems, namely indenofluorene and pentaphenylene. Thus, dispiroxanthene-indenofluorene (DSX-IF) and dispiroxanthene-ladderpentaphenylene (DSX-LPP) have been designed and synthesized through short and efficient synthetic approaches. These two molecules possess a 3π-2-spiro architecture (3π-systems/2-spiro bridges), in which two xanthenyl cores are spirolinked to a π-conjugated backbone either indenofluorene for DSX-IF or pentaphenylene for DSX-LPP. The structural, electrochemical, and photophysical properties of these blue/violet emitters have been studied in detail and compared to those of their 'all carbon' analogues with spirofluorenyl cores instead of spiroxanthenyl cores, namely dispirofluorene-indenofluorene (DSF-IF) and dispirofluorene-ladderpentaphenylene (DSF-LPP), previously reported in the literature. Finally, the application of DSX-IF and DSX-LPP as new light-emitting materials in nondoped organic light emitting diodes is reported. A detailed optical study of the different electroluminescence spectra is notably presented, with an emphasis 1) on the origin of the low-energy emission band observed in the case of DSX-LPP and 2) on the unexpected optical contribution of the well-known hole-transporting-layer NPB (N,N'-di(naphtyl)-N,N'-diphenyl(1,1'-biphenyl)-4,4'-diamine).

64 citations