Vijay Kumar

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

Enantiospecific Total Syntheses of (+)‐Hapalindole H and (−)‐12‐epi‐Hapalindole U

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.

Structural properties of amorphous hydrogenated silicon using ab initio molecular dynamics simulations

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.

Recent developments of ketene dithioacetal chemistry.

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.

Multifunctional Fluorene‐Based Oligomers with Novel Spiro‐Annulated Triarylamine: Efficient, Stable Deep‐Blue Electroluminescence, Good Hole Injection, and Transporting Materials with Very High Tg

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.

Two-Dimensional Self-Assembled Molecular Structures Formed by the Competition of van der Waals Forces and Dipole–Dipole Interactions

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...

Incorporation of Spiroxanthene Units in Blue-Emitting Oligophenylene Frameworks: A New Molecular Design for OLED Applications

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).