Santanab Giri

Superhalogens as Building Blocks of Halogen‐Free Electrolytes in Lithium‐Ion Batteries

Most electrolytes currently used in Li-ion batteries contain halogens, which are toxic. In the search for halogen-free electrolytes, we studied the electronic structure of the current electrolytes using first-principles theory. The results showed that all current electrolytes are based on superhalogens, i.e., the vertical electron detachment energies of the moieties that make up the negative ions are larger than those of any halogen atom. Realizing that several superhalogens exist that do not contain a single halogen atom, we studied their potential as effective electrolytes by calculating not only the energy needed to remove a Li(+) ion but also their affinity towards H2O. Several halogen-free electrolytes are identified among which Li(CB11H12) is shown to have the greatest potential.

Super/hyperhalogen aromatic heterocyclic compounds

Aromatic heterocyclic molecules play an important role in synthetic organic chemistry due to their wide range of reactivities. Because of their aromaticity, they have a lower tendency to accept electrons, and have accordingly been found to have very low and even negative electron affinity values. Superhalogens on the other hand mimic the chemistry of halogens by having electron affinity values higher than that of chlorine, which has the highest electron affinity (at 3.6 eV) of the elements in the periodic table. It is therefore challenging to make superhalogens out of aromatic heterocyclic molecules. In the current work, however, we showed that this is indeed possible by carrying out first-principles calculations. By employing a systematic approach, we were able to achieve superhalogenic aromatic heterocycles having an electron affinity value of 6.00 eV.

Investigation of hydrogen induced fluorescence in C60 and its potential use in luminescence down shifting applications

Herein the photophysical properties of hydrogenated fullerenes (fulleranes) synthesized by direct hydrogenation utilizing hydrogen pressure (100 bar) and elevated temperatures (350 °C) are compared to the fulleranes C60H18 and C60H36 synthesized by amine reduction and the Birch reduction, respectively. Through spectroscopic measurements and density functional theory (DFT) calculations of the HOMO-LUMO gaps of C60Hx (0 ≤ x ≤ 60), we show that hydrogenation significantly affects the electronic structure of C60 by decreasing conjugation and increasing sp3 hybridization. This results in a blue shift of the emission maximum as the number of hydrogen atoms attached to C60 increases. Correlations in the emission spectra of C60Hx produced by direct hydrogenation and by chemical methods also support the hypothesis of the formation of C60H18 and C60H36 during direct hydrogenation with emission maxima of 435 and 550 nm respectively. We also demonstrate that photophysical tunability, stability, and solubility of C60Hx in a variety of organic solvents make them easily adaptable for application as luminescent down-shifters in heads-up displays, light-emitting diodes, and luminescent solar concentrators. The utilizization of carbon based materials in these applications can potentially offer advantages over commonly utilized transition metal based quantum dot chromophores. We therefore propose that the controlled modification of C60 provides an excellent platform for evaluating how individual chemical and structural changes affect the photophysical properties of a well-defined carbon nanostructure.

Unusual stability of multiply charged organo-metallic complexes

Stabilization of multiply charged ions in the gas phase has been one of the most fundamental challenges in chemistry since it is hindered either because of fragmentation or auto-electron detachment. Closo-borane B12H122− is among the best known multiply charged di-anion in chemistry where the second electron is bound by 0.9 eV. We show that transition metal based organo-metallic di-anions such as Cr[BC5(CN)6]2 can be even more stable than B12H122− where the second electron is bound by 2.58 eV. This is in contrast to C6H6 which is unstable even as a mono-anion. The unusual stability of the organo-metallic complex is brought about by having the added electrons simultaneously satisfy three separate electron-counting rules, namely the octet rule, the aromaticity rule, and the 18-electron rule. Mono-anionic Mn[BC5(CN)6]2 which is isoelectronic with di-anionic Cr[BC5(CN)6]2 is also found to be very stable. The design of unusually stable singly and multiply charged organo-metallic negative ion complexes in the gas phase opens the door to the synthesis of new salts with potential applications as organic cathodes and electrolytes in Li ion-batteries and beyond. Equally important, electron counting rules can be used effectively to guide the synthesis of electronegative species beyond super- and hyperhalogens, and hence opening the door for new oxidizing agents.

PhSeBr mediated hydroxylative oxidative dearomatization of naphthols – an open air facile one-pot synthesis of ketols

A new methodology for oxidative-dearomatization of planar phenols is described. An economic, viable one-pot metal free protocol for direct conversion of naphthols to α-ketols is reported. Naphthols were found to undergo facile unprecedented oxidative dearomatization with regioselective hydroxylation with phenyl selenyl bromide in open air conditions. Quaternary stereocenters were developed along with formation of sterically demanding α- and γ-ketols with high yields. Functional group tolerance like esters is revealed. A thorough study of the stereoelectronic demands of the unusual oxy-selenium reactive intermediate involved in dearomatization of 1- and 2-naphthols is carried out. 4-Hydroxy cyclohexadieneone and cyclohexadieneone aryl ethers were generated from dialkyl-phenols under similar reaction conditions providing direct evidence of the mechanical postulate. The first instance of the phenoxy–selenium interaction leading to facile dearomatization of arenes is highlighted in this manuscript.

Correction: Triphenylamine-based donor–π–acceptor organic phosphors: synthesis, characterization and theoretical study

Correction for ‘Triphenylamine-based donor–π–acceptor organic phosphors: synthesis, characterization and theoretical study’ by Aravind Babu Kajjam et al., Mater. Chem. Front., 2017, DOI: 10.1039/c6qm00031b.

Atom-Economical Palladium Carbon-Catalyzed de Novo Synthesis of Trisubstituted Nicotinonitriles

A de novo palladium carbon-catalyzed synthesis of trisubstituted nicotinonitriles from easily synthesized homopropagylic or homoallylic aromatic alcohols in the presence of nitriles has been explored. The mechanism proceeds with an interesting generation of a Pd(II)-C palladacycle followed by an oxidative aromatization to generate the pyridine core. The pyridine core is generated with a noteworthy C-C bond cleavage in the case of the substituted nitriles. The moderate yields and easy separation of the products lend a unique importance to this one-pot methodology.

Deltahedral Organo-Zintl Superhalogens

Zintl ions constitute a special type of naked anionic clusters, mainly consisting of Group 13, 14, and 15 elements of the Periodic Table. Due to the presence of multiple negative ions, the chemistry of Zintl ions is unique. They not only form Zintl phases with alkali and alkaline-earth metal cations, but also form organo-Zintl clusters with distinct properties. By first-principles calculations based on density functional theory, we have designed a new deltahedral organo-Zintl cluster with Ge94- as the core and aromatic heterocyclic compounds as ligands. Calculations on such complexes show that they form a special class of system known as a superhalogen (SH), with a high vertical detachment energy of 4.9 eV. The density of states (DOS), partial DOS, and different molecular orbitals give additional information about the bonding features of the complexes.

The Beckmann rearrangement in the framework of reaction electronic flux

Abstract We have computationally investigated the mechanism of Beckmann rearrangement in the framework of reaction electronic flux. The reaction has been studied in three different reaction conditions. The electronic transfer contribution of the reaction electronic flux was found to play a crucial role in this reaction. Natural bond order analysis and dual descriptor provide additional support for elucidating the mechanism of this reaction.

Changes in the photo-absorption spectrum of MEH-PPV in solution

One potential solution to the world’s expanding energy needs is the harnessing of solar energy—an inexhaustible energy source. In part because of the relatively low efficiency, high cost, and short durability of solar cells, only 2% of energy in the US presently comes from solar.[1] Thin film polymer solar cells offer the potential of making solar energy more affordable.[2- 5] However, one of the challenges of polymer solar cells is the limited absorption range. Certain conditions lead to a red shift in absorption offering the possibility of increased light absorption, but the effect is not fully understood. In order to understand what causes a red shift we must study morphology. The morphology of polymer chains refers to their form and structure. Two aspects of morphology are chain conformation and aggregation. Chain conformation refers to the structural arrangement of the chains and aggregation refers to direct mutual attraction of the molecules. The morphology of polymer chains in solution depends on the solvent used and the polymer concentration [6,7] and has a great influence on the conjugation lengths of the chains which in turn has a great influence on absorption. [6,8] Longer conjugation lengths cause the absorption spectrum to red shift. [6,7,9,10] Because of these effects, understanding solvent effects on absorption could make polymer solar cells more efficient. A popular polymer used in solar cells is MEH-PPV [Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4- phenylenevinylene and in particular, the morphology of MEH-PPV chains in solution has a great influence on absorption [6,7,11]. This study will investigate the absorption spectrum of MEH-PPV in solution both experimentally and theoretically.