Showing papers by "Santanab Giri published in 2016"

Organo-Zintl Clusters [P7R4]: A New Class of Superalkalis.

Abstract: Zintl ions composed of Group 13, 14, and 15 elements are multiply charged cluster anions that form the building blocks of the Zintl phase. Superalkalis, on the other hand, are cationic clusters that mimic the chemistry of the alkali atoms. It is, therefore, counterintuitive to expect that Zintl anions can be used as a core to construct superalkalis. In this paper, using density functional theory, we show that this is indeed possible. The results are compared with calculations at the MP2 level of theory. A systematic study of a P73– Zintl core decorated with organic ligands [R = Me, CH2Me, CH(Me)2 and C(Me)3] shows that the ionization energies of some of the P7R4 species are smaller than those of the alkali atoms and hence can be classified as superalkalis. This opens the door to the design and synthesis of a new class of superalkali moieties apart from the traditional ones composed of only inorganic elements.

A Dual‐Characteristic Bidentate Ligand for a Ternary Mononuclear Europium(III) Molecular Complex – Synthesis, Photophysical, Electrochemical, and Theoretical Study

Abstract: The new bipolar ligand 4-{1-(9,9-diethyl-9H-fluoren-2-yl)-1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl}-N,N-diphenylbenzenamine (Phen-Fl-TPA) and its β-diketonate EuIII complex have been designed, synthesized, characterized, and their photophysical and electrochemical properties have been investigated. The UV/Vis absorption and photoluminescence (PL) emission spectra of the Eu complex and Phen-Fl-TPA in solution as well as in the solid state and as thin films were recorded. The PL study indicated that the Eu complex emits narrow-band red emission with an appropriate International Commission on Illumination (CIE) color gamut. Moreover, it also confirmed the efficient energy transfer from the ligand to the Eu3+ ion. Time-dependent DFT (TD-DFT) calculations were performed for the ligand to determine the exact positions of the excited singlet and triplet energy levels. The EuIII complex shows a dominant pathway involving energy transfer between the ligand triplet level and the excited (5D0) level of the EuIII ion. In addition, the theoretically calculated UV/Vis spectrum of the ligand is similar to the experimental one. The Judd–Ofelt theory was applied to the emissive properties of the EuIII complex, and the lifetime was found to be 0.66 ms. The ground-state optimized ligand structure was a good match with the single-crystal structure. The photoluminescence quantum yield (PLQY) of Eu(TTA)3Phen-Fl-TPA (TTA = thenoyltrifluoroacetone) in solution was 34.1 %, and it possess a high thermal decomposition temperature (317 °C), as determined by differential scanning calorimetry/thermogravimetric analysis (DSC-TGA). Electrochemical analysis revealed highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels for the EuIII complex of 5.6 and 2.8 eV, respectively.

Super/hyperhalogen aromatic heterocyclic compounds

Abstract: 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.

Organic heterocyclic molecules become superalkalis.

Abstract: An organic molecule which behaves like a superalkali has been designed from an aromatic heterocyclic molecule, pyrrole. Using first-principles calculation and a systematic two-step approach, we can have superalkali molecules with a low ionization energy, even lower than that of Cs. Couple cluster (CCSD) calculation reveals that a new heterocycle, C3N2(CH3)5 derived from a well-known aromatic heterocycle, pyrrole (C4H5N) has an ionization energy close to 3.0 eV. A molecular dynamics calculation on C3N2(CH3)5 reveals that the structure is dynamically stable.

Synthesis of Diferrocenyl Hydrazone–Enone Receptor Molecules – Electronic Communication, Metal Binding, and DFT Study

Abstract: Synthesis of four new diferrocenyl hydrazone-enone compounds have been carried out by two step reaction process involving 1,1'-diacetylferrocene, hydrazides and ferrocenyl carboxyaldehyde.Structural characterization of two compounds, 6 and 7 by single crystal X-ray diffraction study showed the presence of more stable eclipsed conformation with the two ferrocenyl moieties oriented in trans- geometry.Electrochemical and metal ion sensing properties for the diferrocenyl bifunctionalized compounds have been explored to understand their potential in electronic communication and as receptor molecule.Compounds, 1,1'-[(η5-C5H5)Fe(η5-C5H4)CH═CHC(O)(η5-C5H4)Fe{(η5-C5H4)C(CH3)═N-N(H)C(O)-R}] {R = C6H4-OH (6), C6H4N-p (7) }, showed selective interaction with Pb2+ metal cation and distinct binding interaction with BSA protein.The mode of metal-receptor interaction has been established by DFT studies.The redox properties for the diferrocenyl compounds with variable end groups revealed distinct electronic communication between the two electroactive groups.

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

Abstract: 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.

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

Abstract: 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

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

Abstract: 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.

PhSeBr Mediated Hydroxylative Oxidative Dearomatization of Naphthols — An Open Air Facile One-Pot Synthesis of Ketols.

Abstract: 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.