nan Maria

Theoretical study of the non linear optical properties of alkali metal (Li, Na, K) doped aluminum nitride nanocages

The effect of alkali metal (Li, Na, and K) doping in aluminum nitride (Al12N12) nanocages is studied through density functional theory (DFT) methods. Six new stable compounds of M@Al12N11 and M@Al11N12 are designed theoretically where alkali metal replaces an atom (Al/N) of a nanocage. The stability of the doped nano-cages is evaluated through binding energy calculations. Doping alkali atom M (M = Li, Na, K) into a nanocage significantly reduces the band gap (HOMO–LUMO gap). Polarizability and first hyperpolarizability are calculated using long range separated methods to evaluate the non-linear optical (NLO) properties of these doped systems. The hyperpolarizability of MAl12N11 nanocages is much higher than that of M@Al11N12 nanocages. The higher hyperpolarizability of M@Al12N11 nanocages is believed to arise from participation of excess diffuse electrons, revealed from PDOS.

Mechanistic insight of TiCl4 catalyzed formal [3 + 3] cyclization of 1,3-bis(silyl enol ethers) with 1,3-dielectrophiles

The mechanism of TiCl4 mediated formal [3 + 3] cyclization of 1,3-bis(silyl enol ethers) with 1,3-dielectrophiles is studied at the B3LYP level of density functional theory (DFT) to rationalize the experimental regioselectivity. Methyl and trifluoromethyl substituted 1,3 dielectrophiles are studied theoretically since they show different regioselectivities. Two different mechanisms involving 1,2 and 1,4 addition of 1,3-bis(silyl enol ethers) on 1,3-dielectrophiles are studied for each dienophile. The intramolecular transition metal catalyzed and non-catalyzed dynamic shift of the silyl moiety is also studied. The structure of the 1,3 dienophile and the associated Mulliken charges are the driving forces for different regioselectivities in methyl and trifluoromethyl dienophiles.

Novel quinoxaline based chemosensors with selective dual mode of action: nucleophilic addition and host–guest type complex formation

New quinoxalinium salts 1–5 have been exploited as chemosensors via naked eye, UV-Vis absorption, fluorescence quenching and 1H NMR experiments. New sensors 1–5 showed a dual mode, nucleophilic addition and a host–guest type complex towards anion (F−, AcO− and ascorbate) detection. Small anions (F−/AcO−) showed nucleophilic addition at the C2 position of the quinoxalinium cation, while larger anions (ascorbate), revealed the formation of a host–guest type complex due to the steric hindrance posed by the C3 of the phenyl ring. Nucleophilic addition of small anions (F−/AcO−) leads to the de-aromatization of the quinoxalinium cation. However in the case of the larger anion, ascorbate, the host–guest type complex formation induces changes in the absorption/fluorescence signals of the quinoxalinium moiety. This selective binding has been confirmed on the basis of the 1H NMR spectroscopic technique, whereupon nucleophilic addition of small anions (F−/AcO−) was confirmed by monitoring the characteristic proton NMR signals of Ha and the methylene protons (CH2), which were clearly shifted in the cases of fluoride and acetate ion addition confirming the de-aromatization and nucleophilic addition. Whereas no such peak shifting was observed in the case of ascorbate ion addition confirming the non-covalent addition of ascorbate. Theoretical insight into the selectivity and complexation behavior of the ascorbate ion with the quinoxaline moiety is gained through density functional theory (DFT) calculations. Moreover, the absorption properties of these complexes are modeled theoretically, and compared with the experimental data. In addition, the thermal decomposition of sensors (1 and 2) has been studied by the means of differential scanning calorimetry (DSC), thermogravimetry (TG), and differential thermogravimetry (DTG) to signify their utility at variable temperatures.

Aromaticity of azines through dyotropic double hydrogen transfer reaction

AbstractDensity functional theory calculations have been performed at B3LYP/6–31+G (d) level to quantify the aromaticities of mono- to triazines through dyotropic double hydrogen transfer (DDHT) reaction. The reaction was chosen such that the azines are products of double hydrogen dyotropic rearrangement, and activation barriers and energies of the reactions were functions of the aromaticities of azines. Small activation barriers and high energies of reactions were characteristic of the reactions delivering highly aromatic azines. Synchronicity, reaction energies and energies of activation have been analyzed, and the aromaticity values obtained thereof were compared with the aromaticity values from other geometric and magnetic criteria. Energies of activation were found superior to the energies of reaction for the determination of the aromaticities. Aromaticities of most of the azines were comparable to the aromaticity of benzene. Activation barriers and reaction energies for the dyotropic reactions delivering contiguous or polynitrogeneous azines had thermodynamic contributions arising from the contiguous nature of azines, in addition to the aromaticity related thermodynamic contributions. Moreover, the aromaticity values of azines are also affected by the fusion of azine to the reaction center. When corrected for these factors, the aromaticities of azines using energies of activation for DDHT correlated nicely with the aromaticities of azines reported in the literature through NICS (0) πzz and some other energetic methods. FigureAzines have aromaticities comparable to benzene.

Aromaticities of Five Membered Heterocycles through Dimethyldihydropyrenes Probe by Magnetic and Geometric Criteria

Aromaticities of five membered heterocycles, containing up to three heteroatoms, are quantified through the dimethyldihydropyrene (DHP) probe. Bond fixation caused by the fusion of heterocycles to the dimethyldihydropyrene nucleus (DHPN) was measured by changes in the 1H NMR chemical shifts (magnetic) and bond lengths alterations (structural criterion). Chemical shifts of dihydropyrenes were calculated at GIAO HF/6-31G(d)//B3LYP/6-31