Search

A supramolecular assembly was successfully constructed by 2-amino-5-bromo-3-methylpyridine (ABMP) and 2,4-dihydroxybenzoic acid (DHB) through N+–H⋯O−, N–H⋯O and O–H⋯O hydrogen bonding interactions. The structure of molecular salt was determined by single-crystal X-ray crystallography. Further, the synthesized salt was elucidated by optical, Fourier transform infrared and nuclear magnetic resonance spectroscopic studies. UV–Vis–NIR transmittance spectrum reveals that the ABMP-DHB crystal exhibits a better transmittance in the region of entire visible window, and the lower cut-off wavelength is 358 nm. Thermal property was determined by TG/DTA analysis which indicates that the compound is thermally stable up to 210 °C. The molecular structure of ABMP-DHB crystal was optimized using density functional theory at the B3LYP level with 6-31g(d) basis set. The intermolecular interaction and charge delocalization were theoretically found by natural bond orbital analysis. The existence of various intermolecular contacts was identified through finger plot of Hirshfeld surface analysis. ABMP-DHB shows better scavenging activity against DPPH radical. Fukui functions calculation was applied to find out the reactive site in the crystal. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of naphthalimide Bis-Schiff bases (5a) and (5b) using a dual approach comprising computational and experimental techniques. The synthesized Bis-Schiff base compounds (5) were successfully characterized using UV–visible, fluorescence, Fourier-transform infrared (FT-IR), and 1H nuclear magnetic resonance (NMR) spectroscopies. In ethanol solvent, the experimental absorption peak was observed at 339 nm for compound 5a and at 341 and 433 nm for compound 5b. The computationally calculated absorption peak for compounds 5a was at ~ 343 nm and those for 5b were at 337 and 425 nm. The fluorescence emission bands of compounds 5a and 5b were observed at 383 and 549 nm, respectively, at an excitation wavelength of 338 nm. Additionally, quantum chemical studies of the synthesized compounds were performed to study their molecular structures linear optical and nonlinear optical (NLO) response properties. The molecular geometries were optimized to minimum energy ground state. Compounds 5a and 5b showed third-order NLO polarizability amplitudes of 391.8 × 10–36 and 489.0 × 10–36 esu, respectively, which are significantly larger than those of some standard NLO compounds. The results indicate that the Bis-Schiff base is a promising molecule for use in electronic and optoelectronic devices and biosensors. [ABSTRACT FROM AUTHOR]

The possibility of tuning the chemical structures of oligothiophenes offers various applications in designing of optoelectronics and nonlinear optical (NLO) materials. In the current study, we report a computational study of quinoidal oligothiophenes to explore the influence of type of π-conjugation chains and nature of terminal acceptor groups to push their linear (α) and third-order nonlinear optical (γ) polarizability to a robust limit. The ground-state molecular geometries of designed compounds 1–8 are optimized using DFT at the M06/6-311G** level of theory. Among all the designed compounds, the largest linear isotropic (αiso) and anisotropic (αaniso) polarizability values of 342.7 × 10–36 and 765.6 × 10–36 esu are shown by compound 8 owing to its excellent electronic connection between central thiophene rings and terminal acceptor groups. Similarly, the highest average static third-order nonlinear optical (NLO) polarizability < γ > amplitude of 7448 × 10–36 esu is shown by compound 8 which is ~ 1319, ~ 103, ~ 21, ~ 77, ~ 40, ~ 28, and ~ 13 times greater as compared to compounds 1–7, respectively. Strikingly, comparative analysis of < γ > between compound 8 and p-NA (prototype NLO molecule) reveals that < γ > amplitude of compound 8 is 1021 times more than that of p-NA at the same M06/6-311G** methodology as calculated in current investigation. Remarkably, the large difference between < γ > values of compound 8 and p-NA designates significant potential of our designed compound for various NLO applications. Furthermore, TD-DFT computations indicate that the greater NLO response of compound 8 is because of its higher oscillator strength and lower transition energy in contrast to other designed molecular systems. Moreover, TD-DFT calculations are also used to investigate structure-NLO property relations in terms of frontier molecular orbitals (FMOs), the density of states (DOS), molecular electrostatic potential (MEP), and transition density matrix (TDM) parameters. We believe the current design will instigate the materials science community for such novel motifs with efficient optoelectronic and NLO properties. [ABSTRACT FROM AUTHOR]

In our previous studies, fluorine-substituted carbazoles were synthesized, and these compounds showed promising potential against Gram-positive bacterial stains, including Methicillin-resistant Staphylococcus aureus. However, only three compounds with two F substituents on the 2,4-positions of carbazole showed antibacterial potency against both Gram-positive and Gram-negative bacterial strains. A series of new compounds with two F substituents on the 2,4-positions of carbazole, besides three known ones, were synthesized. The structures were confirmed by infrared spectroscopy, 1H & 13C nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry. Eight compounds showed antibacterial activity. 2,4,6-Trifluoro-9H-carbazole (2), with simple structure, showed potential antibacterial activity against the multidrug resistant NDM-1-producing strains which are not inhibited by commonly used antibiotics. Its water-soluble salt was synthesized but showed less activity. [ABSTRACT FROM AUTHOR]