Substituent and Solvent Polarity on the Spectroscopic Properties in Azo Derivatives of 2-Hydroxynaphthalene and Their Difluoroboranes Complexes

Novel fluorescent dyes such as difluoroborane complexes of 1-phenylazonaphthalen-2-ol derivatives were successfully synthesized and characterized with a focus on the influence of a substituent and a solvent on the basic photophysical properties. 1H, 11B, 13C, 15N, and 19F nuclear magnetic resonance (NMR) spectra of substituted 1-phenylazonaphthalen-2-ol difluoroboranes and their parent azo dyes were recorded and discussed. The absorption and emission properties of synthesized compounds were investigated in solvents of varying polarity. They were found to be fluorescent despite the presence of the azo group. The azo group rotation was blocked by complexing with -BF2 to get a red shift in absorption. Solvent-dependent spectral properties of compounds were investigated using Lipper-Mataga and Bakhshiev plot. The calculated DFT energies and Frontier Molecular Orbitals calculations of the studied compounds were proved to be consistent with the experimental observations.

Molecular Interactions and Dielectric Relaxation in the Mixtures of Amines with 2-Fluorobenzoic Acid in 1, 4-Dioxane

For the present study, the estimation of the static dielectric constants (0 ), dielectric constant () at an angular frequency and dielectric loss () of methyl, ethyl and propyl amines with 2-fluorobenzoic acid in 1,4-dioxane were carried using Klystron microwave bench at frequency 9.43GHz. Using the dielectric parameters, the overall relaxation time (1 ) and group rotation relaxation time (2 ) of the polar solute molecules and average relaxation times (0 ) were also determined using Higasi and Gopalakrishna method employing Debye’s equations. The obtained results revealed that, out of five different molar ratios, relaxation time () is maximum at 1:1 molar concentration for all the systems due to inter and intramolecular interactions through hydrogen bonding. In addition, the dipole moment, activation viscous flow (f) and dielectric relaxation (f ) due to molar free energy also been discussed.

The contribution from rotating massive stars to the enrichment in Sr and Ba of the Milky Way

Most neutron capture elements have a double production by r- and s-processes, but the question of production sites is complex and still open. Recent studies show that including stellar rotation can have a deep impact on nucleosynthesis. We studied the evolution of Sr and Ba in the Milky Way. A chemical evolution model was employed to reproduce the Galactic enrichment. We tested two different nucleosynthesis prescriptions for s-process in massive stars, adopted from the Geneva group and the Rome group. Rotation was taken into account, studying the effects of stars without rotation or rotating with different velocities. We also tested different production sites for the r-process: magneto rotational driven supernovae and neutron star mergers. The evolution of the abundances of Sr and Ba is well reproduced. The comparison with the the most recent observations shows that stellar rotation is a good assumption, but excessive velocities result in overproduction of these elements. In particular, the predicted evolution of the [Sr/Ba] ratio at low metallicity does not explain the data at best if rotation is not included. Adopting different rotational velocities for different stellar mass and metallicity better explains the observed trends. Despite the differences between the two sets of adopted stellar models, both show a better agreement with the data assuming an increase of rotational velocity toward low metallicity. Assuming different r-process sources does not alter this conclusion.