No abstract

This work presents the determination of acidic strengths at the electronic ground and excited states (pK and ) of three flavonol derivatives using electronic absorption and fluorescence emission spectroscopy. The differences of the pK and values were successfully correlated with the molecular structures according to the substitution pattern at the flavonol structure (hydrogen, diethylamino or fluoro moieties). In order to obtain more information about the observed photoacidity of these superacids, geometry optimizations and excitation energy calculations were performed at the CAM-B3LYP/6-311++G(d,p) level for their neutral, protonated and deprotonated species.

The properties of flexographic inks obtained by the partial replacement of nitrocellulose (NC) resin with different amounts of polyurethane (PU) resins were evaluated for the statistical planning of mixtures to develop an optimum ink formulation. The formulations were developed using a statistical tool and they were found to present properties predicted by the tool. The results indicate that the substitution of the NC resin with PU resins leads to increased resistance of the ink film to delamination. The system obtained with the partial substitution of NC with PU has higher lamination bond strength than the pure NC‐based system. The ink films of the formulations NC‐based and NC/PU‐based were evaluated by spectroscopy UV–vis, both inks have similar transparency of greater than 95% above 575 nm. When exposed to water, milk, and UV light, ink surfaces showed similar behavior in the atomic force microscope, Fourier‐transform infrared spectroscopy, and UV–vis analysis. However, ink formulations with higher PU contents underwent higher photodegradation. Other properties such as the viscosity ink, gloss, coating strength, color, adhesion, and blocking of the NC/PU‐based ink film did not vary significantly when compared to those of the standard ink produced exclusively with NC resin.

This work describes the synthesis of photoactive proton transfer compounds based on the benzazolic core containing the azide group. The compounds present absorption in the UV region and fluorescence emission in the visible region of the spectra with large Stokes shift due to a phototautomerism in the excited state (ESIPT). The azide location on the benzazolic structure presented a noteworthy role on their photophysics, leading to fluorescence quenching. A photophysical study was performed in the presence of NaHS to evaluate their application as an H 2 S sensor. The methodology employed was the reduction of azides to amines using NaHS to mimic H 2 S, resulting in an off−on response fluorescence mechanism. The observed photophysical features were successfully used to explore the azides as fluorescent probes in biological media. In addition, DFT and TD-DFT calculations with the CAM-B3LYP/cc-pVDZ and CAM-B3LYP/jun-cc-pVTZ level, respectively, were performed in order to understand the photophysics features of azide derivatives, where the main interest was to investigate the fluorescence quenching experimentally observed in the azide derivatives.

ESIPT is disfavoured and charge-transfer emission, prior to ESIPT, seems to be responsible for long-emission wavelengths.