Intramolecular Charge Transfer of Curcumin and Solvation Dynamics of DMSO Probed by Time-Resolved Raman Spectroscopy

The influence of π-conjugated bridge on photoabsorption and charge transfer characteristics of Diketo-Pyrrolo-Pyrrole derivatives

In this work, three D-π-A-π-D structural Diketo-Pyrrolo-Pyrrole (DPP) derivatives have been designed and simulated, which have the same electron acceptor and donor connected by different π-conjugated bridges. The intramolecular charge transfer (ICT) effects of different electron transport structures on the nonlinear optical response as well as the mechanism have been explored. The results show that a suitable electronic transport structure can enhance the nonlinear optical response of the molecules and expand the absorption spectrum to the long wavelength range, which is of great significance for the practical applications. Impressively, the TDM and CDD maps of molecule constructed with thiophene as π-conjugated bridge exhibit striking excitation response, intense ICT effect as well as a minimal band gap value. The results in this work provide valuable references for the design and synthesis of novel nonlinear optical materials by modifying the electron channel structures.

Aromas: Lovely to Smell and Nice Solvents for Polyphenols? Curcumin Solubilisation Power of Fragrances and Flavours

Natural aromas like cinnamaldehyde are suitable solvents to extract curcuminoids, the active ingredients found in the rhizomes of Curcuma longa L. In a pursuit to find other nature-based solvents, capable of solving curcumin, forty fragrances and flavours were investigated in terms of their solubilisation power. Aroma compounds were selected according to their molecular structure and functional groups. Their capabilities of solving curcumin were examined by UV-Vis spectroscopy and COSMO-RS calculations. The trends of these calculations were in accordance with the experimental solubilisation trend of the solubility screening and a list with the respective curcumin concentrations is given; σ-profiles and Gibbs free energy were considered to further investigate the solubilisation process of curcumin, which was found to be based on hydrogen bonding. High curcumin solubility was achieved in the presence of solvent (mixtures) with high hydrogen-bond-acceptor and low hydrogen-bond-donor abilities, like γ- and δ-lactones. The special case of DMSO was also examined, as the highest curcumin solubility was observed with it. Possible specific interactions of selected aroma compounds (citral and δ-hexalactone) with curcumin were investigated via 1H NMR and NOESY experiments. The tested flavours and fragrances were evaluated regarding their potential as green alternative solvents.

Photoenhancement of the C≡N Stretching Vibration Intensity of Aromatic Nitriles

The C≡N stretching vibration is a versatile infrared (IR) reporter that is useful for a wide range of applications. Aiming to further expand its spectroscopic utility, herein, we show that, using 4-cyanoindole and 4-cyano-7-azaindole as examples, photoexcitation can significantly shift the frequency (ν_CN) and enhance the molar extinction coefficient (ε_CN) of this vibrational mode of aromatic nitriles and that, for these indole derivatives, the enhancement factor can reach 13. Moreover, we find that while solvent relaxation at the excited electronic state(s) always leads to an increase in ε_CN, its effect on ν_CN depends on the solute and the solvent. Taken together, these results demonstrate that solvent relaxation can differently affect the local environment of the nitrile group and its conjugation with the indole ring and, more importantly, that the C≡N stretching vibration can serve as a sensitive IR probe of charge and electron transfer processes in which an aromatic nitrile is involved.