**4. DFT calculations, results, and discussion**

In this section, DFT calculation results from our own research are displayed and analyzed. The first set of results contains ground state data, mainly related to energy results including molecular orbitals, energy gap, and relevant chemical properties. In the second set of results are included excited state data with their corresponding molecular orbital diagrams and absorption spectra based on TDDFT calculations.

*Solvents, Ionic Liquids and Solvent Effects*

dihedral values.

C-C bond lengths are in good agreement with our results.

**3. Solvents used to obtain anthocyanidins**

**3.1 Anthocyanidin extraction**

carrying out the extraction procedure.

different solvents resulting in behavior and property changes.

Our results for C-C bonds in average for selected anthocyanidins are within the range of 1.346–1.444 Å with <0.1 Å of difference between the larger and the shorter bonds for all cases. Literature reports for geometries include different methodologies such as B3LYP/6-31G(d) and B3LYP/6-31+G(d,p) [30–33]. All reports are in agreement that B3LYP reaches accurate results for this kind of molecules and overall

Dihedral angles are a good indication of the planarity in a structure; for anthocyanidins, we focused more in analyzing planarity among the three rings that form the molecule skeleton within each anthocyanidin. Also, the literature reports torsion angle as a parameter related to dihedral angles and this value may be used as a factor that helps differentiate anthocyanidins and their electronic structure behavior [30]. Dihedral values show that cyanidin is a planar molecule, selected values are 180°, and in general, all dihedrals are planar or differ with <1°. Peonidin presents more dihedrals that deviate from 180° but only a couple of dihedrals deviate by more than 5°. This last observation occurs for all the selected anthocyanidins; only a couple of dihedrals deviate in a significant amount from planarity but this small difference in the planarity determines the molecule character and its chemical properties. Then, only a few dihedrals indicate a nonplanar structure; these correspond to the relative angle variation observed in the B ring compared with the rest of the structure. These situations occur in all selected structures except in cyanidin which is a planar structure as shown by its

In this section, literature related to the use of solvents during anthocyanidin extraction process is reviewed. Some differences in the material properties depending on the solvents used during its different chemical processes to obtain viable natural dye are expected. The same situation for anthocyanidins prevails, because different processes are used to obtain anthocyanidins in which it is needed to use

Anthocyanidin-rich extracts can be prepared from fresh, frozen, or dried plant materials. Examples of plants rich in anthocyanidins include blueberry [34], elderberry [35], and purple corn [36], among others. The particle size of source materials is an important factor during extraction; milling or grinding procedures among others are used with the goal of increasing surface area as well as the amount of compound obtained from the extraction process. Liquid nitrogen or lyophilization procedures may be complementary options during the grinding step to reduce anthocyanidin degradation. These are important recommendations given that the compounds involved may be subject to degradation caused by various factors, when

A general classification of extraction procedures is based in its phase used during the procedure such as solid or liquid extraction. Solid extraction is applied to liquid matrices, typically only during purification rather than extraction due to saturation of the absorbents. In the case of liquid extraction, a better recovery yield of anthocyanidins may be expected and for this reason, it is the more commonly used technique to extract these pigments from fruit sources. An important note captured from the literature is that there is a general practice that anthocyanidins are extracted with acidified water and polar organic solvents (methanol, ethanol,

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