## 3 Results and Discussion
### Dyes Preparation and Characterization
#### 3.1.2 Betalains from Bougainvillea Bracts  
The effect of solvent on the extraction of betalains has also been tested in literature [55]. Acetone [56] and acid water [57] have been used as solvents for bougainvillea extracts, although other solvents are possible, i.e., methanol [58] or ethanol [59] solutions, and of course, any of the extracts may undergo further purification [60]. In our group, all the four different solvents listed in Table 1 have been tested in previous works. For instance, the spectra of dye Solutions 1 and 2 are compared with N719 dye spectra in the work by [PERSON] and co-workers [38]. In our work, the best Solution is 1 (acetone/water). This best solvent and the corresponding method have been subsequently applied to four different-colored (yellow, orange, pink, and purple) bougainvillea (BG) bracts. The UV-Vis spectra of the four extracts obtained are compared in Figure 3a, which also includes N719 spectrum for reference. Quantitative data, wavelength and intensity of the main peaks found are listed in Table 2.  
Figure 3: (**a**) UV-Vis spectra of the four bougainvillea extracts obtained. N719 spectrum is also included for comparison. (**b**) Products of all dye spectra in Figure 3a and the sun spectrum (\(\Phi_{\lambda}\)) in Figure 2. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Spectrum (Figure)** & **Peak Type** & \(\lambda\)**(nm)** & **Abs** \\ \hline N719 (3) & Peak 1 & 405 & 1.03 \\  & Peak 2 & 553 & 0.96 \\ \hline Yellow BG (3) & Shoulder 1 & 455 & 1.10 \\  & Peak 1 & 478 & 1.21 \\  & Shoulder 2 & 543 & 0.12 \\ \hline Orange BG (3) & Shoulder 1 & 455 & 1.01 \\  & Peak 1 & 478 & 1.08 \\  & Shoulder 2 & 543 & 0.16 \\ \hline Pink BG (3) & Shoulder 1 & 451 & 0.74 \\  & Peak 1 & 482 & 0.88 \\  & Peak 2 & 535 & 0.74 \\ \hline  & Shoulder 1 & 454 & 0.40 \\ Purple BG (3) & Peak 1 & 484 & 0.47 \\  & Peak 2 & 535 & 0.52 \\ \hline Pink BG tract (4) & Shoulder 1 & 487 & 0.72 \\  & Peak 2 & 547 & 0.79 \\  & Peak 3 & 674 & 0.13 \\ \hline  & Shoulder 1 & 451 & 0.76 \\ Orange BG tract (4) & Peak 1 & 484 & 0.81 \\  & Shoulder 2 & 553 & 0.54 \\  & Peak 3 & 674 & 0.19 \\ \hline Beetroot 1 (5) & Peak 1 & 526 & 0.62 \\ \hline Beetroot 2 (5) & Peak 1 & 519 & 0.24 \\ \hline Beetroot 3 (5) & Peak 1 & 516 & 0.56 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Wavelength and intensity of the main absorbance peaks of the UV-Vis spectra shown in Figures 3–5. Figure 4: Dry bract and dye extract spectra for: (**a**) pink bougainvillea; (**b**) orange bougainvillea. The bougainvillea extracts absorption spectra show two sets of peaks around 480 nm (Peak 1 in Table 2) and 540 nm (Peak 2). These peaks are due to betalain pigments. Betalains can be divided in two groups: (i) betacyanins, red-purple, with light adsorption peaks or bands on 530-540 nm (for example betanidin, which is the smallest betacyanyn with a peak at 542 nm, or betanin with a peak at 535 nm); and (ii) betaxanthins (orange, adsorption on lower wavelengths, for example, indicaxanthin has a peak around 482 nm) [3; 16; 59]. Peak 2 due to betacyanins appears for a wavelength near the maxima of the N-719 dye, which supports the use of these natural dye extracts. Regarding the different bougainvillea varieties, pink and purple spectra are similar, except that for the pink variety, peak 1 is more intense than peak 2, while peak 2 is a bit higher than 1 in purple bougainvillea, which means that the relative concentration of both pigments change in these two varieties. Orange and yellow extracts have almost the same spectral results, with a main peak 1 around 477 nm wavelength, related to indicaxanthin (yellow-orange). The noticeable absence of betanin gives the yellow-orange color to these extracts. These varieties only show a shoulder probably related to betanidin (542 nm). There are scarce publications for orange BG, and some of the published spectra are different to Figure 3a even using acetone as a solvent [56], showing thus the influence not only of the solvent but also of the particular extraction method.