## 3 Results and Discussion
### Dyes Preparation and Characterization
#### 3.1.2 Betalains from Bougainvillea Bracts
A specific experimental and theoretical study of these betalin pigments, obtained from red beet-roots, can be found in the work by [PERSON] and col. [61]. The absorbed intensity leads to a quantitative estimation of pigment concentration considering the molar absorbance of indicaxanthin and betanin [57; 60]. Applying the formulas in Reference [57] to our experimental results, we find the pigment-relative concentrations listed in Table 3.  
Attending to these values, for purple and pink BG, both pigments corresponding to peaks 1 and 2 are present in the extract in a similar percentage, the relative concentration of indicaxanthin (47.3%) being slightly lower than the betanin concentration (52.7%) for purple BG, and the opposite for pink BG (57.3% indicaxanthin, 42.7% betanin), thus confirming the previous visual inspection. On the other  
Figure 5: Betalains from beetroots: three pigment extracts with solvent solutions 1, 2 and 3. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Peak 1** & **[Betaxanthins]** & **Peak 2** & **[Betanin]** & \(\mathbf{N_{\Phi}}\) \\ \cline{2-7}  & **Abs** & \(\mathbf{\mu M}\) & **(\%)** & **Abs** & \(\mathbf{\mu M}\) & **(\%)** & **(\%)** \\ \hline
**Purple BG** & 0.47 & 7.2 & 47.3 & 0.52 & 8.0 & 52.7 & 34.7 \\
**Pink BG** & 0.88 & 15.2 & 57.3 & 0.74 & 11.4 & 42.7 & 53.2 \\
**Orange BG** & 1.08 & 24.5 & 90.9 & 0.16 & 2.5 & 9.1 & 35.0 \\
**Yellow BG** & 1.21 & 27.9 & 93.8 & 0.12 & 1.8 & 6.2 & 38.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Estimation of concentration (umol) and relative percentage of betaxanthins (absorption Peak 1 at \(\sim\)482 nm) and betanin (Peak 2 at \(\sim\)536 nm) molecules for the four bougainvillea extracts according to Ref. [57]. The last column lists the total number of photons absorbed between 387 and 750 nm by the natural dyes in relative percentages with respect to the absorption of N719 reference dye. hand, for yellow and orange BG dyes, betaxanthins (Peak 1) are present in more than 90%, and betanin is scarce. These relative concentrations may vary with aging or pH, as will be shown later. [PERSON] et al. studied dyes from red bougainvillea as a function of pH [57], and they obtained for water extract (pH 5.7), concentration values of 15.17 uM betaxanthin (57.4%) and 11.26 uM betanin (42.6%), very close to our values for pink BG obtained with water-acetone solvent at similar pH. Figure 3b shows the products of all BG dye spectra and the sun spectrum (the photon flux plotted in Figure 2), giving an idea of the total number of photons which can be converted in electrons by a NDSSC device using these dyes. Comparing with N719, the absorbance of BG dyes is poor at wavelengths above 600 nm, but it is quite good between 400 and 600 nm. The solar spectrum has a maximum of photons at 675 nm and enhances the dye absorbance peaks between 400 and roughly 750 nm. The total number of visible photons (N\({}_{\phi}\)) potentially absorbed for every BG dye can be obtained by integrating Figure 3b curves in the range 387 (TiO\({}_{2}\) limit) to 750 nm. Results for every BG variety are listed in the last column of Table 3 in percentages relative to N \({}_{\phi}\) obtained for N719. According to these values, the pink BG extract is the best bougainvillea dye and purple BG is the less convenient variety for NDSSCs applications, although factors such as the dye absorption onto the TiO\({}_{2}\) semiconductor and dye stability in the device would obviously also determine the final solar cell performance. Comparison of Dye Extracts and Dry Bracts Absorption Spectra  
Before concluding the dye characterization phase for bougainvillea, we have interest in measuring the spectra of dry-colored bracts and comparing them with the corresponding dye solution extract spectra. Regarding the results for dry bracts, reflectance, transmittance and absorption spectra obtained with the spectroradiometer are quite similar for orange and yellow bracts, and on the other hand, for pink and purple as well.