## 3 Results and Discussion
### UV-Visible (UV-Vis) Spectroscopy  
UV-Vis spectroscopy was used as a complementary tool for further study of dyes present in the solvated ink samples, particularly crystal violet dye. The presence of some other dyes was identified whenever possible based on similar studies in the literature. The concentration of crystal violet in the studied samples was also investigated using absorbance measurements. A \(10^{-5}\) M solution of crystal violet dye dissolved in ethanol was used as a standard. Figure S2 displays the absorption spectrum of the ethanolic solution of crystal violet, which features two bands, a \"B\" band in the UV region at 303 nm, and a \"Q\" band in the visible region at 582 nm. Figure 10 displays the UV-Vis spectra of the 20 ppm solutions of the 12 selected solvated ink samples of subgroups I-IV. The UV-Vis absorption spectra of the solvated ink samples of subgroup I (Figure 10a) are characterized by absorption peaks typical of crystal violet. Similarly, the remaining solvated ink samples of subgroups II-IV also expressed the two featured absorption peaks of crystal violet as can be seen in Figure 10b,d. The concentration and ratio of the crystal violet in the different ink matrices of the samples of subgroups I-IV were calculated using the Beer-Lambert law (\(A=\varepsilon\ell\)), where A is absorbance (582 nm), \(\varepsilon\) is molar absorption coefficient, and \(\ell\) is optical path length (1 cm). The calculated concentrations and ratios of the crystal violet in the different samples are listed in Table S2. The ratio of crystal violet percent in the different solvated ink matrices varied from the minimum 6.36% in PE1 to 35.9% in PK1. Interestingly, the absorption spectrum of the solvated ink sample of VN1 from subgroup II (Figure 10b) featured a shoulder absorption at 617 nm which could be related to the D5 dye. Moreover, the UV-Vis spectra of the solvated ink samples of subgroup IV (Figure 10d) demonstrated distinctive characteristics, as indicated by the presence of additional B and Q bands in the UV and visible regions centered around 343 nm around 667 nm, respectively, as can be seen in Figure 10d. These distinct absorption features could suggest the presence of a phthalocyanine dye, which is a common colorant in the matrices of the BP ink formula [22; 23]. The chemical structure of a typical phthalocyanine dye is shown in Figure S3. The low relative absorption observed in the case of ZR1a and TO3 samples could be attributed to their limited solubility in ethanol, which further suggests the existence of phthalocyanine dyes (Figure S3) with low solubility [25; 33]. Figure 10: UV–Vis spectra of solutions of the solvated ink samples of (**a**) subgroup I, (**b**) subgroup II, (**c**) subgroup III, and (**d**) subgroup IV. To further investigate the contribution of the different dyes besides the crystal violet to the absorption spectral characteristics of solvated inks, curves of selected UV-Vis spectra were fitted, and absorption maxima other than those of crystal violet were determined. Figure S4 displays the deconvoluted UV-Vis absorption spectra of the RX1 and RE1a samples of subgroups I and II, respectively. The deconvoluted absorption spectrum of the RX1 sample suggests the presence of a convoluted peak at 536 nm, which could be related to the D1 dye. Additionally, the deconvoluted absorption spectrum of the RE1a sample shows a secondary absorption peak centered around 530 nm, which could be related to the D2 dye. The above TLC and UV-Vis results (Figure 7, Figure 10 and Figure S4) indicate the presence of dye components other than crystal violet as indicated by the broad absorption spectral profiles and the additional peaks obtained upon spectral deconvolution. The absorption maxima of the other dyes indicated by the UV-Vis spectra and deconvoluted data (Figure 10 and Figure S4) suggest that the (D1-D3) dyes (Figure 7) could belong to the triarylmethane family, which typically expresses absorption features overlapping with crystal violet.