## 3 Results and Discussion
Furthermore, one should also remember that the Raman spectra of writing inks containing both phthalocyanine dyes and dyes of thetriarylmethane group (typical for type A) will differ significantly at different wavelengths, which is also due to the contribution of resonance effects. As it was mentioned previously, vibrations corresponding to a macrocyclic conjugated \(\pi\)-system, which contains atoms of nitrogen and carbon attributed to a central ring, and vibrations corresponding to fuchsonimine in triarylmethane dyes are the most intense in Raman spectra recorded at 785- and 532-nm excitations, respectively (Figure 5). Figure 3: The structure of a copper phthalocyanine molecule. Figure 4: Raman spectra of writing ink based on triarymethane dyes (B-type). This Raman spectrum was recorded at 532-nm excitation. \begin{table}
\begin{tabular}{c c} \hline
**Common Names (C.I. Generic Name)** & **Structural Formula** \\ \hline Crystal violet & \\ (Basic Violet 3) & \\ \hline Methyl violet & \\ (Basic Violet 1) & \\ \hline OilViolet 5 BN & \\ (Solvent Violet 8) & \\ \hline Acid bright blue & \\ (Acid Blue 1) & \\ \hline Victoria blue B & \\ (Basic blue 26) & \\ \hline \end{tabular}
\end{table} 
Table 3: The structures of some dyes corresponding to B-type writing inks. The results presented above were compared with the Raman peaks of other components of writing inks in order to analyze the overlapping peaks in the Raman spectra. For that purpose, the Raman spectra of pure solvents were measured (Figure 6); as result, the solvent peaks were compared with the peaks of writing ink dyes of different types (Table 5[30; 31; 32]). In Table 4, the frequencies referring to peaks, which were chosen to plot the time dependencies of peak intensity ratios [16], are highlighted in blue. In turn, the peaks marked in bold are the ones that are caused by the presence of solvent in the composition of the writing ink as well as by DMF, which is frequently used for sample preparation. Table 5 shows that many solvent peaks are overlapping, corresponding to writing ink dyes that include those characteristic peaks, which were used for time dependencies [16], i.e., the adequate application of spectral dependencies is only possible after the evaporation of volatile components or their removal by other methods. The previously published results demonstrate such an opportunity [16]. Indeed, as it was shown in [16], the Raman spectrum of writing ink dye is not significantly changed upon heating and subsequent cooling. Taking this into account, the possibility of the removal of volatile components by controlled heating using chromatographic methods was considered. However, this approach \begin{table}
\begin{tabular}{c c c} \hline \multicolumn{2}{c}{**Raman Shift (cm\({}^{-1}\))**} & \\ \hline
**Exp.** & **Lit. Data** & \\ \hline
526 & 524 & \(\delta\)(CNC) \\
563 & 558 & \(\gamma\)(CCC)/\(\delta\)(CNC)/\(\delta\)(CC\({}_{\text{center}}\)C) \\
729 & 724 & \(\gamma\)(CN) \\
765 & 767 & \(\gamma_{\text{s}}\)(CC\({}_{\text{center}}\)C)/\(\gamma_{\text{s}}\)(CN) \\
805 & 805 & \(\delta\)(CH)\({}_{\text{ring}}\) \\
915 & 915 & \(\gamma\)(CC)\({}_{\text{ring}}\) \\
974 & 973 & \(\delta\)(CC\({}_{\text{center}}\)C) \\
1176 & 1178 & \(\gamma_{\text{s}}\)(CC\({}_{\text{center}}\)C)/\(\delta\)(CCC)\({}_{\text{breathing}}\)/\(\delta_{\text{r}}\)(CH\({}_{3}\)) \\
1308 & 1300 & \(\gamma_{\text{ss}}\)(CC\({}_{\text{center}}\)C)/\(\delta\)(CCC)\({}_{\text{ring}}\)/\(\delta\)(CH) \\
1369 & 1369 & \(\gamma\)(CC\({}_{\text{center}}\)C) \\
1448 & 1447 & \(\delta_{\text{ss}}\)(CH\({}_{3}\)) \\
1488 & 1480 & \(\delta_{\text{ss}}\)(CH\({}_{3}\)) \\
1536 & 1536 & \(\gamma\)(C\({}_{\text{ring}}\)N)/\(\delta_{\text{s}}\)(CH\({}_{3}\)) \\
1587 & 1591 & \(\gamma\)(C–C)\({}_{\text{ring}}\) \\
1620 & 1622 & \(\gamma\)(C–C)\({}_{\text{ring}}\) \\ \hline \end{tabular}
\end{table}