## 4 Conclusions  
In the presented work, a successful synthesis of unsymmetrical iodoquinoline- and benzothiazole-based squaraine dyes bearing amino and methylamino groups is described. All the synthesized dyes displayed narrow and intense absorption bands in the Vis/NIR region regardless of the polarity of the solvent used. Contrary to expectations, the singlet oxygen production quantum yields were similar to those obtained in non-iodinated dyes. Concerning to their photodegradation, the synthesized dyes, except for \(O\)-methylated precursor, showed moderate radiation stability. Interesting results were observed in the Alamar Blue cell proliferation assay in Caco-2 and HepG2 cells. The unsubstituted squaraine dye \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Dye**} & \multirow{2}{*}{**Irradiation Time**} & \multicolumn{2}{c}{**Caco-2**} & \multicolumn{2}{c}{**HepG2**} \\ \cline{3-6}  & & **1 h** & **24 h** & **1 h** & **24 h** \\ \hline \multirow{3}{*}{**10**} & 0\({}^{\prime}\) & \(>\)10 & 8.811 & \(>\)10 & \(>\)10 \\  & 7\({}^{\prime}\) & 2.277 & 2.320 & 9.606 & 5.068 \\  & 14\({}^{\prime}\) & 1.655 & 0.456 & 3.291 & 2.306 \\ \hline \multirow{3}{*}{**12**} & 0\({}^{\prime}\) & \(>\)10 & 4.383 & 4.491 & 2.116 \\  & 7\({}^{\prime}\) & 1.497 & 1.069 & 1.478 & 1.182 \\  & 14\({}^{\prime}\) & 1.322 & 0.989 & 1.145 & 0.903 \\ \hline \multirow{3}{*}{**13**} & 0\({}^{\prime}\) & 9.632 & 3.411 & 2.316 & 1.645 \\  & 7\({}^{\prime}\) & 1.973 & 1.256 & 1.414 & 0.800 \\ \cline{1-1}  & 14\({}^{\prime}\) & 1.567 & 0.751 & 1.441 & 0.732 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Calculated IC\({}_{50}\) values (\(\upmu\)M) for squaraine cyanine dyes **10**, **12** and **13** in Caco-2 and HepG2 cells (95% confidence level) for the different irradiation treatments (0, 7 and 14 min) and irradiated dyes’ incubation times (1 and 24 h). presented relevant in vitro phototherapeutic effects in both cell lines, as it exhibited low antiproliferative effects in the absence of irradiation (IC\({}_{50}\) values higher than or near the maximum tested concentration) and significantly lower half inhibitory concentrations when irradiated. Besides, the introduction of amine groups into the four-membered central ring increased the dark cytotoxicity of the dyes. However, it is noteworthy that the potentiality of these latter dyes is not invalidated since, compared to the dark, the half inhibitory concentration values in the light-presence are distinctly lower. In conclusion, compared to the non-iodinated dyes of our previous study, the inclusion of iodine atoms substantially improved the photobiological performance of these core of unsymmetrical dyes, so these latter bearing this heavy atom have so far intrinsic properties of a PDT photosensitizer candidate. The following are available online at [[http://www.mdpi.com/2076-3417/9/24/5414/s1](http://www.mdpi.com/2076-3417/9/24/5414/s1)]([http://www.mdpi.com/2076-3417/9/24/5414/s1](http://www.mdpi.com/2076-3417/9/24/5414/s1)), Figure S1: \({}^{1}\)H-NMR spectrum of dye **10** (600 MHz, CDCl\({}_{3}\)), Figure S2: \({}^{13}\)C-NMR spectrum of dye **10** (150.9 MHz, CDCl\({}_{3}\)), Figure S3: \({}^{1}\)H-NMR spectrum of dye **11** (600 MHz, CDCl\({}_{3}\)), Figure S4: \({}^{13}\)C-NMR spectrum of dye **11** (150.9 MHz, CDCl\({}_{3}\)), Figure S5: \({}^{1}\)H-NMR spectrum of dye **12** (600 MHz, DMSO-\(d_{6}\)), Figure S6: \({}^{1}\)H-NMR spectrum of dye **12** (600 MHz, DMSO-\(d_{6}\)), Figure S7: \({}^{13}\)C-NMR spectrum of dye **12** (150.9 MHz, DMSO-\(d_{6}\)), Figure S8: \({}^{1}\)H-NMR spectrum of dye **13** (400 MHz, DMSO-\(d_{6}\)), Figure S9: \({}^{1}\)H-NMR spectrum of dye **13** (400 MHz, DMSO-\(d_{6}\)), DMSO-\(d_{6}\)+D\({}_{2}\)O), Figure S10: \({}^{13}\)C-NMR spectrum of dye **13** (150.9 MHz, DMSO-\(d_{6}\)). Conceptualization, L.V.R. and A.M.S. ; Investigation, S.F., E.L., R.E.B., D.F., J.R.F. and L.F.V.F. ; Supervision, L.V.R. and A.M.S. ; Writing-original draft, E.L.; Writing-review & editing, R.E.B., L.F.V.F., A.M.S. and L.V.R.