Interestingly, 16 and 17 had a very good phototoxic effect on the colon carcinoma cell line (Fig. and), whilst they were the most difficult to handle during the photophysical characterization studies. Their non-emissive singlet state properties led to an efficient triplet excited state formation and a low singlet oxygen generation (ΦΔ = 0.10 in ethanol), yet suitable to develop the desired phototoxic effect. It seems that the polar hydroxyl and carboxyl groups can enhance the phototoxicity effect since the post-functionalized 17 exhibits greater phototoxicity in comparison with its precursor 13d. The IC50 values of 16 and 17 are low with 1.8 μM and 3.5, respectively.