Porphyrin derivatives for photodynamic therapy are frequently modified with hydrophilic groups to improve their water solubility; however, such hydrophilic groups not only improve the solubility but also affect the photodynamic behavior of the compound. The suitable number and pattern of the hydrophilic substituents depend on the nature of the hydrophilic groups. In this article, we explore the optimum architecture for 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TFPP) derivatives bearing 2-hydroxyethylthio substituents. All five derivatives, namely mono-, cis-bis-, trans-bis-, tris- and tetrakis-substituted TFPP, were successfully synthesized by the nucleophilic aromatic substitution of TFPP with 2-hydroxyethanethiol, separated, and subsequently identified using ESI-TOF mass spectrometry and H-1 and F-19 NMR spectroscopies. The hydrophilicity of the compounds increased with an increase in the number of 2-hydroxyethylthio groups. The singlet oxygen and hydroxyl radical generation efficiencies were estimated using chemical probes following photoirradiation (lambda > 500 nm). trans-Bissubstituted TFPP exhibited the highest efficiency for both singlet oxygen and hydroxyl radical generation. The photocytotoxicities of the photosensitizers were evaluated in HeLa cells following photoirradiation (lambda > 500 nm, 16 J cm(-2)), and increased with an increase in number of 2-hydroxyethylthio groups. In the case of 2-hydroxyethylthio-substituted TFPPs, the fully substituted TFPP was the most efficient architecture plausibly because of the result of the hydrophilicity of the compound rather than a greater efficiency in the generation of reactive oxygen species. (C) 2016 Elsevier B.V. All rights reserved.