Research Article Photodynamic Efficiency of Xanthene Dyes and Their Phototoxicity against a Carcinoma Cell Line: A Computational and Experimental Study Suelen T. G. Buck, 1 Fernanda Bettanin, 2 Ednilson Orestes, 3 Paula Homem-de-Mello, 2 Hidetake Imasato, 1 Rommel B. Viana, 1 Janice R. Perussi, 1 and Albérico B. F. da Silva 1 1 Departamento de Qu´ ımica e F´ ısica Molecular, Instituto de Qu´ ımica de S˜ ao Carlos, Universidade de S˜ ao Paulo, S˜ ao Carlos, SP, Brazil 2 Centro de Ciˆ encias Naturais e Humanas, Universidade Federal do ABC, Santo Andr´ e, SP, Brazil 3 Escola de Engenharia Industrial Metal´ urgica de Volta Redonda, Departamento de Ciˆ encias Exatas, Universidade Federal Fluminense, Volta Redonda, RJ, Brazil Correspondence should be addressed to Paula Homem-de-Mello; paula.mello@ufabc.edu.br, Rommel B. Viana; rommelbv@yahoo.com.br, Janice R. Perussi; janice@iqsc.usp.br, and Alb´ erico B. F. da Silva; alberico@iqsc.usp.br Received 19 August 2016; Accepted 21 November 2016; Published 12 February 2017 Academic Editor: Teodorico C. Ramalho Copyright © 2017 Suelen T. G. Buck et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te aim of this study is to assess the insights of molecular properties of the xanthene dyes [fuorescein (FL), Rose Bengal (RB), erythrosin B (EB), and eosin Y (EY)] to correlate systematically their photodynamic efciency as well as their phototoxicity against a carcinoma cell line. Te phototoxicity was evaluated by comparing the values of the medium inhibitory concentration (IC 50 ) upon HEp-2 cells with the xanthene corresponding photodynamic activity using the uric acid as a chemical dosimeter and their octanol- water partition coefcient (log ). RB was the more cytotoxic dye against HEp-2 cell line and the most efcient photosensitizer in causing photoxidation of uric acid; nevertheless it was the only one characterized as being hydrophobic among the xanthenes studied here. On the other hand, it was observed that the halogen substituents increased the hydrophilicity and photodynamic activity, consistent with the cytotoxic experiments. Furthermore, the reactivity index parameters, electric dipole moment, molecular volume, and the frontier orbitals were also obtained by the Density Functional Teory (DFT). Te lowest dipole moment and highest molecular volume of RB corroborate with its highest hydrophobicity due to heavy atom substituents like halogens, while the halogen substituents did not afect expressively the electronic features at all. 1. Introduction Te photodynamic therapy (PDT) is a promising cancer treatment that involves the systemic or topic administration of a photosensitizer followed by a period of time in which the PS accumulates preferentially in the tumors cells followed by irradiation with visible light of compatible wavelength and absorption of the photosensitizer. Each factor is harmless by itself but when combined with molecular oxygen leads to the generation of lethal cytotoxic species and consequently to cell death and tissue destruction [1–4]. Te photodynamic therapy is an interesting treatment for cancer due to dual selectivity produced by both preferential uptake of the pho- tosensitizer by the diseased tissue and the ability to confne activation of the photosensitizer to this diseased tissue by restricting the illumination to that specifc region. Terefore, PDT allows for the selective destruction of tumors while leaving normal tissue intact [1–5]. Photofrin5, a complex mixture of porphyrin monomers, dimmers, and oligomers, was the frst compound approved by the Food and Drug Administration (FDA) to be used in PDT for the treatment of some types of cancer. Although Hindawi Journal of Chemistry Volume 2017, Article ID 7365263, 9 pages https://doi.org/10.1155/2017/7365263