Photobleaching of Light-Activated Porphyrin-Functionalized Plastic Coupons for Potential Antimicrobial Applications

Developing greener alternatives for harmful conventional cleaning agents is an important focus for preventing negative impacts on both the environment and human health. One potential alternative of interest is photodynamic inactivation (PDI), where a photosensitizing molecule is used to generate singlet oxygen (¹O₂) and other reactive oxygen species (ROS). ROS, ¹O₂ in particular, are known to react with cellular membranes of bacteria, resulting in cellular death. Porphyrinoids are one of these known light sensitizing species. In this work, zinc(II) 5,10,15,20-tetrakis((N-4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzyl)-4-pyridyl)-21H,23H-porphine tetrabromide is covalently attached to polyethylene terephthalate (PET) via thermal activation of a diazirine to initiate a C-H insertion. With the porphyrin now covalently bonded to the PET, the functionalized PET was assessed at a range of light intensities on its ability to generate ¹O₂ and for antimicrobial activity against Escherichia coli; the results were found to be correlated. Because photobleaching and resultant loss of activity are one of the weaknesses of PDI, the material was further assessed for its ability to withstand various photobleaching conditions. The photobleaching conditions assessed were high intensity light in dry and underwater conditions and ambient light, along with a set of dark controls. Results indicate that after 2 weeks of high intensity irradiation, the material still mediates singlet oxygen generation, albeit less efficiently. This shows promise for the use of this approach as an alternative to conventional cleaning agents.