Photostable Rubyrins Bearing Pentafluorophenyl Pendants for Enhanced Reactive Oxygen Species Generation using 808 nm Laser

Abstract

Organic photosensitizers with long-wavelength absorption, photostability and tumour specificity are highly desired in photodynamic therapy (PDT), but the molecular design for this three-in-one formula is quite challenging. Herein, we report the molecular engineering of a series of expanded porphyrinoids with N-anisyl dithienopyrrole (DTP) and meso-pentafluorophenyl substituents to collectively accelerate the reactive oxygen species (ROS) generation. Due to extensive π-conjugation, the Q-bands are significantly red-shifted, reaching into near-IR region and hence, could be photoactivated using the deep-penetrating 808 nm laser. Interestingly, subtle tuning of singlet oxygen production could be achieved by increasing the number of meso-pentafluorophenyl pendants. This was corroborated using photophysical and theoretical studies, which suggested altered electron distribution and stabilization of energy levels for rubyrins with four pentafluorophenyl substituents. On the contrary, the heptaphyrin with increased π-electrons exhibited no ROS generation due to the mismatch in energy gap with molecular oxygen. The photodynamic properties of these macrocycles and their respective nanoparticles confirm them as excellent candidates for PDT due to remarkable ROS generation, exceptional photostability and biocompatibility. The in vitro experiments substantiate the effective anticancer activity of these nanoparticles and offer future scope for in vivo PDT and bioimaging.