Photodynamic inactivation (PDI) has been proposed as an alternative therapy to combat bacterial infections. This therapy combines a photosensitizer, visible light, and oxygen to produce reactive oxygen species (ROS), which lead to cell death. In this sense, porphyrins are interesting photodynamic agents, however, they present low absorption in the phototherapeutic window. Therefore, the design of new dyads combining tetrapyrrolic macrocycles and light-harvesting antennas can be useful to increase the absorption in visible region.

In this study, two dyads, P-BDP and ZnP-BDP, were synthesized containing a BODIPY unit linked to a free-base porphyrin and its complex with Zn(II) via a 1,3,5-triazine group. First, an amino-porphyrin was bound to 1,3,5-triazine in 80% yield. In a second step, this structure was reacted with an amino-BODIPY to obtain a dyad (25%). Finally, the third chlorine atom of the triazine unit was substituted by N,N-dimethylethylenediamine in THF (98%). The BODIPY moiety in the dyads acts as a light-harvesting antenna, which produces an intramolecular energy transfer to the porphyrin unit. In addition, the Zn(II) in the tetrapyrrolic macrocycle increases the intersystem crossing, favoring the generation of ROS. In turn, the tertiary amine in the triazine structure can acquire a positive charge at physiological pH by increasing binding to microbial cells. The absorption spectrum of P-BDP and ZnP-BDP resulted in a linear combination of the spectra of the corresponding monomers. The fluorescence spectra showed a strong decrease in the BODIPY emission along with the increase in the porphyrin unit emission, indicating a deactivation (>99%) of the BODIPY singlet state by porphyrin. The photodynamic activity of both dyads is enhanced with respect to that of their porphyrin monomers. Thus, the new dyads present interesting properties to act as phototherapeutic agents.