BOPHY-Fullerene C₆₀ Dyad as a Photosensitizer for Antimicrobial Photodynamic Therapy

Graphical Abstract

Photosensitizer: The first BOPHY–fullerene C₆₀ dyad (BP-C₆₀) has been synthesized and obtained as two atropisomers. The presence of the BOPHY light-harvesting antenna in the dyad increases the absorption of the fullerene moiety in the visible region and improves its photodynamic action. Photoinduced energy/electron transfer processes (EnT/PeT) take place from BOPHY to fullerene C₆₀. The dyad exhibits an efficient production of reactive oxygen species. BP-C₆₀ is a promising heavy-atom-free photosensitizer with potential application in photodynamic treatments..

Abstract

A novel BOPHY–fullerene C₆₀ dyad (BP-C₆₀) was designed as a heavy-atom-free photosensitizer (PS) with potential uses in photodynamic treatment and reactive oxygen species (ROS)-mediated applications. BP-C₆₀ consists of a BOPHY fluorophore covalently attached to a C₆₀ moiety through a pyrrolidine ring. The BOPHY core works as a visible-light-harvesting antenna, while the fullerene C₆₀ subunit elicits the photodynamic action. This fluorophore–fullerene cycloadduct, obtained by a straightforward synthetic route, was fully characterized and compared with its individual counterparts. The restricted rotation around the single bond connecting the BOPHY and pyrrolidine moieties led to the formation of two atropisomers. Spectroscopic, electrochemical, and computational studies disclose an efficient photoinduced energy/electron transfer process from BOPHY to fullerene C₆₀. Photodynamic studies indicate that BP-C₆₀ produces ROS by both photomechanisms (type I and type II). Moreover, the dyad exhibits higher ROS production efficiency than its individual constitutional components. Preliminary screening of photodynamic inactivation on bacteria models (Staphylococcus aureus and Escherichia coli) demonstrated the ability of this dyad to be used as a heavy-atom-free PS. To the best of our knowledge, this is the first time that not only a BOPHY–fullerene C₆₀ dyad is reported, but also that a BOPHY derivative is applied to photoinactivate microorganisms. This study lays the foundations for the development of new BOPHY-based PSs with plausible applications in the medical field.