All-orthogonal BINOLated BODIPY dimers: A synergistic strategy for advancing heavy-metal-free triplet photosensitizers

Covalently linked organic multichromophores are promising photoactive molecular scaffolds for developing valuable heavy-metal-free triplet photosensitizers. Among them, orthogonally connected BODIPY dimers and easily accessible at-boron BINOLated BODIPYs stand out owing to their efficient oxygen photosensitization, without the need for potentially toxic heavy atoms. In both approaches, the key photophysical mechanism enabling triplet state population involves a photoinduced intramolecular charge transfer by symmetry breaking in the orthogonally connected BODIPY dimers, or by electronic push-pull effect in the BINOL-BODIPY dyads. However, the potential synergistic effect of combining both strategies within a single molecular architecture remains unexplored. This work presents the first systematic study on the impact of integrating both photosensitizing approaches within a single BODIPY-based molecular framework. Our findings demonstrate that easy at-boron 3,3′-dibromoBINOLation serves as an effective chemical strategy to enhance triplet-based photosensitizing performance, without relying on potentially toxic heavy atoms such as transition metals. These results are expected to lay the foundations for the rational design of next-generation of low-cost BODIPY-based triplet photosensitizers for applications beyond heavy-metal-free photodynamic therapy, such as photocatalysis.