Heavy‐atom‐free cationic BODIPY dyes designed for singlet oxygen production using low‐energy light

Two new cationic BODIPY dyes have been synthesized and characterized. Methylation of the nitrogen-atoms associated with the isoquino-based BODIPY core provides water solubility via a high-yield one-step process. Dye 2 shows spectroscopic evidence of H-aggregation, while dye 4 incorporates meso-mesityl moieties, preventing aggregation and providing the expected intense absorption slightly shifted to higher energy compared to its neutral precursor BODIPY. Experimental evidence confirms that both dyes are capable of singlet oxygen production. The production of singlet oxygen is modest, with both dyes showing 21% yield as determined by spectroscopic studies with the singlet oxygen quencher DPBF. Photoreactions with plasmid DNA show the ability of these dyes to act as photosensitizers under physiological conditions. Although one of the dyes forms aggregates in solution, this does not appear to hinder its ability to act as a photosensitizer.