Iodinated BODIPY Compounds: High-Efficiency Photosensitizers for Antimicrobial Photodynamic Therapy Against Agricultural Fungal Diseases

Antimicrobial photodynamic therapy (aPDT) is a promising plant disease control strategy, with low introduction of fungal drug resistance as a key advantage. Photosensitizers (PSs) are pivotal in aPDT, as their performance directly dictates antimicrobial efficacy. This study explored the regulatory effects of halogen atoms (Cl, Br, and I) and the steric hindrance of <i>meso</i>-substituents in BODIPY derivatives on their reactive oxygen species (ROS) production rate and antimicrobial photodynamic activity. Experimental results showed that the inhibition rates of halogenated BODIPY compounds <b>1X</b> (<i>X</i> = Cl, <b>1C</b>; Br, <b>1B</b>, and I, <b>1I</b>) against <i>Valsa mali</i> increased sequentially. Consistently, the EC₅₀ values of compounds <b>1B</b> and <b>1I</b> also decreased in this order, being 0.228 mg/L and 0.114 mg/L respectively, and the ROS production rate exhibited an identical trend. In addition, iodinated BODIPY derivatives with steric hindrance at the 2,6-positions of the <i>meso</i>-aryl group showed superior antimicrobial activity; for example, compounds <b>3I</b>-<b>6I</b> exhibited higher activity than compound <b>7I</b>. Meanwhile, iodinated BODIPYs displayed low toxicity to the nontarget organisms <i>Apis mellifera</i> L. Collectively, iodinated BODIPYs are efficient PSs, holding great application potential in aPDT-mediated plant disease control.