Halogenated BOIMPYs and Their Efficiency in Photodynamic Therapy

BOIMPY (bis- (borondifluoride)-8-imidazodipyrromethene) photosensitizers were developed for imaging-guided photodynamic therapy (PDT). The introduction of heavy atoms (Br and I) to the β-positions of BOIMPY combined with the twisted structure of the molecule was the strategy to enhance the intersystem crossing process of the BOIMPYs and reduce intermolecular π–π interactions of BOIMPY core. To clarify the electronic features of BOIMPY derivatives, their optical properties were studied using UV-vis absorption, fluorescence spectroscopy, electrochemistry, and density functional theory (DFT) computing. The halogenated BOIMPYs exhibited a high absorption coefficient with high singlet oxygen generation ability (Φ_Δ=0.46 and 0.94 for brominated and iodinated BOIMPY, respectively). More significantly, an in vitro investigation showed that all derivatives displayed fluorescence in cancer cells and that the halogenated BOIMPYs increased the effectiveness of tumor inhibition upon exposure to 660 nm red LED light radiation. The half-maximal inhibitory concentrations for the iodinated and brominated BOIMPYs were 2.14 μM and 14.78 μM, respectively. Consequently, iodinated BOIMPY has been shown to represent a new class of photosensitizers with potential use in imaging-guided photodynamic therapy.