Abstract
Covalent dimerization and iodine substitution methods were used to synthesize heavy atom free and heavy atom present BODIPY singlet oxygen photosensitizers. Both dimerization and iodization could strongly enhance the excited triplet state (T1) formation up to 95% efficiency. The mechanism for excited triplet state formation was revealed by examining UV–vis electronic absorption, steady state and time resolved visible and NIR luminescence, laser flash photolysis, singlet oxygen chemical trapping, and quantum chemical calculation. The dimerization method shows a different mechanism in T1 generation: photoinduced electron transfer (PET) from lowest lying excited singlet state (S1) followed by charge recombination, instead of the traditional intersystem crossing from S1 state. The PET mechanism makes such a photosensitizer sensitive to solvent polarity. This type of heavy atom free and PET-based photosensitizers could be important in photodynamic therapy of tumor and organic photochemistry.
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