Harnessing Photoexcited-State Pathways in Boron Dipyrromethene for Phototheranostics and Photopolymerization.

Boron dipyrromethene (BODIPY) dyes are widely recognized for their strong visible-light absorption, high fluorescence, and structural modularity. Beyond fluorescence, molecular engineering can redirect their photoexcited states toward distinct photochemical pathways, expanding their utility in photomedicine and materials chemistry. This Spotlight examines BODIPY photochemistry from this excited-state perspective and connects recent advances in phototheranostics and photopolymerization. In phototherapy, BODIPY excited states can be directed toward triplet-state energy transfer for singlet-oxygen generation, photoinduced electron transfer to form radicals and biomolecular redox modulation, or nonradiative relaxation for photothermal and photoacoustic applications. The same photochemical principles extend to polymer synthesis, where electron transfer with co-initiators or direct photoinduced bond cleavage supports visible-light photoredox catalysis, photobase generation, and Type I photoinitiation. These pathways have been used in applications ranging from panchromatic photocuring to hydrogel formation, holographic patterning, and 3D printing. Overall, BODIPYs provide programmable photoactive platforms whose functions depend on how molecular structure and the local environment distribute excitation energy among competing pathways. Across these applications, excited-state energies, redox properties, and bond dissociation energies provide complementary parameters for directing BODIPY photochemistry. Emerging quantitative structure-property relationship (QSPR) and machine-learning approaches may further complement these mechanistic design principles by enabling prediction of BODIPY photophysical and photosensitization behavior from molecular structure.