Near‐Infrared Photoactive Aza‐BODIPY: Thermally Robust and Photostable Photosensitizer and Efficient Electron Donor

Abstract We report herein the synthesis of aza‐BODIPY substituted with strongly electron‐donating p ‐(diphenylamino)phenyl substituents ( p ‐Ph 2 N−) at 3,5‐positions. The presence of p ‐Ph 2 N− groups lowers the energy of the singlet excited state ( E s ) to 1.48 eV and induces NIR absorption with λ abs at 789 nm in THF. The compound studied is weakly emissive with the emission band ( λ f ) at 837 nm and with the singlet lifetime ( τ S ) equal to 100 ps. Nanosecond laser photolysis experiments of the aza‐BODIPY in question revealed T 1 →T n absorption spanning from ca. 350–550 nm with the triplet lifetime ( τ T ) equal to 21 μs. By introducing a heavy atom (Br) into the structure of the aza‐BODIPY, we managed to turn it into a NIR operating photosensitizer. The photosensitized oxygenation of the model compound–diphenylisobenzofuran (DPBF)‐proceedes via Type I and/or Type III mechanism without formation of singlet oxygen ( 1 O 2 ). As estimated by CV/DPV measurements, the p ‐Ph 2 N− substituted aza‐BODIPYs studied exhibits oxidation processes at relatively low oxidation potentials ( E ox 1 ), pointing to the very good electron‐donating properties of these molecules. Extremely high photostability and thermal robustness up to approximately 300 °C are observed for the p ‐Ph 2 N− substituted aza‐BODIPYs.