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

We report herein the synthesis of aza-BODIPY substituted with strongly electron-donating p-(diphenylamino)phenyl substituents (p-Ph N-) at 3,5-positions. The presence of p-Ph N- groups lowers the energy of the singlet excited state (E ) to 1.48 eV and induces NIR absorption with λ at 789 nm in THF. The compound studied is weakly emissive with the emission band (λ ) at 837 nm and with the singlet lifetime (τ ) equal to 100 ps. Nanosecond laser photolysis experiments of the aza-BODIPY in question revealed T →T absorption spanning from ca. 350-550 nm with the triplet lifetime (τ ) 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 ( O ). As estimated by CV/DPV measurements, the p-Ph N- substituted aza-BODIPYs studied exhibits oxidation processes at relatively low oxidation potentials (E ), 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 N- substituted aza-BODIPYs.