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-Ph2N-) at 3,5-positions. The presence of p-Ph2N- groups lowers the energy of the singlet excited state (E-s) to 1.48 eV and induces NIR absorption with lambda(abs) at 789 nm in THF. The compound studied is weakly emissive with the emission band (lambda(f)) at 837 nm and with the singlet lifetime (tau(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 (tau(T)) equal to 21 mu s. 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-1(2)). As estimated by CV/DPV measurements, the p-Ph2N- 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 degrees C are observed for the p-Ph2N- substituted aza-BODIPYs.