Design, synthesis, and characterization of pH-responsive near infrared bithiophene Aza-BODIPY

Aza-boron-dipyrromethene (Aza-BODIPY) have been favored by researchers for their excellent performance in photothermal therapy, photodynamic therapy, and bioimaging. In the field of phototherapy, Aza-BODIPY have been pushed forward because of their extensive variety and structural flexibility. Here, two bithiophene Aza-boron-dipyrromethene (Aza-BODIPY) NIR photosensitizers have been successfully synthesized (B5 and B6). Both of the bithiophene Aza-BODIPY exhibit high molar extinction coefficients and are red-shifted in wavelength. The maximum characteristic absorption peak is at 880 nm, and the maximum emission peak is at 880 nm. Bithiophene Aza-boron-dipyrromethene could simultaneously generate heat and singlet oxygen (1O2) under the irradiation of a single laser (808 nm). B5 and B6 each had photothermal conversion efficiencies of 39.84% and 58.14%. At the same time, B5 and B6 have photoacoustic signal generation under laser in the range of 680–900 nm. In addition, the ability of both to produce 1O2 at pH = 5 was significantly enhanced compared to pH = 7. as well as excellent photoacoustic properties. Most significantly, phototoxicity experiments showed that bithiophene Aza-BODIPY (B5) achieved the effect of killing 4T1 tumor cells effect. Finally, to improve the application of Aza-BODIPY, Pluronic F127 was used in self-assembly with the bithiophene Aza-BODIPY.