Comparative study of the effect of photo and photoacoustic stimulation on singlet oxygen production of neutral and water-soluble cationic zinc phthalocyanines

The capacity of a sensitizing molecule to produce singlet oxygen can be measured by determining the singlet oxygen quantum yield of the molecule. This value depends significantly on the method of excitation and the photophysicochemical properties of the molecule. The ability to stimulate a sonophotosensitizing molecule with both sound and light excitation sources can also increase the singlet oxygen production capacity of the molecule. In the present study, we focused on obtaining a sonophotosensitizer with high therapeutic efficacy for sonophotodynamic therapy (SPDT). For this purpose, zinc phthalocyanine bearing pyridine derivative groups (2) and its water-soluble cationic derivative (3) were synthesized, and their singlet oxygen generating capacities were evaluated using both light (photochemical method) and light and sound combination (sonophotochemical method) as excitation sources for phthalocyanines 2 and 3 in DMSO and aqueous solution, respectively. The singlet oxygen quantum yields of the complexes upon photochemical excitation were calculated as 0.79 for 2, 0.68 for 3 in DMSO and 0.31 for 3 in aqueous solution. Sonophotochemical excitation increased the singlet oxygen quantum yields of the complexes by 38% for 2 and 48% for 3, particularly in DMSO. These results revealed that the synthesized sensitizers exhibited exceptional efficiency in the production of singlet oxygen, a critical reactive oxygen species required for efficient cancer cell destruction. These findings provide an important contribution to the development of novel therapeutic agents with light and sound sensitizing properties and suggest that the synthesized complexes can be considered as promising sonophotosensitizer candidates for future studies.