A SOCT-ISC type photosensitizer coumarin-BODIPY promoted by AIE effect: Mechanism of singlet oxygen generation, simulated PDT in A-549 cells and fluorescence imaging in zebrafish

Abstract

A spin−orbit charge-transfer intersystem crossing (SOCT-ISC) type photosensitizer coumarin-BODIPY (CM-BDP) was reported in this paper. Due its aggregation induced emission (AIE) effect, CM-BDP could work under high water content condition. Besides that, another important phenomenon was discovered. In DMSO solvent, the fluorescence emission and the singlet oxygen yield of CM-BDP were almost negligible, while, in 90% water content system, the singlet oxygen yield of CM-BDP was up to 20.9% and a strong TICT fluorescence emission at 648 nm was observed, which indicated the AIE effect could also promote the generation of singlet oxygen by preserving the energy. In terms of the mechanism of generating singlet oxygen, the D-A configuration of CM-BDP could facilitate the process of charge separation, as well as the generation of TICT state. Then, the orthogonal configuration of CM-BDP in TICT state and the small △Est between the TICT state and T2 state could promote the SOCT-ISC process effectively. Combining the femtosecond transient absorption spectra and the DFT theoretical calculations, the photophysical process of CM-BDP was proposed in simplified Jablonski diagram. Moreover, the CM-BDP was also applied to intracellular experiment and zebrafish imaging. In the photo/dark toxicity experiment, cell survival rate of dark toxicity experiment was basically higher than 90%, while its decreased significantly under irradiation. The result of acridine orange/ethidium bromide (AO/EB) stain experiment indicated that the CM-BDP could kill A-549 cancer cells effectively under irradiation and the fluorescence imaging in zebrafish proved that CM-BDP could be further applied in organisms.