An AIE-active fluorophore based dibenzothiophene-S,S-dioxide unit for highly efficient fluorescence imaging and photodynamic therapy†

In this work, we introduced an AIE-active small molecule fluorophore (SOTA) based on electron-withdrawing dibenzothiophene-S,S-dioxide. Thanks to the robust intramolecular charge-transfer characteristic of SOTA with D–A–D architecture, the water-soluble nanoparticles (SOTA NPs) presented impressive two-photon absorption properties and efficient intersystem crossing. A high two-photon absorption cross-section of 7247 GM upon excitation at 700 nm enabled it to be successfully implemented in vascular imaging of in vivo and ex vivo tissues. A moderate penetration depth of 295 μm and an extremely high SNR value of 46 were obtained in two-photon fluorescence imaging for bladder vessels. Moreover, with the aid of the T₂ state, the possibility of intersystem crossing from S₁ to T₁ was further elevated, which was conducive to attaining superior reactive oxygen species (ROS) generation yields. Decent ROS generation capability was confirmed by the attenuated absorption of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) and electron paramagnetic resonance (EPR) experiments for SOTA nanoparticles. A ROS yield of 58.5% was achieved under white light irradiation. The positive photodynamic therapeutic effect on A549 cells has been convincingly demonstrated in vitro. The results indicated that SOTA nanoparticles can be used for two-photon fluorescence imaging and photodynamic therapy.