Thermally Activated Delayed Fluorescence-Guided Photodynamic Therapy Through Skeleton-Homologous Nanoparticles: a Rational Material Design for High-Efficient and High-Contrast Theranostics.

Although photoluminescence imaging-guided photodynamic therapy (PDT) is promising for theranostics, it easily suffers from tissue autofluorescence and PDT photoproducts. To develop time-resolved imaging (TRI)-guided PDT with long-lived emission pathways, like thermally activated delayed fluorescence (TADF), is urgent but challenging, because of the triplet competition between radiative transition and reactive oxygen species (ROS) production. Herein, skeleton-homologous nanoparticles are designed and constructed to address this dilemma, thereby achieving in vivo TRI-guided PDT for the first time. This system is formed with a lipophilic TADF core (as a TRI probe) encapsulated by an amphiphilic photosensitizer shell (as the corona exposed to oxygen for PDT), both of which are derived from the same donor-acceptor skeleton to minimize phase separation in the single entity, and enable the same long-wavelength photoexcitation for TRI and PDT. The chloropropylamine group is helpful for endoplasmic reticulum targeting to enhance PDT upon minimizing the ROS transmission path. Synchronously, the TADF core exhibits a delayed fluorescence of 40 µs for a clear TRI. The NPs are eventually applied in vivo with a high signal-to-background ratio (45.25) and outstanding PDT effects in a mouse model of deep-seated kidney cancer. Such a material design is beneficial for developing high-efficient and high-contrast theranostic approaches.