Rationally designed thiazole-based COF with multiphoton activity for drug delivery and synergistic therapy of deep-seated tumors

Multiphoton absorption photosensitizers (MPAPSs) activated by near-infrared light have attracted considerable attention in the fields of homogeneous photocatalysis, optical imaging, and phototherapy because of their negligible interference, low dilapidation, and deep penetration. Nonetheless, most MPAPSs still face issues such as poor long-range ordering, strong π-π stacking hindrances, and potential metal toxicity. In this study, a rationally designed thiazole-based covalent organic framework (DT-COF) with multiphoton absorption activity was efficiently harvested via one-step preparation from inactive small molecules-namely, dithiooxamide and 1,3,5-triformylbenzene. Theoretical calculation and characterization tests revealed that the good performances of deeper multiphoton-excited fluorescence and photodynamic therapy benefited from the donor-π-acceptor configuration, highly ordered long-range structure, weakened π-π stacking interaction between the layers, and good nonlinear optical properties. Furthermore, tirapazamine (TPZ), a hypoxia-activated chemotherapeutic drug, was encapsulated into DT-COF pores with anastomosing dimensions (drug loading efficiency = 76.2%). The DT-COF targeted the mitochondria and delivered TPZ to the nucleus. Additionally, DT-COF consumed the limited intratumoral oxygen to generate singlet oxygen, which further cooperated with the hypoxic tumor microenvironment to promote the activation of TPZ, thereby achieving synergistic antitumor therapy through the combination of photodynamic therapy and chemotherapy. This study provides a new strategy for the development of MPAPSs and demonstrates their potential in cancer theranostics.