Simple Preparation of Near-infrared-II Organic Small Molecule-based Phototheranostics by Manipulation of the Electron-donating Unit

Organic small molecules hold great promise in the field of phototheranostics by virtue of their clear chemical structure, outstanding biocompatibility, and distinguished repeatability. Whereas the synthetic process of them suffers from multi-step and complex reactions. Meanwhile, most of small molecules employed near-infrared-I (MR-I) fluorescence imaging, which could not effectively provide comprehensive tumor information with high resolution. In addition, the reported small molecules showed unsatisfactory singlet oxygen yield and photothermal conversion efficiency, limiting their extensive application in cancer theranostics. Herein, by conjugating diketopyrrolopyrrole (an electron-withdrawing unit) with benzene, aniline, or 1,2-diaminobenzene (electron-donating units), respectively, three novel small molecules DPP-0, DPP-2 and DPP-4 were designed and synthesized by one-step reaction. DPP-0 NPs, DPP-2 NPs and DPP-4 NPs as phototheranostics were further obtained through nanoprecipitation method by self-assembling with Pluronic F127. It was found that with the increase of amino groups, the absorption/emission peaks of NPs were red-shifted. Especially, DPP-4 NPs exhibited strong absorption in the NW-I region, and the maximum emission peak of DPP-4 NPs was located in the near-infrared-II (MR-II) region, suggesting that the optical properties of small molecules can be regulated by changing the electron-donating unit. After irradiation of DPP-4 NPs with a single laser, excellent MR-II fluorescence signal can be obtained for efficient imaging of tumor with high resolution. Moreover, abundant reactive oxygen species (singlet oxygen yield 34.3%) and hyperthermia (photothermal conversion efficiency 40.2%) can also be produced by irradiation of DPP-4 NPs, realizing the combined photodynamic/photothermal therapy guided by MR-II fluorescence imaging.