Fused-Ring Small-Molecule-Based Bathochromic Nano-agents for Tumor NIR-II Fluorescence Imaging-Guided Photothermal/Photodynamic Therapy.

Optical imaging in the second near-infrared (NIR-II) windows reduces much more autofluorescence and photon scattering from biological tissues and allows further tissue penetration depth and superior spatial resolution in living bodies. Herein, a fused-ring 2,2'-((2Z,2'Z)-((12,13-(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2,″3″:4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-]indole-2,10-diyl)bis(methanylylidene))(5,6-difluoro-3-oxo-2,3-dihydro-1-indene-2,1-diylidene))dimalononitrile (TPBT) molecule was explored as a multifunctional tumor theranostic reagent for photothermal/photodynamic therapy guided by NIR-II imaging. The TPBT molecule has an electron-deficient core with a ladder-type multi-fused ring and shows a narrow band gap that can enhance the near-infrared absorption. The -aggregative TPBT NPs were formed by nanoprecipitation with great bathochromic shift in absorption and emission spectra, which endows them with ideal fluorescence imaging ability in the NIR-II region. Moreover, TPBT NPs present both higher photothermal conversion efficiency (∼36.5%) and effective ROS generation ability, making them excellent candidate for cancer photothermal/photodynamic therapy. Moreover, the biocompatible TPBT NPs can effectively passively target tumor sites due to their enhanced permeability and retention effect for more precision treatment. Thus, TPBT NPs as a multifunctional phototheranostic agent in the NIR-II region present promising potential in clinical cancer NIR-II imaging-guided phototherapy.