Fluorination Enhances NIR-Ⅱ Emission and Photothermal Conversion Efficiency of Phototheranostic Agents for Imaging-Guided Cancer Therapy

摘要

Phototheranostics with second near-infrared (NIR-Ⅱ) imaging and photothermaleffect have become a burgeoning biotechnology for tumor diagnosis andprecise treatment. As important parameters of phototheranostic agents (PTAs),fluorescence quantum yield (QY) and photothermal conversion efficiency (PCE)are usually considered as a pair of contradictions that is difficult to be simultaneouslyenhanced. Herein, a fluorination strategy for designing A–D–A typePTAs with synchronously improved QY and PCE is proposed. Experimentalresults show that the molar extinction coefficient (ε), NIR-Ⅱ QY, and PCE of allfluorinated PTAs nanoparticles (NPs) are definitely improved compared withthe chlorinated counterparts. Theoretical calculation results demonstrate thatfluorination can maximize the electrostatic potential difference by virtue ofthe high electronegativity of fluorine, which may increase intra/intermolecularD–A interactions, tighten molecule packing, and further promote the increaseof ε, ultimately leading to simultaneously enhanced QY and PCE. In these PTANPs, FY6-NPs display NIR-Ⅱ emission extended to 1400 nm with the highestNIR-II QY (4.2) and PCE (80). These features make FY6-NPs perform wellin high-resolution imaging of vasculature and NIR-Ⅱ imaging-guided photothermaltherapy (PTT) of tumors. This study develops a valuable guideline forconstructing NIR-Ⅱ organic PTAs with high performance.