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

Phototheranostics with second near-infrared (NIR-II) imaging and photothermal effect have become a burgeoning biotechnology for tumor diagnosis and precise 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 simultaneously enhanced. Herein, a fluorination strategy for designing A-D-A type PTAs with synchronously improved QY and PCE is proposed. Experimental results show that the molar extinction coefficient (epsilon), NIR-II QY, and PCE of all fluorinated PTAs nanoparticles (NPs) are definitely improved compared with the chlorinated counterparts. Theoretical calculation results demonstrate that fluorination can maximize the electrostatic potential difference by virtue of the high electronegativity of fluorine, which may increase intra/intermolecular D-A interactions, tighten molecule packing, and further promote the increase of epsilon, ultimately leading to simultaneously enhanced QY and PCE. In these PTA NPs, FY6-NPs display NIR-II emission extended to 1400 nm with the highest NIR-II QY (4.2%) and PCE (80%). These features make FY6-NPs perform well in high-resolution imaging of vasculature and NIR-II imaging-guided photothermal therapy (PTT) of tumors. This study develops a valuable guideline for constructing NIR-II organic PTAs with high performance.

Automated summary

This study proposes a fluorination strategy for designing phototheranostic agents (PTAs) with improved fluorescence quantum yield (QY) and photothermal conversion efficiency (PCE). The experimental results showed that the fluorinated PTAs nanoparticles (NPs) had increased molar extinction coefficient (epsilon), NIR-II QY, and PCE compared to the chlorinated counterparts. Theoretical calculations suggested that fluorination could maximize the electrostatic potential difference, enhance intra/intermolecular interactions, and tighten molecule packing, leading to the simultaneous enhancement of QY and PCE. The fluorinated PTAs nanoparticles demonstrated high performance in high-resolution imaging and photothermal therapy of tumors. This study provides valuable guidance for constructing high-performance NIR-II organic PTAs.