fluorescence lifetime

fluorescence imaging

imaging-guided photothermal

cell imaging

conjugated polymer

Journal of the American Chemical Society

Semiconducting polymer nanoparticles (SPNs) emitting in the second near-infrared window (NIR-II, 1000-1700 nm) are promising materials for deep-tissue optical imaging in mammals, but the brightness is far from satisfactory. Herein, we developed a molecular design strategy to boost the brightness of NIR-II SPNs: structure planarization and twisting. By integration of the strong absorption coefficient inherited from planar π-conjugated units and high solid-state quantum yield (Φ<sub>PL</sub>) from twisted motifs into one polymer, a rise in brightness was obtained. The resulting pNIR-4 with both twisted and planar structure displayed improved Φ<sub>PL</sub> and absorption when compared to the planar polymer pNIR-1 and the twisted polymer pNIR-2. Given the emission tail extending into the NIR-IIa region (1300-1400 nm) of the pNIR-4 nanoparticles, NIR-IIa fluorescence imaging of blood vessels with enhanced clarity was observed. Moreover, a pH-responsive poly(β-amino ester) made pNIR-4 specifically accumulate at tumor sites, allowing NIR-IIa fluorescence image-guided cancer precision resection. This study provides a molecular design strategy for developing highly bright fluorophores.

Planar and Twisted Molecular Structure Leads to the High Brightness of Semiconducting Polymer Nanoparticles for NIR-IIa Fluorescence Imaging