An all-electron acceptor-based semiconducting polymer nanoprobe for in vivo high brightness NIR-II fluorescence imaging

In vivo fluorescence imaging within the second near-infrared window (NIR-II, 1000-1700 nm) has advantages of a higher spatial resolution, and deeper tissue penetration depth than that in traditional near-infrared (NIR-I, 750-950 nm). However, currently reported most of imaging materials showed very low fluorescence quantum yield. Here, we developed a new all-acceptor strategy to design and synthesize a new diketopyrrolopyrrole-based semiconducting polymer nanoparticles (PDP NPs) with high quantum yield ((sic)1.3 % 0.13 %) by Stille reaction of weak and moderate electron acceptor. Such high fluorescence quantum yield may be attributed to the allacceptor strategy effectively reducing the polymeric intrachain charge-transfer effect. The fluorescence quantum yield (0.13 %) of PDP NPs was higher than currently reported most of semiconducting polymer nanoparticles. Thus, the PDP NPs-enhanced NIR-II imaging exhibited clear microvascular networks in living mice as well as xenograft 4T1 tumor with high signal-to-background ratio and spatial resolution. This study not only introduced an all-acceptor strategy to fabricate diketopyrrolopyrrole-based semiconducting polymer nanoparticles, but also provided a convenient and effective approach to amplify the effectiveness of imaging in vivo.