A novel boron ketoiminate-based conjugated polymer with large Stokes shift: AIEE feature and cell imaging application

AIE/AIEE-active conjugated polymers have shown great potential in bioimaging applications. However, the absorption of many AIE/AIEE polymers poorly matches with the laser excitation used in confocal imaging, which may greatly affect the imaging quality. In this regard, we designed and synthesized a novel conjugated polymer incorporating π-extended boron ketoiminate units. The resulting polymer shows typical aggregation-induced enhanced emission (AIEE) characteristics and a dominant UV absorption of 447 nm in THF, which matches well with the laser excitation. Moreover, the polymer exhibits a Stokes shift up to 100 nm, which makes it a good candidate for cell imaging applications. The polymer was subsequently encapsulated into amphiphilic poly(styrene-co-maleic anhydride) (PSMA) to yield conjugated polymer nanoparticles (CPNs) (∼65 nm), which can emit bright yellow fluorescence in aqueous media with a quantum yield of 15%. Meanwhile, the HeLa cell imaging results demonstrate that the CPNs exhibit low cytotoxicity and high photostability, which are good contrast agents for biological fluorescence imaging.