New conjugated polymer nanoparticles with high photoluminescence quantum yields for far-red and near infrared fluorescence bioimaging

The development of new aqueous conjugated polymer nanoparticles with high photoluminescence quantum yields (PLQYs) at the far red and near infrared (NIR) spectral regions (>650 nm) as alternative polymer probes for fluorescence imaging is reported. This is achieved through an appropriate chemical design by the introduction of up to four fluorine atoms in the different positions of a donor–acceptor (D–A) polymer backbone consisting of thiophene as the electron donating unit and quinoxaline as the electron withdrawing building block. The resulting series of low synthetic complexity conjugated polymers enable us to perform a detailed structure–properties relationship study between the synthesized conjugated polymers and their corresponding aqueous nanoparticles as prepared by the nanoprecipitation and encapsulation methods. We manage to achieve PLQY for aqueous NIR conjugated polymer probes of 0.1 and a PLQY of 0.18 for the far-red emitting conjugated polymer probes. Furthermore, our work paves the way for the rational design of new conjugated polymers with enhanced PLQY, especially in the NIR spectral region, through better control of the intramolecular and intermolecular polymer chain interactions.