Large π-extended donor-acceptor polymers for highly efficient in vivo near-infrared photoacoustic imaging and photothermal tumor therapy

Semiconducting polymers(SPs) with intensive near-infrared(NIR) absorption and high photothermal conversion efficiencies have been employed as a new generation of photothermal agents(PTAs) for "all-in-one" theranostic nanoplatforms with integrated photoacoustic imaging(PAI) and photothermal therapy(PTT) functions. However, the lack of facile molecular design principles impedes the development of highly efficient NIR PTAs. Herein, a facile molecular design strategy based on large π-extended donor-acceptor(L-π-D-A) structure is reported for achieving SPs(SP1–SP3) with highly efficient in vitro and in vivo PAI and PTTcapabilities. Through adjusting the conjugation length and planarity of the donor units, both SP3 and corresponding nanoparticle(SPN) SPN3 exhibit stronger D-A strength, intensive NIR absorption, enhanced absorption coefficient, and higher photothermal conversion efficiency(up to 61.8%). The excellent photothermal conversion efficiencies make SPN1–SPN3 produce efficient inhibition of tumor growth with excellent biocompatibility and prominent PAI performance with a high contrast manner in living mice at a low systemic injection mass. Our research highlights that the new L-π-D-A molecular design is an effective strategy to obtain highly efficient polymeric NIR PTAs for high desirable cancer phototheranostic nanoplatforms.