Quinoidal Benzodifurandione-Based Conjugated Polymer as a NIR Photothermal Therapeutic Agent

Conjugated polymers with both strong near-infrared (NIR) absorption coefficients and high photothermal conversion efficiencies represent a class of promising photothermal nanomaterials. However, most donor–acceptor (D-A) type conjugated polymers suffer from relatively weak absorption coefficients. Herein, a conjugated polymer derived from quinoidal benzodifurandione-alt-bithiophene imide (PBFDO-BTI) was synthesized and developed as a novel therapeutic agent for photothermal therapy (PTT). Benefiting from its intrinsic quinoidal structure and acceptor–acceptor (A-A) configuration, PBFDO-BTI exhibits an unexpectedly ultrahigh mass extinction coefficient of 162.9 L g–1 cm–1 at 808 nm. Additionally, transient absorption measurements reveal that the excited-state lifetime of PBFDO-BTI is merely 2.44 ps. Owing to its strong NIR absorption and ultrafast internal conversion process, the water-soluble nanoparticles based on PBFDO-BTI demonstrate excellent photothermal conversion performance, achieving a photothermal conversion efficiency of up to 74.5% at 808 nm. Moreover, these PBFDO-BTI-based water-soluble nanoparticles exhibit remarkable PTT efficacy both in vitro and in vivo.