Photothermal　therapy　(PTT),　a　powerful　tool　for　non-invasive　cancer　treatment,　has　been　recognized　as　an　alternative　strategy　for　cancer　therapy　in　the　clinic,　and　it　is　promoted　by　optical　absorbing　agents　(photothermal　agents)　that　can　intensively　convert　near-infrared　(NIR)　light　into　thermal　energy　for　cancer　ablation.　Conjugated　polymer　nanoparticles　(CPNs)　have　recently　attracted　extensive　attention　owing　to　their　excellent　photothermal　properties.　However,　the　absorption　of　typical　CPNs　is　mostly　located　in　the　traditional　near-infrared　region　(NIR-I,　700-900　nm),　which　suffers　from　low　tissue　penetration,　so　the　penetration　depth　is　still　limited　and　severely　restricts　their　further　applications.　Compared　with　the　NIR-I　light,　the　second　near-infrared　window　light　(NIR-II,　1000-1700　nm)　could　efficiently　enhance　the　tissue　penetration　depth,　however,　CPNs　which　absorb　NIR-II　region　light　are　still　especially　limited　and　need　further　exploration.　Here,　a　thieno-isoindigo　derivative-based　Donor-Acceptor　(D-A)　polymer　(BTPBFDTS),　which　exhibited　excellent　absorption　characteristics　from　the　NIR-I　to　NIR-II　window,　was　prepared.　After　formation　of　nanoparticles　and　surface　functionalization,　the　prepared　nanoparticles　(NPsBTPBFDTS@HA　NPs)　exhibited　obvious　targeting　ability,　high　photothermal　conversion　efficiency　and　photoacoustic　imaging　effects　under　1064　nm　irradiation.　Both　in　vitro　and　in　vivo　studies　demonstrate　that　our　obtained　NPsBTPBFDTS@HA　nanoparticles　possess　excellent　PTT　efficacy　including　extremely　high　cancer　cell　killing　ability　and　admirable　tumor　elimination　efficiency.　Hence,　this　work　developed　a　promising　photothermal　conversion　agent　based　on　CPNs　for　cancer　ablation.　©　2020　The　Royal　Society　of　Chemistry.