By introducing a naphthothiadiazole(NT)unit as the main building block,a non-doped and red emissive conjugated polymer poly(9,9-dihexylfluorene-alt-naphthothiadiazole)(PFNT)is readily obtained through a two-step synthesis.Since the NT unit has a large twist angle with its neighboring segment,the aggregation-induced quenching(AIQ)effect of PFNT can be effectively suppressed in the condensed state.As a result,the corresponding PFNT polymer dot(Pdot)exhibits a high fluorescence quantum yield of 53.2%with peak emission at 616 nm,which is one of the most efficient red Pdots known.PFNT Pdot shows good biocompatibility and can be employed for living cell fluorescent imaging with high bright-ness.It also can be used for specific subcellular organelle imaging through immunofluorescence label-ing.Furthermore,the PFNT Pdot demonstrates much better photostability for long-time cell fluorescence imaging than commercial red dyes.The high performances of PFNT Pdot make it a promising fluorescent probe for practical bioapplications.