Carbon dots for long-term near-infrared afterglow imaging and photodynamic therapy

•CDs derived from chlorine 6 and polyethylene imine were prepared.•CDs could emit NIR phosphorescence with long lifetime over 2 h.•CDs with large tissue penetration (10 mm) and high SNR (98.4).•CDs can be used for deep-tissue and long-term in vivo persistent luminescent imaging.•CDs can produce reactive oxygen species to achieve promoted photodynamic therapy.