Although photodynamic therapy (PDT) has thrived as a promising treatment, highly active photosensitizers (PSs) and intense light power can cause treatment overdose. However, extra therapeutic response probes make the monitoring process complicated, ex situ and delayed. Now, this challenge is addressed by a self-reporting cationic PS, named TPE-4EP+, with aggregation-induced emission characteristic. The molecule undergoes mitochondria-to-nucleus translocation during apoptosis induced by PDT, thus enabling the in situ real-time monitoring via fluorescence migration. Moreover, by molecular charge engineering, we prove that the in situ translocation of TPE-4EP+ is mainly attributed to the enhanced interaction with DNA imposed by its multivalent positive charge. The ability of PS to provide PDT with real-time diagnosis help control the treatment dose that can avoid excessive phototoxicity and minimize potential side effect. Future development of new generation of PS is envisioned.