6,6'-Dibromided tert-butyloxycarbonyl isoindigo (Br-TBOCII) has intense fluorescence in the solid state via excitation with aggregation-induced emission (AIE), contrary to the classic heavy-atom effect. The unique AIE mechanism is attributed to the Br-Br bonding joint restricting intramolecular motion. Furthermore, the water-soluble nanoparticles Br-TBOCII/Pluronic® 127, possess robust photostability, low toxicity and good cell imaging performance.