Abstract An interesting dimmer (excimer)-induced-AIE characteristic of 2-phenylisothiazolo [5, 4-b] pyridin-3 (2H)-one was observed. By using a ring-opening reaction, we developed a novel fluorescent probe based on sub-micron particles of 2-phenylisothiazolo [5, 4-b] pyridin- 3 (2H)-one in water.