Three of rhodamine-base fluorescent probes,which were confirmed by ~1HNMR and ~(13)CNMR detection were designed and synthesized. The interactions between Hg~(2+) and probes were investigated via UV absorption spectroscopy and fluorescence spectrum. The results showed that the probe RFS has good selectivity,rapid,sensitive and off-on fluorescence responses to Hg~(2+) in water. After the addition of Hg~(2+) ,the probes solution changed from colorless to red and showed a good linear relationship with Hg~(2+) i...