Based on Rhodamine,two novel fluorescent Hg2＋ chemosensors（R1,R2） were synthesized from inexpensive starting materials.They were designed and synthesized with o-aminophenol and o-phenylenediamine derivatives as the Hg2＋ chelator,the comparison between the photophysical properties of two chemosensor molecules was made.The chemosensors were designed with a photoinduced electron transfer（PET） mechanism.After binding to Hg2＋ which blocks the PET process,the fluorescence intensity of the chemosensors was enhanced by up to 15-fold.They exhibit very strong fluorescence responses to Hg2＋ and have remarkably higher selectivity for Hg2＋ than for other metal ions including K＋,Na＋,Ca2＋,Mg2＋,Cd2＋,Mn2＋,Ni2＋,Co2＋,Zn2＋,Cu2＋,Cr3＋,Fe3＋,pb2＋,Ag＋,Al3＋,Fe2＋ and Sn2＋ in Tris-HC1/sodium phosphate buffer.The fluorescence enhancement of R2 towards Hg2＋ maintains stable in wide pH span（6.4-8.8） aqueous solutions.
