A new monostyryl boron dipyrromethene derivative (MS1) appended with two triazole units indicates the presence of Hg2+ among other metal ions with high selectivity by color change and red emission. Upon Hg2+ binding, the absorption band of MS1 is blue-shifted by 29 nm due to the inhibition of the intramolecular charge transfer from the nitrogen to the BODIPY, resulting in a color change from blue to purple. Significant fluorescence enhancement is observed with MS1 in the presence of Hg 2+; the metal ions Ag+, Ca2+, Cd2+, Co2+, Cu2+, Fe2+, Fe3+, K +, Mg2+, Mn2+, Ni2+, Pb 2+, and Zn2+ cause only minor changes in the fluorescence of the system. The apparent association constant (Ka) of Hg 2+ binding in MS1 is found to be 1.864 × 105 M -1. In addition, fluorescence microscopy experiments show that MS1 can be used as a fluorescent probe for detecting Hg2+ in living cells.