Rational Design of Double‐Check Mercury Ion Chemosensors Based on Photochromic Compounds

A new photochromic compound, S1 , containing a trans ‐ cis photoisomerizable unit and a mercury detecting chemosensor unit, has been designed and synthesized. S1 displayed dramatic selectivity for mercury ions over other ions, through fluorescence intensity measurement. In addition, in the photostationary state, a colorimetric response to mercury ions was also achieved. The fluorescence turn‐off of S1 by mercury ions was defined as the first check, while mercury‐induced colorimetric variation in the photostationary state was set as the second check. Thus, a double‐check mercury chemosensor can be achieved.