A colorimetric Ag+ chemosensor based on a cyclometalated ruthenium complex with deprotonated 2-phenylbenzimidazole

A cyclometalated ruthenium complex ( 1 ) using 2-phenylbenzimidazole as a C,N-ligand was developed as a colorimetric chemosensor to detect Ag + ions. Upon the addition of Ag + ions, the absorption spectra of complex 1 demonstrated no change in CH 3 CN solution. However, an excellent solution color change from dark-green to purple and absorption spectral change with a blue-shift of 27 nm (from 612 to 585 nm) were clearly observed after Ag + ions were added to the solution of 1 with 2-fold of fluoride (denoted as 1  + F − ). When Ag + ions were replaced by other common metal ions, the solution color changed from green to red. Therefore, the solution of 1  + F − can be used to distinguish Ag + from the other common metal ions. The absorption intensity at 612 nm exhibited a good linear correlation for the detection of Ag + ion from 0 to 4 µM with a detection limit of 0.34 µM. According to the absorption and 1 HNMR spectral changes of complex 1 , the reaction mechanism is proposed to be as a coordination between silver ion and the deprotonated nitrogen in imidazole. However, the interactions of other metal ions with 1  + F − are related to a proton transfer process.