An asymmetric imidazole derivative as potential fluorescent chemosensor for Fe3+ in aqueous solution

A novel conjugated molecule, L, based on 2,4,5-triphenylimidazole and 6-phenyl-2,2′-bipyridine (HC∧N∧N) was synthesized in two steps. The molecule can recognize Fe3+ in aqueous solution (THF/H2O, 1/1, v/v) by the appearance of new emission bands at 416 and 442 nm, which can be attributed to the emission of the newly formed L-Fe3+ complex. The binding constant of the complex was calculated to be (6.6±0.39)×103 M−1, and its formation was also confirmed by the appearance of isosbestic points at 312 and 381 nm in the UV-visible spectral titration experiment. While other transition and rare-earth metal ions, such as Mn2+, Fe2+, Co2+, Ni2+, Zn2+, Cd2+, Hg2+, Pb2+, Eu3+ and Nd3+, can only cause some decrease of L's fluorescence, alkali and alkaline earth metal ions, such as Li+, Na+, K+, Mg2+ and Ca2+, almost have no effect on L's fluorescence. The fluorescence of L can be recovered by the addition of EDTA to the L-Fe3+ system just due to EDTA's stronger chelating ability than that of L.