A ferrocene-based organogel with multi-stimuli properties and applications in naked-eye recognition of F− and Al3+

A novel organogelator (F-6) with multiple hydroxyl groups and a ferrocene group was designed and synthesized. F-6/chloroform gel exhibited smart thixotropic property and displayed stimuli responsiveness to temperature, mechanical stress, redox, anions and cations. Further, a gel–sol phase transition was observed when halogen anions (F−, Cl−, Br−) were added. In particular, only the addition of F− converted the color of the gel from orange to red and was therefore unique for F−. More interestingly, Al3+ could also be recognized by the naked eye through the color change and gel–sol transition. The conclusive stoichiometric ratio between F-6 and Al3+ was determined to be 2 : 1. The detection limit of Al3+ by using F-6 for the analysis was calculated to be 6.84 × 10−7 M in CH3OH/H2O (8 : 2, v/v) at room temperature, which is far below the World Health Organization's (WHO) acceptable limit (1.85 μM of Al3+). Thus, the recognition of F− and Al3+ was achieved through the F-6/chloroform gel system, which was uncommon among organogels. It was shown that the ferrocene group played an important role in the response to ions.