Selective chromogenic response via regioselective binding of cations: a novel approach in chemosensor design

A calixdiquinone bis-indoaniline derivative with two kinds of potential binding sites, discriminates cations according to their charge/size ratio. Harder and highly oxophilic Eu(III) preferentially interacts with the lower rim quinone oxygens; whereas Na(I) binds to the azacrown moieties. As a consequence of the chromogenic sensorʹs design, these two binding events result in two different responses, Eu(III) causes a remarkable auxochromic change, but Na(I) produces a significant anti-auxochromic effect.