A semi-aza-crown-based chemosensor for colorimetric detection of iron(III) and iron(II) in aqueous media with large bathochromic shift

A colorimetric chemosensor, EDDAN (1,1′-((1E,11E)-5,8-dioxa-2,11-diazadodeca-1,11-diene-1,12-diyl)bis(naphthalen-2-ol)), based on a semi-aza-crown structure, was designed and synthesised to sense iron(III) and iron(II). EDDAN showed a unique colour change in the presence of either iron(III) or iron(II), turning from pale yellow to deep purple with large bathochromic shifts. The detection limits of iron(III) and iron(II) were 2.70 and 3.43 μm, respectively. EDDAN displayed a high selectivity for iron ions in the presence of other metal cations except copper(II). In addition, EDDAN showed excellent reversibility by using ethylenediaminetetraacetic acid. Moreover, EDDAN was applied to test strips as well. Based on ultraviolet-visible titrations, Job plots, electron paramagnetic resonance study and electrospray ionisation mass spectrometry analyses, a mechanism for the sensing of iron(III) and iron(II) was also proposed.