Synthesis and evaluation of arylfuryl-bis(indolyl)methanes as selective chromogenic and fluorogenic ratiometric receptors for mercury ion in aqueous solution

• Synthesis of novel bis-indolylmethanes functionalized with arylfuran moieties through a straightforward method.
• Selective direct visualization of Hg2+ in aqueous solution.
• Selective fluorescent ratiometric sensing of Hg2+ in aqueous solution.
• Study of the binding process followed by spectroscopic and 1H NMR titrations.

A series of arylfuryl-bis(indolyl)methane derivatives were prepared in good yields by electrophilic substitution of indole with furyl aldehydes through a simple and mild hydrogensulfate-catalysed reaction and studied as chemosensors for transition metal cations by performing spectrophotometric and spectrofluorimetric titrations. Selective recognition of Hg2+ was achieved in organic aqueous mixture (CH3CN/H2O, 7:3) for the various receptors, with an easily detectable colour change from colourless to purple and also through a fluorescence quenching, making these compounds suitable for dual chromo- and fluorogenic ratiometric sensing of Hg2+. The binding stoichiometry between the receptors and Hg2+ was found to be 1:1. The binding process was also followed by 1H NMR titrations which corroborated the previous findings.

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