Benzimidazolium-based new simple ratiometric fluorescent sensor for selective detection of dihydrogenphosphate

<div><p>A series of pyridine-coupled benzimidazolium-based receptors <b>1</b>, <b>2</b> and <b>3</b> have been designed and synthesised. In the series, only receptor <b>1</b> is structurally appealing in the selective recognition of H₂PO₄⁻ in CHCl₃ as well as in CH₃CN over a series of other anions. The ratiometric change in emission with a triplet band at 420 nm is the distinctive feature of selective recognition of H₂PO₄⁻ in CHCl₃. In CH₃CN, a ‘turn on’ response is selectively observed. Binding studies have been carried out using fluorescence, UV–vis, ¹H NMR and ³¹P NMR spectroscopic techniques. Experimental results have been correlated with the theoretical findings.</p>