A Highly Selective Fluorescent Chemosensor for H 2 PO 4 – Based on a Calix[4]arene Tetraamide Derivative

A new neutral fluorescent chemosensor 5 based on a calix[4]arene tetraamide derivative has been synthesized. It exhibits high selectivity for H 2 PO 4 – over a wide range of anions, and the selectivity for H 2 PO 4 – is more than 2700‐fold higher than for F – . In acetonitrile, the fluorescence intensity of 5 is efficiently enhanced about 130 % [( I – I 0 )/ I 0 ] upon the addition of 5 equiv. of H 2 PO 4 – . From the fluorescence titration experiments, the association constant for 5 /H 2 PO 4 – (1:2) was calculated to be 5.48 × 10 9 M –2 . Furthermore, the 1 H NMR spectral and X‐ray crystal studies suggested that multiple hydrogen‐bonding interactions occur between 5 and H 2 PO 4 – .