Fading of a novel colorimetric receptor after recognizing H₂PO₄⁻

A novel selective and sensitive colorimetric receptor 1 (1, 10-phenanthroline-2, 9-dialdehyde bis-(-p-nitrophenylureasemicarbo-hydrazone)) based on urea showing distinctive color fading phenomenon towards H₂PO₄⁻ ion was reported. Fancifully, the recognition process of receptor 1 to H₂PO₄⁻ was not interfered by the existence of others anions. We have probed the binding mechanism of 1-H₂PO₄⁻ that H₂PO₄⁻ ion induced competitive hydrogen binding process via intramolecular hydrogen-bond by UV–vis, fluorescence, ¹H NMR titrations and ESI-MS experiments.