Calix[4]arene-based, Hg²⁺-induced intramolecular fluorescence resonance energy transfer chemosensor

(Figure Presented) A novel calix[4]arene-based chemosensor 1 based on Hg²⁺-induced fluorescence resonance energy transfer (FRET) was synthesized, and its sensing behavior toward metal ions was investigated by UV/vis and fluorescence spectroscopies. Addition of Hg²⁺ to a CH ₃CN solution of 1 gave a significantly enhanced fluorescence at ∼575 nm via energy transfer (FRET-ON) from the pyrenyl excimer to a ring-opened rhodamine moiety. In contrast, addition of Al³⁺ induced a distinct increase of pyrenyl excimer emission (∼475 nm), while no obvious FRET-ON phenomenon was observed. Different binding behaviors of 1 toward Hg ²⁺ and Al³⁺ were also proposed for the interesting observation.