Pyrene excimer-based calix[4]arene FRET chemosensor for mercury(II)

A novel calix[4]arene derivative locked in the 1,3-alternate conformation (2) bearing two pyrene and rhodamine fluorophores was synthesized as a selective sensor for the Hg²⁺ ion. The sensoring is based on FRET from pyrene excimer emissions to ring-opened rhodamine absorption upon complexation of the Hg²⁺ ion. Addition of Hg²⁺ to a mixed solution of 2 gave significantly enhanced fluorescence at ∼576 nm via FRET with excitation at 343 nm. We also found that the pyrene excimer emissions formed by the intramolecular π-π interactions are more effective in obtaining strong FRET bands than those by intermolecular π-π interactions.