Synthesis of new tripodal receptors—a ‘PET’ based ‘off–on’ recognition of Ag+

A new set of tripodal receptors based upon an aromatic platform have been synthesized in high yields. The compounds have been characterized by spectroscopic techniques and by single crystal X-ray crystallography. These receptors are found to have good extraction ability and high transport rate for Ag(I). The receptor with imine linkages exhibits weak fluorescence emission bands at λmax=413 and 540 nm, upon excitation at λmax=365 nm. The fluorescence spectrum of the receptor shows enhancement in the intensity of the signal at 413 nm on binding with the Ag+ cation. No such significant changes are observed with other metal ions. An absorption at ∼365 nm is typical of an intraligand (π–π∗) transition involving the imine chromophore, which produces a weak emission band at 413 nm due to quenching caused by PET from a neighboring –OH group. Participation of OH group in coordination to the metal ion reduces PET and an enhancement of fluorescence intensity is observed, signaling recognition of the metal ion.