N-amidothiourea based PET chemosensors for anions

Neutral N-amidothiourea based PET anion sensors bearing a pyrene fluorophore, 1-3, were synthesized and their fluorescent response toward anions was assessed. The anion quenching and binding constants were found to be much higher than those of the corresponding PET sensors bearing a simple thiourea receptor despite a higher oxidation potential of the electron donor and a relatively longer spacer (CH2)(3) between the signal reporter and binding receptor in 1-3. This was explained in terms of a much more substantial increase in the electron donating ability of amidothiourea upon anion binding.