Recognition of silver cations by multifarene[2,2] chemosensors with unexpected fluorescence response.

Fluorescent chemosensors based on a new macrocyclic compound, multifarene[2,2], with modification by triazole-linked pyrene or anthracene were synthesized. These macrocyclic sensors exhibited high affinity and selectivity toward Ag over other metal ions, with ratiometric or enhanced response of their fluorescence emissions depending upon the substituent species for coordination to Ag, and an unexpected response to a concentration threshold of the metal cations was discovered. The experimental evidences of fluorescence spectra, H NMR titration, IR spectra, and high-resolution mass spectra suggested the coordination behaviors of the sensors with Ag, that is, the 1:1 complexes were formed with moderate association constants of about 10 L·mol, and the sulfur atoms on macrocyclic ligand should affinite to the metal cations. Energy-minimized structures and frontier orbitals were estimated by quantum chemical calculations with a view to rationalizing the fluorescence response of the multifarene[2,2] sensors upon binding to Ag.