Dual role of silver in a fluorogenic N-squaraine probe based on Ag(I)-π interactions.

In the presence of Ag(i), the monoanion of cyano-N-squaraine (I) generates an intense fluorescence turn-on response. Experimental evidence and DFT calculations reveal a sequence of deprotonation-coordination events in which the Ag(i) ions play a dual role as a Lewis acid and coordinating metal. The observed effect is highly selective for Ag(i) compared to other metals.