Fluorescent Recognition of Zn by Two Diastereomeric Salicylaldimines: Dramatically Different Responses and Spectroscopic Investigation.

Fluorescence responses of two BINOL-based diastereomeric salicylaldimines toward a variety of metal cations have been studied in methanol solution. It is revealed that both compounds show great fluorescence enhancements in the presence of Zn but not with any other metal ions. Moreover, these two diastereomers exhibit dramatically different responses toward Zn under the same conditions. That is, one can produce much stronger fluorescence enhancement also at a longer wavelength than the other. This fluorescence recognition of Zn also shows distinctive color changes under a UV lamp. Mass and NMR spectroscopic analyses have been used to study the mechanism, which indicates the formation of 2+nZn complexes (n = 2, 3). This work has shed new light on the mechanism of an enantioselective fluorescent recognition of chiral amines promoted by Zn.