Fluorescent Recognition of Zn2+ 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 2+ but not with any other metal ions. Moreover, these two diastereomers exhibit dramatically different responses toward Zn 2+ 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 2+ 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+ n Zn 2+ complexes ( n = 2, 3). This work has shed new light on the mechanism of an enantioselective fluorescent recognition of chiral amines promoted by Zn 2+ .