Molecular Tweezer based on Zn(salen)-type complexes: role of spacer flexibility on aggregation and sensing properties towards biogenic amines

Biogenic amines (BA) are nitrogen Lewis bases formed by the decarboxylation of amino acids that represent a health hazard when they are formed in foods in inadequate hygienic and storage conditions.1 For the latter reason, the development of chemosensors for the rapid and sensitive detection of BA plays a crucial role in the field of food safety. Recently it was demonstrated that the dinuclear Zn(salen)-type complex 1, having a flexible spacer, is a chromogenic and fluorogenic chemosensor for biogenic amines.2 Considering that spacer flexibility could limit selectivity of the chemosensor,3 here we present the synthesis and characterization of a new dinuclear Zn(salen)-type complex 2, having a rigid spacer, in order to study the role of spacer flexibility on aggregation and sensing properties towards biogenic amines. Through a combinate approach of 1H NMR, 1H DOSY NMR, UV-vis and fluorescence spectroscopy, we have demonstrated that complex 2, forms dimeric aggregates via intermolecular Zn···O interactions in noncoordinating solvents unlike to complex 1 which, under the same conditions, is stable as intramolecular aggregate.4 This different aggregation mode, which could be attributed to rigidity of the spacer, has a significant impact on sensing properties of complex 2. This work was supported by the University of Catania, PIACERI 2020/2022, Linee di Intervento 2 e 3, and partially funded by European Union (NextGeneration EU), through the MUR-PNRR project SAMOTHRACE (ECS00000022).