Fluorescence signaling systems with a cryptand receptor incorporating electron-withdrawing groups: Metal ion specificity and solvent dependence

Fluorescence signaling systems have been synthesized in the format, ‘fluorophore-spacer-receptor’ or ‘receptor-spacer-fluorophore-spacer-receptor’ with a laterally non-symmetric aza cryptand as the receptor and anthracene as the fluorophore. Attachment of electron-withdrawing 2,4-dinitrobenzene or 4-nitrobenzene groups as the side-arms of the cryptand imparts structural rigidity to the cryptand core that leads to selective fluorescence enhancement in presence of a metal ion higher in the Irving–Williams series. The present group of compounds exhibit enhancement selectively in presence of Cu(II) as the input. Additionally, an exciplex emission is also observed due to controlled movement of one of the electron-withdrawing side arms towards anthracene forming π–π stacking interactions. The use of MeCN as the solvent is also crucial as in other solvents no emission takes place.