Fluorescent change of pyreneamide bearing calix[4]crown-5: INHIBIT logic gate in K+-induced H2PO4- complexation

The fluorescence excimer emission of 1 is found to be enhanced upon the addition of K+ ion which is due to a conformational change of the ligand to have a more efficient pi-pi* interaction of two pyrenes. By contrast, no fluorescence change of 1 was observed in the anion binding test with F-, Cl-, Br-, I-, CH3CO2-, HSO4-, and H2PO4- as their tetrabutylammonium salts in MeCN. Interestingly, it was observed that the excimer emission of the two pyrenes decreases upon the addition of CH3CO2- or H2PO4- in the 1.K+ complex solution. This is presumably due to a conformational change of the ligand by K+ ion binding, which induces the better conformation of two facing pyrene amides to selectively adopt CH3CO2- or H2PO4- ion. This allosterical anion complexation could be applicable for NOR and INHIBIT (INH) logic gates.