Molecular-recognition-assisted pKa shifts and metal-ion-induced fluorescence regeneration in p-sulfonatocalix[6]arene-encapsulated acridine.

The host-guest interactions of cationic (AcH(+) ) and neutral (Ac) forms of the dye acridine with the macrocyclic host p-sulfonatocalix[6]arene (SCX6) were investigated by using ground-state absorption, steady-state and time-resolved fluorescence, and NMR measurements. The cationic form undergoes significant complexation with SCX6 (Keq =2.5×10(4)  M(-1) ), causing a sharp decrease in the fluorescence intensity and severe quenching in the excited-state lifetime of the dye.