(1,6)Pyrenophanes containing crown ether moieties as fluorescence sensors for metal and ammonium ions. Formation of sandwich, dumbbell, and pseudorotaxane complexes

Abstract

(1,6)Pyrenophanes 1 and 2 in which 1,6-positions of pyrene are bridged with respective tri- and tetra-ethylene glycol chains were synthesized. Addition of Ba(ClO₄)₂ to a 10⁻⁵ M CH₂Cl₂ : CH₃CN = 1 : 1 solution of 1 reduced the intramolecular excimer emission with a maximum at 480 nm and increased the monomer emission around 370–400 nm. In contrast, addition of Ba(ClO₄)₂ to the solution of 2 shifted the intramolecular excimer emission to shorter wavelengths. Addition of n-Bu₂NH₂⁺PF₆⁻ to the solutions of 1 and 2 both decreased the intramolecular excimer emission and increased the monomer emission. Based on the results of these fluorescence changes, Job's plots, and NMR titration, it is concluded that 1 forms a 1 : 1 sandwich-type complex with Ba²⁺, 2 forms a 1 : 2 dumbbell-type complex with Ba²⁺, and both 1 and 2 form pseudorotaxanes with n-Bu₂NH₂⁺. It was also found that when the pyrenophanes 1 and 2 were mixed with tetracyanoethylene (TCNE) in CH₂Cl₂, charge-transfer (CT) complexes were formed, that exhibited absorption maxima at 740 and 744 nm, respectively.