Metal-Ion Detection by the Magnetic-Field-Sensitive Fluorescence of Intramolecular Exciplexes Containing Aza-Crown-Ether Moieties as Electron Donor

Magnetic field effects (MFE) detected by intramolecular exciplex fluorescence have been studied in acetonitrile solutions for new donor−acceptor compounds in which pyrene is linked to aza-15-crown ether by a polymethylene chain with 3, 9, and 16 CH 2 units. It was found that addition of alkali and alkaline-earth ions to the solutions decreases the observable MFE. The longer the chain and the greater the stability constants of the aza-crown complexes with metal ions, the more pronounced is the influence of the added metal ions. The data obtained are rationalized on the basis of a kinetic scheme that specifically includes photoejection of metal ions from the crown-ether complexes, accompanied by Coulombic interaction of the ions released with the solvent-separated radical ion pairs, the so-called special salt effect.