Synthesis and complexation behavior of N,N′-bis(1-naphthylmethyl)-1,4,10,13-tetraoxa-7,16-diazacyclo-octadecane

N,N'-Bis(1-naphthylmethyl)-4,13-diaza-18-crown-6 ether (2) gave intramolecular exciplex fluorescence, showing that the excited naphthalene chromophore was quenched by the azacrown unit. The azacrown ether (2) was found to display unique photophysical properties in the presence of metal salts. Complexation of 2 with Ba2+ increased the fluorescence intensity of the host by a factor of 40. H-1 and C-13 NMR analyses of this 1:1 complexation behavior revealed that Ba2+ strongly coordinates with the azacrown nitrogen to cause a dramatic decrease in an intramolecular charge-transfer character. In addition, it was suggested that not only the metal ion-dependent coordinated structure of the resulting complex but also the exchange rate between the free host (2) and its complex with metal ions play a role in controlling the extent of the emission-intensity enhancement that was observed in the presence of a given metal ion.