Metal ion enhanced phosphorescence of 2,3-naphtho-10-aza-15-crown-5: A possible molecular photonic operator

Abstract

A novel crown ether, 2,3-naphtho-10-aza-15-crown-5 (NAC) was synthesized. This compound does not show strong fluorescence and phosphorescence due to photoinduced intramolecular electron transfer from the nitrogen lone pair of electrons to the singlet excited state of the naphthalene chromophore. Complexation with heavy-metal ions results in the quenching of the fluorescence and enhancement of the phosphorescence significantly. These observations were interpreted in terms of the binding interactions, between the nitrogen lone pair electrons and the metal cation, which prevent photoinduced intramolecular electron transfer, and the heavy-atom effects which induce quenching of the fluorescence and enhancement of the phosphorescence. These azacrown and heavy-metal-based systems could be useful as potential chemical sensors and molecular photonic devices.