Energy-transfer luminescence of lanthanide ions encapsulated in sensitizer-modified calix[4]arenes

To induce the light-emitting properties of Tb3+ and Eu3+, calix[4]arenes bearing three amide groups (composing a metal-binding site) and one sensitizer group (phenacyl group or diphenacylcarbonyl group) on the lower rim have been synthesized. The high luminescence quantum yields (φ= 0.27 for Tb3+ and 0.061 for Eu3+) were attained by both the metal-encapsulation effect of calix[4]arenes and the selection of a sensitizer with a proper energy gap. The possible energy-transfer mechanisms from the sensitizer group to the encapsulated metal ions are discussed.