Energy-Transfer Luminescence of Lanthanide Ions Encapsulated in Calix[4]arenes. Correlation between the Energy Level of Sensitizers and the Quantum Yield

It was shown that the Tb3+ and Eu3+ complexes of 5,11,17,23-tetraacetyl-25,26,27,28-tetrakis(N,N-diethylaminocarbonylmethoxy)calix[4]arene give the high luminescence quantum yields (Φ = 0.164 for Tb3+ and 0.017 for Eu3+). The mechanistic investigations established that the high quantum yields are due to the energy level suitable to the energy-transfer and the presence of the carbonyl groups which mediate the intersystem crossing.