Study of the luminescence of Eu(III), Tb(III) and Gd(III) cryptates containing Py(CO2Et)2 as ligands

It has been synthesized the [Ln⊂bpy.bpy.py(CO2Et)2]3+ cryptates, where Ln=Eu, Tb and Gd. These compounds have been characterized through usual methods and their luminescences have been quantified through spectroscopic measurements such as luminescence lifetime, emission spectrum and emission quantum yield, q. The experimental q value obtained for the [Tb⊂bpy.bpy.py(CO2Et)2]3+ cryptate has been compared to one of the [Eu⊂bpy.bpy.py(CO2Et)2]3+ cryptate, giving q=25% for the former and q=14% for the latter, both in aqueous solution at 300 K. The theoretical q value calculated for the Eu(III) cryptate was 19%, being in a very good agreement to the experimental one. The results indicate that the theoretical model which has been used to study the luminescence of complexes can also be satisfactorily applied to cryptates and the design of new ligands with high-energy triplet states should give very efficient light converting molecular devices when the central ion is the Tb(III).