Molecular Construction, Characterization, and Photophysical Properties of Supramolecular Lanthanide−Calix[4]arene Covalently Bonded Hybrid Systems

Abstract

Hydroxyl groups of the macrocyclic compound p-tert-butylcalix[4]arene have been converted into urethanesil (-NH(C=O)O-)-grafted bridges through a hydrogen transfer nucleophilic addition reaction. Subsequently, the modified macrocyclic derivative can coordinate to lanthanide ions (Tb, Eu) effectively and form a hybrid framework after the cohydrolysis and copolycondensation process through the triethoxysilane components. The above sol-gel-derived inorganic-organic supramolecular hybrids are analyzed under infrared spectroscopy, ultraviolet absorption, and luminescence spectroscopy for interpretation of their photophysical properties. Spectroscopic data point out that the modified calix[4]arene could sensitize diverse lanthanide ions to exhibit attractive green and red luminescence. It is noted that the triplet energy level of this particular macrocyclic bridged ligand is more suitable for the emissive energy level of Tb(3+) ions than the Eu(3+) ions. The luminescent lifetimes and quantum yields of europium hybrids are discussed, and the number of water molecules coordinated to Eu(3+) is estimated.