Functionalization of Calix[4]arene as a Molecular Bridge To Assemble Luminescent Chemically Bonded Rare-Earth Hybrid Systems

The functional macrocyclic precursors (abbreviated as BC[4]Si and C[4]Si) derive from two kinds of calix[4]arenes, p-tert-butylcalix[4]arene (BC[4]) and calix[4]arene (C[4]) grafted by 3-(triethoxysilyl)propyl isocyanate (TESPIC) through base-initiated nucleophilic addition, and then three series of novel luminescent chemically bonded hybrid material systems (BC[4]Si, RE-BC[4]Si, C[4]Si, and RE-C[4]Si, where RE = Eu, Tb) with organic parts covalently linked to inorganic parts via the functionalized calix[4]arene linkages have been assembled by a sol-gel process, which is characterized by the X-ray diffraction, thermogravimetry/differential scanning calorimetry, scanning electron microscopy, and spectroscopy. It is found that the coordination of rare-earth ions has an influence on the organization and microstructure of the hybrid systems. The photoluminescent behavior (luminescence, lifetime, quantum efficiency, and energy transfer) for these chemically bonded hybrids is studied in detail. Three color luminescences are checked, blue (BC[4]Si and C[4]Si), green (Tb-BC[4]Si and Tb-C[4]Si), and red (Eu-BC[4]Si and Eu-C[4]Si), respectively, suggesting that the intramolecular energy-transfer process between the rare-earth ion and the host takes place within these molecular-based hybrids. Also, especially their quantum efficiencies are determined, which indicates that the different hybrid material systems derived from different functionalized calix[4]arene bridges present different luminescence behavior.