Synthesis of Novel Luminescent Double-Decker Silsesquioxanes Based on Partially Condensed TetraSilanolPhenyl POSS and Tb³⁺/Eu³⁺ Lanthanide Ions

In this study, novel lanthanide-containing double-decker polyhedral oligomeric silsesquiox-anes (POSS) were prepared by combining the partially condensed TetraSilanolPhenyl POSS with terbium (Tb³⁺ ) and europium (Eu³⁺ ) ions. This open-cage POSS possesses four diametrically opposite silanol groups that are able to coordinate, under mild conditions, different luminescent ions through a simple corner-capping method. The two metal-containing POSS functionalized with Tb³⁺ and with an equimolar combination of Tb³⁺ and Eu³⁺ show a completely condensed structure with different luminescent properties. Their emission features depend on the chemical nature of the metal ions incorporated in the framework. An improved stokes shift was detected in the bimetallic compound containing both the Tb³⁺ and Eu³⁺ ions, promoted by the occurrence of a Tb³⁺ →Eu³⁺ energy transfer mechanism. These characteristics identify this metal-functionalized silica platform as a potential candidate for the development of novel luminescent devices.