Encapsulation of Isolated Luminophores within Supramolecular Cages

The sequestration of luminophores within supramolecular polyhedral compartments of a crystalline zeolite-like hydrogen-bonded framework illustrates a unique approach to limiting the self-quenching ordinarily exhibited at the high concentrations achievable in this framework. A range of differently sized luminescent guests, namely coumarin 1, coumarin 4, fluorescein, [Ru(bpy)₃ ]Cl₂ , and rhodamine B, can be encapsulated in amounts of up to one molecule per cage, equivalent to a concentration of 0.175 m, which is significantly higher than the concentration at which aggregation-induced quenching occurs in other media. The luminescence spectra of the encapsulated guests are consistent with the presence of isolated monomers and the absence of self-quenching. The emission color of the single crystals can be tuned readily from blue to red through the choice of guest molecules. These observations promise an approach to organic solid-state lasing compounds if crystals of sufficient size and quality can be prepared.