Since the discovery of the first dye over 150 years ago, fluorescence has revolutionized the scientific community, allowing for new methodology with sensing, imaging, and labeling. One remaining struggle is moving dyes from dilute solution to the solid state. Spectral shifts and emission quenching prevent the formation of predictable fluorescence materials. Many methods have been explored to prevent fluorescence quenching in the solid state, such as aggregation induced emission (AIE) and dilution in polymers. These methods can offer bright fluorescence, however none of these offer a simple universal method for restoring the fluorescence of small molecules in the solid state. We discovered a new material, small-molecule ionic isolation lattices (SMILES), which allow fluorophores to retain bright predictable emission in the solid state. SMILES depends on two design principles: spatial and electronic isolation of each dye from its neighbors. We meet these requirements by reliable crystal engineering. We utilize an ionic lattice of cationic dyes paired with anion receptors. We also need to ensure that the electronic energy levels of the anion-receptor complex isolate the dyes. Here we present the design rules and expansion of our fundamental understanding of SMILES.

Universal engineering of small organic dyes into fluorescent crystals by hierarchical assembly

2019 Fall National Meeting

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