Chemists say solids don’t get brighter than this

These are 3D printed gyroids made from SMILES (small-molecule ionic isolation lattices), a new class of materials that, according to the chemists who developed them, might just be the brightest in existence.

And that’s possible, they say in a paper in the journal Chem, thanks to a new way of ensuring fluorescent colours don’t fade in solids.

While many fluorescent dyes are on the market, almost none can be mixed and matched in predictable ways to create solid optical materials, says Amar Flood, from Indiana University, US, who led the international project with Bo Laursen, from Denmark’s University of Copenhagen.

Dyes tend to undergo quenching – a decrease in fluorescence intensity – when they enter a solid state, turning brightness into a more subdued glow. “The problem of quenching and inter-dye coupling emerges when the dyes stand shoulder-to-shoulder inside solids,” says Flood. “They cannot help but ‘touch’ each other.”

To overcome this problem, the researchers say, they mixed a coloured dye with a colourless solution of cyanostar, a star-shaped macrocycle molecule that prevents the fluorescent molecules from interacting as the mixture solidified, keeping their optical properties intact.

As the mixture became a solid, SMILES formed, which the researchers then grew into crystals, precipitated into dry powders, and finally spun into a thin film or incorporated directly into polymers.

Since the cyanostar macrocycles form building blocks that generate a lattice-like checkerboard, the researchers could simply plug a dye into the lattice and, without any further adjustments, the structure would take on its colour and appearance.

Previous research has used coloured macrocycles, Flood says, but the colourless ones made all the difference, allowing “the isolation lattice to fully express the bright fluorescence of the dyes unencumbered by the colours of the macrocycles”.

Next, the researchers plan to explore the properties of fluorescent materials formed using their novel technique.

“These materials are totally new, so we do not know which of their innate properties are actually going to offer superior functionality,” says Flood. “We also do not know the materials’ limits.”

But the potential, he says, is enormous, with possible applications “in any technology that needs bright fluorescence or calls for designing optical properties, including solar energy harvesting, bioimaging, and lasers”.