Researchers develop highly fluorescent polymers with extreme brightness

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In descending order of brightness in the world, there’s the sun and then there’s everything else.

Until now, perhaps.

Researchers from the University of Southern Mississippi’s polymer science department, in collaboration with other scientists, have developed fluorescent solids, creating what they’re calling the brightest known materials in existence – and the groundbreaking discovery could have potential applications in everything from solar energy to medical diagnostics and lasers, to perhaps even autonomous cars.

Professor Yoan Simon from Hattiesburg, Miss.-based University of Southern Mississippi (USM) teamed with Drs. Amar Flood and Krishnan Raghavachari, professors of chemistry at Indiana University and Dr. Bo Wegge Laursen, professor of chemistry at the University of Copenhagen, on the transformative project. USM graduate student Brad Davis assisted in the research at Simon’s lab in the School of Polymer Science and Engineering.

While there are more than 100,000 fluorescent dyes that glow when presented in a liquid form, maintaining the brightness of the colours is much more difficult in solids. That’s because the most commercial fluorescent materials suffer from a phenomenon known as self-quenching, which causes them to lose their properties at high loading, thereby limiting their incorporation into materials. For fluorescent materials to work, they need to be far enough apart – think social distancing, in today’s parlance – but these materials have the natural tendency to aggregate.

“Fluorescence is critical to applications in optical materials including OLEDs and photonics,” the team said in a paper published in the journal Chem. “While fluorescent dyes are potential key components of these materials, electronic coupling between them in the solid state quenches their emission, preventing their reliable translation to applications.”

To solve this long-standing problem, the team developed a universal molecule that allows the dyes to be spaced out, essentially acting like a physical divider. Called small-molecule ionic isolation lattices – or SMILES – this new class of materials perfectly transfer the optical properties of dyes to solids; are simple to make by mixing cationic dyes with anion-binding cyanostar macrocycles; and work with major classes of commercial dyes, including xanthenes, oxazines, styryls, cyanines, and trianguleniums. “Dyes are decoupled spatially and electronically in the lattice by using cyanostar with its wide band gap,” the team said. “Toward applications, SMILES crystals have the highest known brightness per volume and solve concentration quenching to impart fluorescence to commercial polymers. SMILES materials enable predictable fluorophore crystallization to fulfill the promise of optical materials by design.”

Ultimately, the SMILES materials pave the way for the fabrication of polymeric materials with really high chromophore concentration and extreme brightness.

“In some respect, we were the missing piece of the puzzle,” Simon said. “Our collaborators had already developed the chemistry but needed someone who could transfer it broadly into materials. That is where our team came into play.”

Source: University of Southern Mississippi