Ann Arbor Times

A study led by the University of Michigan has introduced a new blue fluorescent molecule that achieves high emission efficiencies in both solid and liquid states. This development could have significant implications for technology and medicine.

Fluorophores, which are molecules that absorb light and emit it at lower energy levels, play a crucial role in OLED displays and medical diagnostics. They need to be effective in solid form for display applications and in liquid form for biological uses. The new fluorophore, however, functions well in both forms.

"The fluorescent material reached record-breaking brightness and efficiency with 98% quantum efficiency in the solid state and 94% in solution," stated Jinsang Kim, the Raoul Kopelman Collegiate Professor of Science and Engineering at U-M's Department of Materials Science and Engineering. The study is published in Nature Communications.

Typically, engineers encounter challenges when transitioning fluorophores from solution to solid-state applications due to molecular interactions. "Fluorophores behave very differently in the solid state, which then requires more rational molecular engineering effort for structural modification," Kim explained. The research established a design principle aimed at reducing development time and cost for future applications.

The discovery of this versatile fluorophore—named TGlu—was unexpected for lead author Jung-Moo Heo, a postdoctoral research fellow at U-M. "TGlu was an intermediate step for another chemical design, but during purification I found it was surprisingly highly emissive," Heo said.

The team developed a simple design featuring a single benzene ring core with donor groups across from acceptor groups on the ring. This quadrupolar structure symmetrically distributes charge across the molecule, stabilizing emission across various environments.

Despite its small size limiting overall conjugation length, TGlu emits blue light due to its wide absolute energy gap. Typically associated with efficiency drawbacks due to heat loss, this molecule minimizes such losses through an Inverted Energy Gap Law confirmed by experiments and simulations.

In solid states, bulky acceptor groups prevent quenching by keeping molecules apart. Additionally, TGlu is simple to produce through three steps, enhancing scalability while reducing costs.

While currently emitting blue light, researchers plan to adjust the band gap to change color output. Further testing under electrical excitation is necessary due to additional loss mechanisms. Future work includes developing a phosphorescent version of TGlu for use in display technology.

Contributors to this research include institutions such as Autonomous University of Madrid, University of Valencia, Eberhard Karls University Tübingen, and Seoul National University.