Japanese chemists discover fluorescent compound that could boost device screens efficiency

RIKEN chemists in Japan have discovered a fluorescent organic compound that avoids "Hund’s rule," a quantum-mechanical principle that has limited the energy efficiency of organic light-emitting diodes (OLEDs) for nearly a century, and which could lead to major advances in OLED technology.

According to a release by RIKEN, previous strategies to improve the energy efficiency of OLEDs focused mainly on reducing the energy difference between the light-emitting and non-light-emitting states, but all fluorescent compounds discovered until now have still obeyed Hund’s rule. 

Now, researcher Yong-Jin Pu and his colleagues at the RIKEN Center for Emergent Matter Science have discovered an organic compound in which the two states’ energies are flipped, allowing all molecules to fluoresce and advance the potential quantum energy efficiency of OLEDs to reach 100%, far beyond the current limit of 25%.

The compound was discovered through computer simulations of nearly 35,000 compounds based on the molecule heptazine, which consists of three rings of carbon and nitrogen atoms. 

Pu and his research team synthesized two blue-fluorescent compounds from a list of about 5,250 promising compounds, with one of them defying Hund’s rule, to the surprise of researchers.

“Even after we published this paper, researchers in the field have had a hard time believing this phenomenon because the molecule is so special,” Pu said. “To be honest we don’t know why it works. We found this phenomenon experimentally, but we still don’t know its mechanism. That’s something we intend to explore.” 

The team is currently working with a company to commercialize the technology, which could find applications in lighting, lasers and displays. The team demonstrated the usefulness of their compound by using it to realize an OLED device that had a quantum energy efficiency of 85%, RIKEN reported.

The potential for the compound to revolutionize the display industry cannot be overstated, the release added. Currently, displays in mobile devices are highly wasteful, but with the potential for 100% quantum energy efficiency, OLEDs could become more sustainable. 

That discovery could have implications for lighting and laser technology, with the potential for more energy-efficient and cost-effective applications. 

Research by Pu and his colleagues was published in the journal Nature. The team plans to continue studying the compound to better understand its mechanism and explore its potential applications.