Improve tenfold! Researchers have developed a new type of organic luminescent material, which can assist biological imaging


News on December 27, 2021, recently, a team from the Okinawa Institute of Science and Technology (OIST) has introduced a new method of manufacturing luminous materials that they believe can reduce the reliance on inorganic crystals derived from rare earth materials. The team used the method to create a glow-in-the-dark effect using readily available organic materials.

"Not only are organic materials more readily available and easier to work with than inorganic materials, but they are also soluble, which has the potential to diversify and expand the use of luminous objects as properties can be added to inks, films and textiles," "Another important application is their potential use in bioimaging, which could have myriad benefits for health sciences," said Chihaya Adachi, director of Kyushu University's Center for Organic Photonics and Electronics Research (OPERA).

Glow-in-the-dark materials are used worldwide in emergency signs, watches and paint. Provided by OIST

In 2017, the team demonstrated for the first time that two organic materials can produce a glow-in-the-dark effect. However, the effect is almost 100 times weaker than inorganic methods. To demonstrate the method, the team used ultraviolet light to generate emissions. The effect can only be seen in a dark room, where the sample cannot be exposed to oxygen.

In the current work, the researchers progressed from an approach using two components to one using three components as well as different molecules. The results showed that the emission lasted for more than an hour at room temperature—a tenfold improvement over previous work.

Ryota Kabe, head of OIST's Organic Optoelectronics Division, said: "The process that produces the luminous effect is divided into four stages - charge transfer, separation, recombination, and finally emission. Within a molecule, electrons are located in holes. An important part of the process It's separating the electrons from the holes. When the two recombine, it creates the light."

By tweaking the emission mechanism and the molecules used, the researchers improved the performance of the organic luminescent material by a factor of ten. The resulting emissions lingered in the air at room temperature for more than an hour. Provided by OIST



In the team's previous work, when an organic material is excited by light, electrons are transferred from molecules called electron donors to molecules called electron acceptors. Problems arise, however, when the electron acceptor can no longer store electrons. This recombination creates a glow effect when the electrons return to the donor, but due to the limited number of stored electrons, the glow is less intense and disappears quickly.

In the current work, the researchers used molecules that ensured the movement of holes rather than electrons. This hole-diffusion system reduces the likelihood of molecules reacting with air, ensuring that the sample still emits light when exposed to oxygen. Second, the researchers used hole traps that kept the electrons and holes apart for longer and allowed more holes to build up. The addition of a hole trap additionally increases the resulting discharge cycle.

Finally, the team used molecules that require less energy to move between the different steps of the process. This ensures that the entire process requires less energy and allows emissions to be produced in visible light, not just UV light.

According to Kabe, organic molecules now work in air, but their performance is still weak. The team will continue to adjust the emissions until they are comparable to those produced by inorganic crystals.

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