In an OLED, the goal is to convert all of the excitons to light, but three-fourths of the created excitons are triplets, which do not produce light in conventional materials, while the remaining one-fourth are singlets, which emit through fluorescence.
Using the heat in the environment to give triplets an energetic boost is sufficient to convert them into light-emitting singlets.
This process, known as thermally activated delayed fluorescence (TADF), is said to occur at room temperature in appropriately designed molecules.
"Many new TADF molecules are being reported each month, but we keep seeing the same underlying design with electron-donating groups connected to electron-accepting groups," says lead researcher Masashi Mamada.
"Finding fundamentally different molecular designs that also exhibit efficient TADF is a key to unlocking new properties."
The mechanism explored by the researchers involves the reversible transfer of a hydrogen atom from one atom in the emitting molecule to another in the same molecule to create an arrangement conducive to TADF.
This transfer occurs spontaneously when the molecule is excited with optical or electrical energy and is known as excited-state intramolecular proton transfer (ESIPT).
The hydrogen transfers back to its initial atom after the molecule emits light, and the molecule is then ready to repeat the process.
According to the researchers, although TADF from an ESIPT molecule has been reported previously, this is the first demonstration of highly efficient TADF observed inside and outside of a device.
This different design strategy could open the door for achieving TADF with a variety of new chemical structures that would not have been previously considered.
