Flexible Shape-Changing Molecules Efficiently Emit Orange-to-Red Light for OLED Displays

An international research team led by the University of Osaka has demonstrated that flexible, shape-changing molecules can efficiently emit orange-to-red light without being locked into rigid structures, providing a new design framework for light-emitting technologies. Organic light-emitting diodes, or OLEDs, convert electrical current into light to drive colorful displays on consumer devices such as televisions, computer monitors, and smartphones. Although the electronics industry actively seeks metal-free materials that emit across the full visible spectrum, creating metal-free emitters that efficiently produce orange-to-red light has historically remained a significant technical challenge.

Many existing high-performance OLED systems rely on emitter molecules built around expensive metals such as platinum or iridium. To eliminate these scarce elements, researchers have focused on metal-free compounds operating through thermally activated delayed fluorescence, or TADF. One promising subclass functions via through-space charge transfer, wherein charge moves through open space between electron-donating and electron-accepting molecular components positioned face to face. Previous design paradigms required rigid molecular skeletons to keep these opposing components aligned, leaving the emissive behavior of flexible molecules capable of rearrangement unresolved.

In an experimental study published in the Journal of the American Chemical Society, the Osaka-led team designed large, complex molecules configured in an S shape to evaluate conformational flexibility. In these structures, two electron-donating units and a central electron-accepting unit are connected by rotatable linkages. Unlike previously reported rigid systems, the rotatable connections permit the molecules to adopt multiple geometric conformations, including spatial arrangements where the donor and acceptor units stack closely together in configurations suitable for through-space charge transfer. Theoretical quantum calculations confirmed that the molecules maintain the electronic properties required for through-space charge transfer without permanent conformational locking.

To investigate the light-generation mechanism, the researchers combined time-resolved spectroscopy with quantum chemical calculations. Lead author Nae Aota explained that light emission in these materials is governed both by the variety of conformations the molecules adopt prior to light absorption and by the structural rearrangements that occur after photoexcitation.

When fabricated into functional OLED devices, the flexible emitters generated orange-to-red light with an external quantum efficiency reaching up to 15 percent. Senior author Youhei Takeda noted that the highest-performing device retained high efficiency even under elevated brightness levels, representing a competitive performance standard for metal-free orange-to-red emitters. The findings were achieved in collaboration with European partners, including Professor Przemyslaw Data under the Horizon Europe initiative and Professors Marc Etherington and Piotr de Silva through the Japan Science and Technology Agency’s ASPIRE program.

By establishing that structural flexibility can replace rigid conformational constraints, the study provides fundamental insight into the relationships connecting molecular geometry, dynamic rearrangement, and photoluminescence. The researchers anticipate that extending this conformational adaptation strategy will facilitate the development of efficient TADF materials that emit at longer wavelengths, with potential future applications in consumer display screens and biological imaging systems.

Subject of Research: Flexible light-emitting molecules for organic light-emitting diodes

Article Title: Molecules in motion provide a new way to light up screens

Article References: Molecules in motion provide a new way to light up screens. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: OLEDs, thermally activated delayed fluorescence, through-space charge transfer, light-emitting materials, molecular flexibility, organic electronics, spectroscopy, University of Osaka, Molecules, motion, provide, light