A light-emitting molecule can be characterised in fine detail, from emission spectra to lifetimes and quantum yields, and still leave the main question open: why does it behave that way? For a heavy-atom-free carbazole emitter with delayed dual emission, the answer lay in how the molecules pack in the solid, and reaching it needed a crystal structure that conventional methods could not provide.
The emitter is a carbazole hexamer. Like many organic electronic materials, its crystals stay in the sub-micrometre range, well below what single-crystal X-ray diffraction can use. In the study now published in Advanced Optical Materials, Thomas, Hariharan and co-workers used 3D electron diffraction (3D ED) to solve the structure directly from those small crystals. The 3D ED data were measured at ELDICO on the ED-1.
That structure was the missing piece. Combined with ultrafast spectroscopy and computation, it linked the emission behaviour to the way the molecules are arranged, turning a structure-property question into a basis for designing the next emitter.
There is a general point here. Optical measurements show what a material does, and computation suggests what it might do, but the crystal structure fixes both to what is actually present. When the crystals are too small for X-ray, that is often the piece that is missing, and 3D ED supplies it.
Why it matters for materials & photonics
Organic emitters for OLEDs and related applications are often developed from solution behaviour and thin-film performance, with the solid-state structure inferred rather than measured, because the crystals rarely reach X-ray size. 3D ED changes that. Sub-micrometre crystals are enough, so packing effects on emission can be studied directly instead of modelled around them.
The paper, 3D electron diffraction uncovers the structural origin of delayed dual emission, appears in Advanced Optical Materials, e00022 (2026), doi:10.1002/adom.202600022. See all ELDICO publications.