Applications of small-molecule chirality
of technology, including in optics and filters, in spectroscopy and to encode information. Thus, it is attracting growing interest for applications such as quantum computing [9], 3D displays [10] and bioimaging [10]. Owing to the rapid commercial expansion of OLED displays ( Figure 2 ) [12], a highly promising field is the development of circularly polarized OLEDs (CP-OLEDs). These devices generate circularly polarized electroluminescence directly, a feat that can only be achieved using a chiral light-
emitting layer [13]. In OLED displays, an antiglare polarizing filter (linear polarizer and quarter-wave retarder [14]) is placed on top of the display to block reflected light from the environment which would otherwise wash out the image ( Figure 3 ) [14]. When ambient light (like sunlight) strikes the surface, the linear polarizer filters out randomly polarized light, allowing only the light polarized parallel to its transmission axis to pass through. This linearly polarized light then enters the quarter-wave retarder, where it is transformed into circularly polarized light. The handedness of the
circular polarization— whether left-handed or right-handed—depends
Figure 2 OLED layer structure
on which polarization component is delayed by the retarder. When this light reflects off surfaces such as glass or metal, its handedness reverses. Because circular polarizers block the opposite handedness,
Figure 3 Glare reduction filter
the reflected light cannot pass back through the filter. In practice, this means circular polarizers effectively suppress reflections and are highly useful for reducing glare in display technologies. However, this solution comes at the cost of efficiency. In conventional OLED displays, the light emitted from the OLED pixel is unpolarized, this means 50% of the OLED’s light output is lost in the process [15], since the filter only allows one polarization of light passing through. This inherent trade-off explains the motivation to develop chiral OLEDs (CP-OLEDs) , which emit circularly polarized light directly and could significantly reduce energy losses while maintaining high image quality.
The design flexibility comes from the stereogenic diversity of small molecules: not only point chirality , but also axial, helical, inherent and planar chirality [16] ( Figure 4 ) [2] , each capable of coupling electronic transitions with molecular handedness to yield polarized light.
Figure 4
Efforts to achieve direct circularly polarized (CP) electroluminescence in fluorescent OLEDs have largely used chiral polymers or oligomers
Figure 5 Examples of chiral molecules used in CP-OLEDs
with pendant side chains ( Figure 5a ) [2] , producing dissymmetry factors ( |𝑔 𝐸𝐿 | ) as high as 0.35 through the formation of cholesteric helical stacks [17, 18]. Another promising strategy is the use of chiral
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