Rewrite New co-assembly strategy unlocks robust circularly polarized luminescence across the color spectrum this news headline for the science magazine post

Researchers at the College of Design and Engineering (CDE) at the National University of Singapore (NUS) have developed a supramolecular co-assembly platform that produces chiral soft materials with strong and stable full-colour circularly polarised luminescence (CPL) across the visible spectrum, including in red, which has historically been a difficult target.

The resulting structures are tunable, scalable and retain their chiroptical properties for over 100 days at room temperature, while withstanding repeated thermal cycles without degradation.

“The chiroptical strengths of the materials are among the highest ever reported. These features make the materials a strong candidate for next-generation chiral optoelectronic devices, including 3D displays, quantum photonic circuits and anti-counterfeiting technologies,” said Professor Lin Zhiqun from the Department of Chemical and Biomolecular Engineering at CDE, who led the study.

The team’s findings, published in Science on 14 August 2025, demonstrate how molecular chirality can be transferred stepwise, from small chiral molecules to polymer chains, and onwards to large-scale supramolecular structures that exhibit strong, stable optical effects.

Self-organising building-blocks

Chirality, like right- and left-handedness, is a property where an object cannot be superimposed on its mirror image. In materials science, chirality influences how light interacts with matter. One example is CPL, a type of light emission where the electric field vector rotates around the direction of propagation.

CPL is valuable for controlling the spin and polarisation of emitted photons — an essential requirement in advanced photonic, electronic, spintronic and biomedical applications. However, creating materials that reliably emit CPL in different colours, particularly at longer wavelengths such as red, remains a challenge.

The researchers developed a new strategy to address this by designing supramolecular structures, which are materials made by the co-assembly of molecules into larger, ordered forms. They started with achiral, star-shaped block copolymers known as PAA-b-PS, which form single-molecule micelles in solution. These were then combined with a simple chiral molecule, R- or S-mandelic acid, which binds to the polymers via hydrogen bonding.

Upon thermal annealing, the polymer-additive mixture self-organised into belt-like nanostructures and eventually into chiral fibre-like structures several micrometres wide. The handedness of the fibres (left- or right-handed) depended on the specific type of mandelic acid used. This hierarchical assembly process enabled the transfer of chirality from small molecules to large, visible-scale structures.

These assembled structures exhibited strong chiroptical responses across both ultraviolet and visible wavelengths, a feature that points to supramolecular chirality rather than molecular chirality. This is crucial as many practical applications, from display technologies to optical sensors, operate in the visible spectrum. Supramolecular organisation allows these materials to function in regimes beyond the reach of conventional molecular chirality, thus expanding their utility in real-world photonic devices.

The researchers also found that the materials were nearly twice as stiff and hard as those without the chiral additive. This added mechanical durability is beneficial for device integration, for instance in flexible or wearable components.

To demonstrate practical functionality, the team incorporated various achiral luminescent dyes (red, green, blue) into the co-assembled polymer framework. The dyes were anchored via hydrogen bonding and adopted the chirality of their environment during co-assembly, resulting in CPL in all three colours.

Notably, this full-colour CPL capability is rare, with red emission being especially difficult to achieve. In this system, the polymer matrix enabled chirality transfer and also passivated the dye molecules, leading to brighter, longer-lasting light with higher quantum yields compared to the same dyes used alone.

“The ability to produce strong CPL across the visible spectrum broadens the scope for practical applications, particularly in photonic devices that require low optical losses and high signal discrimination,“ added Prof Lin.

When more is less

Apart from their ability to generate CPL, the materials also offered a surprising degree of control over their optical behaviour. Adjusting factors such as polymer concentration and the choice of solvent, the NUS researchers were able to invert the handedness of the resulting supramolecule structures, as well as the direction of emitted circularly polarised light.

At low concentrations and in slow-evaporating solvents like dimethylformamide, the co-assemblies formed fiber-like structures with predictable chirality. In contrast, higher concentrations and fast-evaporating solvents like toluene led to kinetically trapped structures with reversed handedness. This chirality inversion was confirmed using both experimental characterisation and molecular dynamics simulations.

“The chirality inversion demonstrates how fine-tuning external factors like solvent composition and concentration can affect supramolecular outcomes,” Prof Lin explained. “This level of control is crucial for designing materials with switchable or programmable optical properties.”

The co-assembly platform developed by the NUS team introduces a scalable and versatile method for synthesising CPL-active materials that combine high chiroptical activity, long-term stability, mechanical strength and colour tunability. The hierarchical structures retain their chiroptical properties for over 100 days at room temperature and withstand repeated heating-cooling cycles without degradation.

“These features are important for enabling the development of next-generation chiral optoelectronic devices, including 3D displays, quantum photonic circuits and anti-counterfeiting technologies. Their robust mechanical properties further support their suitability for device integration,” said Prof Lin.

The researchers are now investigating more complex chiral co-assemblies by tuning the geometry of nonlinear block copolymers, such as dendritic and bottlebrush architectures, and integrating new functionalities, including conductivity, thermo- and light-responsiveness, magneto-chiroptical effects and CPL-active near-infrared emission. These directions could lead to new applications in chiroptoelectronics, sensors, information technology and spintronics.

Read more about his team’s work at: Nanostructured Materials for Energy (NanoME)