Helicenes are ortho-fused polycyclic aromatic compounds that adopt a non-planar, screw-shaped geometry. Because the two possible screw senses, designated P for right-handed and M for left-handed, are mirror images of one another, individual helicenes are inherently chiral even though they contain no classical stereogenic center. When several helicene units are woven into a single nanographene scaffold, the relative arrangement of their screw senses matters enormously. An arrangement in which all helices turn the same way produces a molecule with strong chiroptical activity, while a mixed arrangement can partially or fully cancel the chiral response. Until now, preparing these multi-helical architectures with complete stereochemical control has been a formidable synthetic challenge, because forming each helical rim typically generates a mixture of stereoisomers that are difficult to separate.

The new strategy addresses this problem through a modular design in which stereodefined building blocks are assembled stepwise around a central carbon-rich core. By carefully orchestrating the sequence of cyclization reactions, the chemists can dictate whether each helicene adopts the P or M configuration as it forms, rather than relying on statistical mixtures. This converts what was previously an uncontrolled combinatorial problem into a rational synthesis. The approach proved general enough to furnish hexabenzocoronene derivatives, a class of compact disk-like nanographenes, as well as extended graphene nanoribbon segments decorated with up to eight helicene units all twisting in the same direction.

The significance of achieving uniform helix alignment extends well beyond synthetic elegance. Chiral nanographenes interact differently with left- and right-circularly polarized light, producing large circular dichroism signals and, in some cases, circularly polarized luminescence. Materials that emit or absorb circularly polarized light efficiently are of intense interest for next-generation display technologies, optical data storage, spin-selective electronics, and chiral photonics. The intensity of these effects generally scales with the degree of chiral order in the molecule, so a nanographene bearing eight cooperatively aligned helices can display chiroptical responses far stronger than those of a molecule containing a single helicene.

A particularly striking feature of the reported materials is their near-infrared emissive behavior. Near-infrared emission, roughly in the 700 to 1700 nanometer window, is valuable for biological imaging, telecommunications, and optical sensing, yet most organic molecules emit at shorter wavelengths. Rigid, planarized nanocarbon frameworks tend to reduce the energy gap between their ground and excited states, pushing emission toward longer wavelengths, and the appended helicenes in this work appear to contribute both to the red shift and to the chiral character of the emitted light. Because the synthetic strategy is modular, the researchers can adjust the number, position, and handedness of the helicene units and thereby tune the photophysical and chiroptical properties in a predictable manner rather than by trial and error.

The synthetic logic rests on established carbon-carbon bond-forming reactions, notably oxidative cyclodehydrogenation, which fuses adjacent aromatic rings into the extended graphene-like lattice, combined with diastereoselective steps that lock in the helix handedness. In a diastereoselective transformation, the existing stereochemical information within an intermediate biases the formation of a new stereogenic element toward one outcome. In these nanographenes, the first helix to form sets the conformational stage for its neighbors, and subsequent cyclizations follow the templating influence of the pre-existing helical rims. Enantioselective steps, in contrast, distinguish between the two mirror-image pathways from the outset, allowing the chemists to choose globally left-handed or globally right-handed products. Combining both forms of stereocontrol in one sequence is what makes the construction of up to eight aligned helices feasible.

Multi-helical nanographenes of this kind can be described in terms of their diastereomeric relationships: molecules with the same set of helix configurations but different relative arrangements are diastereomers, while a fully right-handed molecule and its fully left-handed counterpart are enantiomers. Distinguishing and characterizing these species requires sophisticated analytical tools. The researchers relied on standard structural confirmation methods common to the field, including nuclear magnetic resonance spectroscopy to probe the aromatic framework, mass spectrometry to confirm molecular formulas, high-performance liquid chromatography on chiral stationary phases to separate and quantify enantiomers, and circular dichroism spectroscopy to measure the chiroptical signatures. Photoluminescence measurements then quantified how efficiently the materials emit light and at which wavelengths.

The broader context of this work is the growing field of chiral nanocarbons, which includes helically twisted graphene nanoribbons, chiral carbon nanotube models, and saddle-shaped or bowl-shaped polycyclic aromatics. These structures bridge molecular chemistry and materials science: they are discrete, well-defined molecules that can be purified and characterized like ordinary compounds, yet their extended pi-conjugated frameworks give rise to the electronic behavior of graphene, one of the most celebrated materials of the past two decades. Introducing controlled chirality into such frameworks adds a functional dimension that achiral nanographenes lack, enabling interactions with polarized light and with chiral biological or chemical environments.

One of the enduring obstacles in this area has been scalability and stereochemical purity. Many beautiful chiral nanocarbon structures have been reported only as racemic mixtures, in which left- and right-handed forms coexist, limiting their usefulness in devices that exploit circularly polarized light. Others required laborious chiral chromatographic resolution that yields only tiny quantities of material. A stereoselective synthesis that directly delivers a single enantiomer or a defined diastereomer, in modular fashion, represents a meaningful step toward practical exploitation. It also allows systematic structure-property studies, since a family of closely related stereoisomers can be compared to isolate the influence of each helical unit on absorption, emission, and chiroptical response.

Looking forward, the modular nature of the strategy suggests extensions in several directions. Varying the substituents on the helicene rims could modulate solubility, packing in the solid state, and supramolecular assembly, all of which are critical for processing these large molecules into thin films for devices. Incorporating heteroatoms such as nitrogen, boron, or oxygen into the nanographene core could further tailor the electronic structure, potentially yielding ambipolar or n-type chiral semiconductors. Longer graphene nanoribbons with patterned helicene arrays might display anisotropic charge transport combined with strong circular dichroism, a combination relevant to chiral spintronics. And because the emission can reach the near-infrared, biomedical applications that demand deep tissue penetration and chiral light-matter interactions become plausible, provided the materials can be made biocompatible. For now, the immediate achievement is conceptual: demonstrating that multiple helical elements in a single nanographene can be installed with deliberate, uniform stereochemistry, converting a class of molecules once accessible only as complicated mixtures into rationally designed, property-tunable materials for advanced optoelectronics.

Subject of Research: Enantio- and diastereoselective synthesis of multi-helical nanographenes

Article Title: Enantio- and diastereoselective synthesis of multi-helical nanographenes

Article References: Shimizu, R., Nogami, J., Kishida, Y., Morita, F., Maeda, C., Uekusa, H., & Tanaka, K. (2026). Enantio- and diastereoselective synthesis of multi-helical nanographenes. Nature Synthesis. https://doi.org/10.1038/s44160-026-01155-9

Image Credits: AI Generated

DOI: 10.1038/s44160-026-01155-9

Keywords: nanographenes, helicenes, stereoselective synthesis, hexabenzocoronenes, graphene nanoribbons, chirality, chiroptical properties, circularly polarized luminescence, near-infrared emission, polycyclic aromatic hydrocarbons, optoelectronic materials, molecular synthesis

The investigation focused on bulk formamidinium lead iodide films, which are a subtype of halide perovskites. What marks this study as especially significant is the fact that these films were produced through scalable solution-based or vapor-phase deposition techniques rather than the highly controlled, specialized growth methods typically employed in laboratories. Such scalability potentially opens the door to practical, affordable development of ultrafast photonic technologies on a commercial scale, circumventing the limitations that often hamper translation from bench to market.

Central to this discovery is the composite nanodomain superlattice structure intrinsic to these perovskite films. Unlike uniform crystals, these materials possess a spatially ordered array of alternating structural domains at the nanoscale. These domains form superlattice arrangements capable of inducing rapid radiative recombination through a mechanism attributed to quantum tunneling effects. The tunneling phenomena enable electron-hole pairs to recombine at unprecedented rates, manifesting in ultrafast transient photoluminescence signals within the material.

The research team, led by Professor Sam Stranks of the Optoelectronic Materials and Device Spectroscopy group, employed a combination of cutting-edge ultrafast spectroscopy techniques alongside advanced optical and electron microscopy characterization. This comprehensive methodological approach allowed them to pinpoint the nanodomain superlattices as the structural origin behind the extraordinary speed of light emission. Such synergy between spectroscopy and microscopy served to correlate the quantum temporal dynamics of the photoexcited carriers directly with the material’s nanostructural features.

One striking aspect of this study is the observation of quantum transients on the order of 2 picoseconds, a timeframe rarely accessible in bulk semiconductors. Conventional optoelectronic materials typically display slower radiative recombination processes due to larger exciton binding energies or less efficient carrier transport. The discovery that halide perovskites can overcome these limitations emphasizes their versatility and underlying quantum mechanical sophistication, pointing toward their potential utility in ultrafast light sources, optical switches, and even components for quantum communication systems.

While these results are exciting, it is crucial to note the conditions under which the experiments were conducted. The ultrafast quantum phenomena were recorded at cryogenic temperatures, which often enhances coherence times and suppresses phonon interactions that may otherwise degrade performance at ambient conditions. The study does not provide data on whether similar ultrafast behavior persists at room temperature, nor does it explore critical quantum-optical properties such as single-photon purity or indistinguishability. These factors are essential to evaluate the suitability of halide perovskites for quantum information applications.

Despite these current limitations, the scalable production methods and the intrinsic nanodomain architecture of formamidinium lead iodide films suggest that further optimization could extend these ultrafast quantum effects into practical operational regimes. The ability to fabricate large-area films with reproducible quantum properties is particularly promising for the development of next-generation photonic devices that demand both high-speed response and cost-effectiveness. Such devices could find applications in telecommunications, sensitive photodetectors, and integrated quantum circuits.

The research contributes significantly to the growing body of knowledge demonstrating that halide perovskites are not just confined to solar energy harvesting but harbor a wealth of multifaceted optoelectronic functionalities. Their structural tunability at the nanoscale facilitates a degree of quantum control previously unattainable in similarly processed materials. This intrinsic link between nanoscale structure and quantum emission marks a paradigm shift in how researchers might approach the design of advanced photonic materials.

Dr. Dengyang Guo, a post-doctoral fellow and joint first author of the paper, emphasized the practical implications of the findings: “Seeing these ultrafast effects in scalable films is exciting. It shows perovskites have even more to offer than we realised, beyond solar cell optimisation.” This insight echoes the broader scientific community’s growing recognition that halide perovskites could represent a platform technology, adaptable across various domains of photonics.

PhD student Tom Selby, who also contributed equally to the research, expressed enthusiasm over the structural-emission correlation: “Being able to trace the emission back to the structure has been an eye-opener – it is really exciting to consider the potential of what this research could lead to.” Such fundamental understanding paves the way for rational engineering of these materials to tailor ultrafast quantum responses for specific device applications.

Professor Sam Stranks summarized the broader vision behind the work: “Perovskites continue to surprise us. This discovery shows how their intriguing nanoscale structure gives rise to intrinsic quantum properties that could be harnessed for future photonic technologies.” These advances suggest that the perovskite family may well become a cornerstone of emerging quantum photonic devices, provided ongoing research overcomes challenges related to material stability and room-temperature operation.

In conclusion, this investigation into picosecond quantum transients within halide perovskite nanodomain superlattices highlights a frontier where materials science meets quantum photonics. By leveraging scalable fabrication routes and elucidating the fundamental mechanisms behind ultrafast emission, the study marks an essential step forward in the quest for highly efficient, low-cost quantum light sources and photonic components. The continued exploration of halide perovskites, at both the fundamental and applied levels, is poised to unlock exciting opportunities in both classical and quantum photonic device architectures.

Subject of Research: Quantum transients and ultrafast photonics in halide perovskite nanodomain superlattices

Article Title: Picosecond quantum transients in halide perovskite nanodomain superlattices

News Publication Date: 29-Oct-2025

Web References: 10.1038/s41565-025-02036-6

Keywords: Perovskites, semiconductors, renewable energy, solar energy, quantum transients, ultrafast photonics, nanodomain superlattices, quantum tunneling, radiative recombination, scalable materials, optoelectronics