Revolutionizing π-Molecules: A Novel Design Strategy Transforms Organic Semiconductor Materials

A groundbreaking advancement in the field of organic electronics has been achieved by a collaborative research team from the Institute for Molecular Science (IMS), SOKENDAI, and Kyoto University’s Institute for Chemical Research. The scientists have synthesized unique three-dimensionally shaped π-conjugated molecules, which incorporate an innovative internal twist within their molecular architecture. This novel structural feature contributes to a revolutionary three-dimensional charge transport mechanism, which marks a significant departure from the conventional planar molecular designs widely used in organic semiconductors. The work offers fresh insights into how manipulating molecular geometry at the atomic level can drastically reshape electronic behaviors, potentially transforming the future of flexible and lightweight electronics.

Organic semiconductors, known for their lightweight and flexible properties, have long attracted attention as candidates for next-generation electronics that are more environmentally sustainable compared to traditional inorganic semiconductors. However, the predominant molecular frameworks in organic electronics rely heavily on planar molecules, which confine charge transport pathways to two-dimensional planes. Such planarized structures necessitate precise molecular orientation during device fabrication to ensure optimal charge mobility and device performance. This orientation dependence presents a formidable engineering challenge and limits the versatility and scalability of organic electronic devices.

Addressing this fundamental limitation, the research team introduced methyl substituents into molecules comprised of multiple thiophene units, which are sulfur-containing five-membered heteroaromatic rings well-known for their excellent electronic properties. The strategic placement of these methyl groups enforces a twisted conformation in the π-conjugated backbone, effectively warping the molecule out of planarity. This pronounced internal twist facilitates an unprecedented three-dimensional stacking arrangement in the solid state, verified through advanced X-ray crystallographic techniques. Such stacking leads to enhanced π-π interactions extending in multiple spatial directions, forming a three-dimensional charge transport network, rather than being restricted to a single plane.

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The implications of this three-dimensional molecular assembly are profound for the field of molecular electronics. Computational modeling and charge transport pathway analysis revealed that holes—the primary positive charge carriers in organic semiconductors—could migrate through multiple trajectories within the solid matrix. This contrasts markedly with planar organic semiconductors, where charge transport is predominantly one or two-dimensional. The multidimensional charge percolation network promises to alleviate the stringent need for molecular orientation control in electronic device manufacturing, thereby simplifying fabrication processes and enhancing device reliability and uniformity.

To experimentally validate the semiconducting properties of these twisted molecules, the researchers fabricated organic field-effect transistors (OFETs) utilizing the synthesized compounds as the active channels. OFETs serve as crucial evaluation platforms for organic semiconductors due to their ability to induce and measure charge carrier mobility within thin organic layers. The twisted molecules demonstrated a hole mobility on the order of 1.85 × 10⁻⁴ cm² V⁻¹ s⁻¹, an unambiguous indicator of their functional capability as organic semiconductors. Although this mobility value is modest compared to some state-of-the-art planar organic materials, the results signify an important proof of concept underscoring the feasibility of three-dimensional charge transport in twisted molecular architectures.

Delving deeper into the structural origins of this unique electronic performance, X-ray crystallographic data confirmed that the introduction of methyl groups led to a highly twisted π-conjugated core. This twist disrupted conventional π-π stacking and induced multi-directional interactions among molecules in the crystal lattice. Such controlled geometric distortion not only retained electronic conjugation but also spatially oriented molecular orbitals to overlap in three dimensions. This molecular engineering highlights a novel paradigm in organic semiconductor design, where deliberate conformational twisting produces desirable electronic pathways unavailable in flat molecular analogs.

The intrinsic chirality derived from the twisted molecular configuration adds an additional layer of complexity and potential functionality. Chirality in organic electronic materials can influence how charge carriers behave, interact with polarized light, and participate in spin-selective processes, which may open doors toward advanced applications such as chiral optoelectronics and spintronic devices. Moreover, chiral three-dimensional molecular architectures could inspire future exploration of enantiomer-specific charge transport mechanisms and their integration in multifunctional devices.

The research team’s results also bring forth a promising solution to the persistent challenge of device-level orientation control. Conventional planar organic semiconductors require exacting alignment to optimize charge transport directionality, which hampers manufacturing scalability and yields variability. Twisted molecules capable of supporting charge migration in three spatial dimensions considerably mitigate this orientation constraint. Manufacturers could realize flexible electronics with reduced sensitivity to processing conditions, facilitating the production of robust, large-area devices with consistent performance metrics.

Beyond this immediate application, the synthesis of twisted π-conjugated molecules bears broad ramifications across organic synthesis and material science disciplines. The methodology and principles established here suggest that other heterocyclic units and substitution patterns may be tailored to further modulate the extent of twisting and electronic properties. Such molecular versatility could accelerate the discovery of new classes of organic semiconductors, optimized for various functionalities such as high mobility, stability, and tunable band gaps.

Computational investigations accompanying the experimental work have provided vital insights into the charge transport dynamics within these three-dimensional frameworks. Advanced simulations clarified how the aggregate structure facilitates hole migration via interconnected pathways formed by overlapping molecular orbitals. These predictive models serve as essential tools for rational material design, enabling researchers to visualize and quantify the effects of molecular twisting on electronic performance before actual synthesis. This synergistic approach of combining theory and experiment is rapidly becoming indispensable in the quest for high-performance organic electronic materials.

The study also exemplifies the fruitful collaboration between experienced researchers and graduate students, fostering an environment of innovative scientific discovery. By bridging expertise in organic synthesis, crystallography, computational modeling, and device engineering, the team navigated complex interdisciplinary challenges, culminating in a publication that pushes the boundaries of organic semiconductor technologies. Their findings were disseminated via the Royal Society of Chemistry’s prestigious journal Chemical Communications on June 19, 2025, signaling a notable milestone in the evolution of molecular electronics.

Looking forward, the research opens several exciting avenues for continued exploration. Enhanced molecular designs could focus on increasing charge carrier mobilities, improving the environmental and thermal stability of the twisted molecules, and integrating these materials into diverse device architectures beyond OFETs, such as organic photovoltaics, light-emitting diodes, and sensors. Additionally, investigating the interplay between three-dimensional π-π interactions and device performance under mechanical strain may advance flexible and stretchable electronics, key areas for wearable and biointegrated technologies.

In conclusion, the creation and characterization of twisted π-conjugated molecules with inherent three-dimensional stacking represent a paradigm shift in organic semiconductor science. This innovative structural design fundamentally challenges the conventional wisdom favoring planar molecules, instead demonstrating that molecular twisting can be harnessed to enable three-dimensional charge transport. Ultimately, this breakthrough paves the way for the development of next-generation electronic devices that are not only efficient and flexible but also easier to manufacture, offering sustainable solutions that align with the demands of future technology landscapes.

Subject of Research: Not applicable

Article Title: Synthesis, structure, and properties of twisted π-conjugated molecules featuring three-dimensional π-π interactions in solid states

News Publication Date: 19-Jun-2025

Web References:
https://doi.org/10.1039/D5CC02387D

References: Article published in Chemical Communications, Royal Society of Chemistry, 19 June 2025.

Image Credits: Not specified

Keywords

Organic semiconductors, transistors, molecular electronics, carrier mobility, chirality, organic synthesis

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