Researchers from the Max Planck Institute, National Center for Nanoscience and Technology in Beijing, University of Warsaw, TUD Dresden University of Technology, University of Münster, Sichuan University, Friedrich-Alexander-Universität Erlangen-Nürnberg, Empa and Chinese Academy of Science have developed a cyclophane-based molecular shielding strategy that enables the isolation of individual graphene nanoribbons (GNRs) while simultaneously tuning their optoelectronic properties.
Graphene nanoribbons' practical use has long been limited by strong π–π stacking interactions that drive aggregation into bundles, masking intrinsic properties and preventing reliable integration into single-ribbon devices. To address this, the team designed cyclophane-type bridges that sterically shield the GNR backbone while introducing controlled internal strain. Three cyclophane-shielded GNRs (CsGNRs), labeled 1a–c, were synthesized with different tether lengths (benzene–C20–benzene for 1a, C20 for 1b, and C14 for 1c). These structures were derived from ethynyl-substituted cyclopentadienone-based cyclophane monomers, alongside model nanographenes (2a–c) based on a hexa-peri-hexabenzocoronene core.
Structural analysis highlights the dual role of the cyclophane bridges. In the case of the shortest bridge (C14, compound 2c), single-crystal X-ray measurements reveal a strongly bent architecture with an end-to-end angle of 37.3° and a separation of approximately 0.4 nm between the tether and the aromatic core - significantly exceeding typical π–π stacking distances. This steric barrier effectively suppresses inter-ribbon interactions, enabling true single-ribbon dispersion.
As a result, CsGNR 1c exhibits excellent solubility in N-methyl-2-pyrrolidone, reaching concentrations up to 0.03 g l−1, while avoiding aggregation. This improved dispersibility allows direct investigation of intrinsic properties and supports solution-based device fabrication.
The induced backbone strain also leads to measurable changes in electronic structure. Compared to longer-bridge analogues, 1c shows a widened optical bandgap of 2.0 eV (an increase of 0.2 eV versus 1a and 0.06 eV versus 1b), along with a blue-shifted absorption and pronounced concentration-dependent emission behavior.
Charge transport measurements further reveal the impact of cyclophane-induced strain. Optical pump–terahertz probe spectroscopy shows that short-range charge carrier mobility increases from 190 cm² V−1 s−1 in 1b to 330 cm² V−1 s−1 in 1c - an improvement of up to 74%. This enhancement is attributed to a reduced effective mass and longer scattering time, both arising from the increased backbone bending.
Importantly, the availability of singly dispersed nanoribbons enables device-level demonstrations. Single-electron transistors fabricated using 1c exhibit clear Coulomb blockade behavior at low temperatures, confirming controlled single-electron transport and highlighting the suitability of these materials for quantum electronic applications.
Beyond demonstrating a practical route to isolate GNRs, the work establishes cyclophane shielding as a general platform for simultaneously controlling dispersibility, electronic structure, and charge transport. By combining steric protection with strain engineering, this approach opens new pathways for integrating graphene nanoribbons into scalable, solution-processed nanoelectronic and quantum devices.
