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Conjugation of nanographenes (NGs) with electro-active molecules can establish donor-acceptor π-systems in which the former generally serve as the electron-donating moieties due to their electronic-rich nature. In contrast, here we report a series of reversed donor-acceptor structures are obtained by C–N coupling of electron-deficient perchlorinated NGs with electron-rich anilines. Selective amination at the vertexes of the NGs is unambiguously shown through X-ray crystallography. By varying the donating ability of the anilino groups, the optical and assembly properties of donor-acceptor NGs can be finely modulated. The electron-deficient concave core of the resulting conjugates can host electron-rich guest molecules by intermolecular donor-acceptor interactions and gives rise to charge-transfer supramolecular architectures. Nanographenes in donor-acceptor π-systems generally serve as electron-donating moieties but the reversed structures are hardly reported. Here, the authors present a facile synthetic protocol towards reversed donor-acceptor nanographenes by amination and demonstrate fine property tuning by varying the donating ability of the aniline groups.

Electrets are dielectric materials that have a quasi-permanent dipole polarization. A single-molecule electret is a long-sought-after nanoscale component because it can lead to miniaturized non-volatile memory storage devices. The signature of a single-molecule electret is the switching between two electric dipole states by an external electric field. The existence of these electrets has remained controversial because of the poor electric dipole stability in single molecules. Here we report the observation of a gate-controlled switching between two electronic states in Gd@C82. The encapsulated Gd atom forms a charged centre that sets up two single-electron transport channels. A gate voltage of ±11 V (corresponding to a coercive field of ~50 mV Å–1) switches the system between the two transport channels with a ferroelectricity-like hysteresis loop. Using density functional theory, we assign the two states to two different permanent electrical dipole orientations generated from the Gd atom being trapped at two different sites inside the C82 cage. The two dipole states are separated by a transition energy barrier of 11 meV. The conductance switching is then attributed to the electric-field-driven reorientation of the individual dipole, as the coercive field provides the necessary energy to overcome the transition barrier.A Gd@C82 molecule shows electric polarization switching behaviour under a gate bias voltage, thus demonstrating a single-molecule electret device.

Chemical functionalization is one of the most powerful and widely used strategies to control the properties of nanomaterials, particularly in the field of graphene. However, the ill-defined structure of the present functionalized graphene inhibits atomically precise structural characterization and structure-correlated property modulation. Here we present a general edge chlorination protocol for atomically precise functionalization of nanographenes at different scales from 1.2 to 3.4 nm and its application in graphene nanoribbons. The well-defined edge chlorination is unambiguously confirmed by X-ray single-crystal analysis, which also discloses the characteristic non-planar molecular shape and detailed bond lengths of chlorinated nanographenes. Chlorinated nanographenes and graphene nanoribbons manifest enhanced solution processability associated with decreases in the optical band gap and frontier molecular orbital energy levels, exemplifying the structure-correlated property modulation by precise edge chlorination. Chemical functionalization of graphene is a useful method for modulating its properties, although this is limited by a lack of control and resulting in poorly defined structures. Here the authors report the atomically precise chlorination of nanographenes and apply the methods to graphene nanoribbons.

Full-carbon electronics at the scale of several angstroms is an expeimental challenge, which could be overcome by exploiting the versatility of carbon allotropes. Here, we investigate charge transport through graphene/single-fullerene/graphene hybrid junctions using a single-molecule manipulation technique. Such sub-nanoscale electronic junctions can be tuned by band gap engineering as exemplified by various pristine fullerenes such as C 60 , C 70 , C 76 and C 90 . In addition, we demonstrate further control of charge transport by breaking the conjugation of their π systems which lowers their conductance, and via heteroatom doping of fullerene, which introduces transport resonances and increase their conductance. Supported by our combined density functional theory (DFT) calculations, a promising future of tunable full-carbon electronics based on numerous sub-nanoscale fullerenes in the large family of carbon allotropes is anticipated. All-carbon electronics holds promise beyond the conventional silicon-based electronics, but it remains challenging to manufacture them with well-defined structures thus tunability. Tan et al. control charge transport in single-molecule junctions using different fullerenes between graphene electrodes.

Bilayer graphene consists of two stacked graphene layers bound together by van der Waals interaction. As the molecular analog of bilayer graphene, molecular bilayer graphene (MBLG) can offer useful insights into the structural and functional properties of bilayer graphene. However, synthesis of MBLG, which requires discrete assembly of two graphene fragments, has proved to be challenging. Here, we show the synthesis and characterization of two structurally well-defined MBLGs, both consisting of two π−π stacked nanographene sheets. We find they have excellent stability against variation of concentration, temperature and solvents. The MBLGs show sharp absorption and emission peaks, and further time-resolved spectroscopic studies reveal drastically different lifetimes for the bright and dark Davydov states in these MBLGs. Molecular bilayer graphene — a discrete assembly of two stacked graphene fragments — is challenging to produce in pure form. Here, the authors are able to synthesize and characterize stable molecular bilayer graphenes by the π−π stacking of two identical, well-defined nanographene sheets.

Although water‐soluble graphene quantum dots (GQDs) have shown various promising bio‐applications due to their intriguing optical and chemical properties, the large heterogeneity in compositions, sizes, and shapes of these GQDs hampers the better understanding of their structure‐properties correlation and further uses in terms of large‐scale manufacturing practices and safety concerns. It is shown here that a water‐soluble atomically‐precise GQD (WAGQD‐C96) is synthesized and exhibits a deep‐red emission and excellent sonodynamic sensitization. By decorating sterically hindered water‐soluble functional groups, WAGQD‐C96 can be monodispersed in water without further aggregation. The deep‐red emission of WAGQD‐C96 facilitates the tracking of its bio‐process, showing a good cell‐uptake and long‐time retention in tumor tissue. Compared to traditional molecular sonosensitizers, WAGQD‐C96 generates superior reactive oxygen species and demonstrates excellent tumor inhibition potency as an anti‐cancer sonosensitizer in in vivo studies. A good biosafety of WAGQD‐C96 is validated in both in vitro and in vivo assays. A water‐soluble atomically‐precise graphene quantum dot (WAGQD) with deep‐red emission is synthesized and shows a superior sensitizing potency for cancer sonodynamic therapy. The general synthetic strategy will enable the synthesis of WAGQDs with different sizes, edges, and tailored properties for further bio‐applications.

Quintulene, a non-graphitic cycloarene with fivefold symmetry, has remained synthetically elusive due to its high molecular strain originating from its curved structure. Here we report the construction of extended quintulene, which was unambiguously characterized by mass and NMR spectroscopy. The extended quintulene represents a naturally curved nanocarbon based on its conical molecular geometry. It undergoes dimerization in solution via π−π stacking to form a metastable, but isolable bilayer complex. Thermodynamic and kinetic characterization reveals the dimerization process as entropy-driven and following second-order kinetics with a high activation energy. These findings provide a deeper understanding of the assembly of conical nanocarbons. Comparison of optical properties of monomer and dimer points toward a H-type interlayer coupling in the dimer. Quintulene, a quintuple non-graphitic cycloarene, is challenging to synthesize. Here, the authors synthesize and characterize the cone-shaped extended quintulene and its bilayer dimer, and disclose its dimerization as an entropy-driven, second-order reaction with a substantial activation energy.

One- and two-dimensional (1D-2D) heterostructures have drawn growing interest due to their appealing optoelectronic and catalytic properties. Controlling the band alignment of 1D-2D heterostructures is crucial for their large-scale applications, but remains challenging to achieve experimentally. Here, we report a strategy for the atomically precise fabrication of 1D graphene nanoribbon (GNR) homojunctions and a variety of 1D-GNRs/2D-CuSe vertical heterostructures on Cu(111) substrate. By combining scanning tunneling microscopy, non-contact atomic force microscopy characterizations and density functional theory calculations, the entire preparative process is fully visualized. The GNR homojunctions, which bridge the Cu(111) substrate and the semiconducting CuSe monolayer, show a p-n junction characteristic. The hybrid heterostructures display various band alignments, achieved by varying the width and edge topologies of the GNRs, as well as controlling two different semiconducting phases of the CuSe monolayer. This work offers a promising method to precisely synthesize 1D/2D heterostructures with diverse band alignments for applications in high-performance nanodevices. Mixed-dimensional 1D-2D heterostructures hold promise for catalytic and optoelectronic applications, but the control of their electronic band structure remains challenging. Here, the authors report the fabrication of 1D-graphene nanoribbon/2D-CuSe heterojunctions with tunable band alignment by varying the geometry and phase of the materials.

Artificial electronic kagome lattices may emerge from electronic potential landscapes using customized structures with exotic supersymmetries, benefiting from the confinement of Shockley surface-state electrons on coinage metals, which offers a flexible approach to realizing intriguing quantum phases of matter that are highly desired but scarce in available kagome materials. Here, we devise a general strategy to construct varieties of electronic kagome lattices by utilizing the on-surface synthesis of halogen hydrogen-bonded organic frameworks (XHOFs). As a proof of concept, we demonstrate three XHOFs on Ag(111) and Au(111) surfaces, which correspondingly deliver regular, breathing, and chiral breathing diatomic-kagome lattices with patterned potential landscapes, showing evident topological edge states at the interfaces. The combination of scanning tunnelling microscopy and noncontact atomic force microscopy, complemented by density functional theory and tight-binding calculations, directly substantiates our method as a reliable and effective way to achieve electronic kagome lattices for engineering quantum states. By utilizing the templating effect of a halogen hydrogen-bonded organic framework, the authors show that the Shockley surface states of coinage metals can be patterned into artificial kagome lattices with high tunability.

The most stable fullerenes obey the isolated-pentagon rule (IPR): hexagons of carbon atoms entirely surround pentagons to minimize strain. Recently, some examples of fused-pentagon fullerenes have been reported and this Review summarizes current work to stabilize non-IPR fullerenes. The isolated pentagon rule (IPR) is now widely accepted as a general rule for determining the stability of all-carbon fullerene cages composed of hexagons and pentagons. Fullerenes that violate this rule have been deemed too reactive to be synthesized. The stabilization of non-IPR endohedral fullerenes depends on charge transfer from the encapsulated metal clusters (endoclusters) to fullerene cages, the electronic properties of empty all-carbon cages, the matching size and geometries of fullerene and endocluster, as well as the strong coordination of the metal ions to fused pentagons. The stability of non-IPR exohedral fullerenes can be rationalized primarily by both the 'strain-relief' and 'local-aromaticity' principles. This Review focuses on recent work on stabilization of non-IPR fullerenes, including theoretical and empirical principles, experimental methods, and molecular structures of fused-pentagon fullerenes characterized so far. The special chemical properties of non-IPR fullerenes that distinguish them from IPR-satisfying ones are also emphasized.