Emerging Bottom‐Up Strategies for the Synthesis of Graphene Nanoribbons and Related Structures

The solution‐phase synthesis is one of the most promising strategies for the preparation of well‐defined graphene nanoribbons (GNRs) in large scale. To prepare high quality, defect‐free GNRs, cycloaromatization reactions need to be very efficient, proceed without side reaction and mild enough to accommodate the presence of various functional groups. In this Minireview, we present the latest synthetic approaches for the synthesis of GNRs and related structures, including alkyne benzannulation, photochemical cyclodehydrohalogenation, Mallory and Pd‐ and Ni‐catalyzed reactions.     

Magnetism in Nonplanar Zigzag Edge Termini of Graphene Nanoribbons

Graphene nanoribbons (GNRs) and nanographenes synthesized by on-surface reactions using tailor-made molecular precursors offer an ideal playground for a study of magnetism towards nano-spintronics. Although the zigzag edge of GNRs has been known to host magnetism, the underlying metal substrates usually veil the edge-induced Kondo effect. Here, we report the on-surface synthesis of unprecedented, π-extended 7-armchair GNRs using 7-bromo-12-(10-bromoanthracen-9-yl)tetraphene as the precursor. Characterization by scanning tunneling microscopy/spectroscopy revealed unique rearrangement reactions leading to pentagon- or pentagon/heptagon-incorporated, nonplanar zigzag termini, which demonstrated Kondo resonances even on bare Au(111). Density functional theory calculations indicate that the nonplanar structure significantly reduces the interaction between the zigzag terminus and the Au(111) surface, leading to a recovery of the spin localization of the zigzag edge. Such a distortion of planar GNR structures offers a degree of freedom to control the magnetism on metal substrates.     

Upright standing graphene formation on substrates

We propose integrating graphene nanoribbons (GNRs) onto a substrate in an upright position whereby they are chemically bound to the substrate at the basal edge. Extensive ab initio calculations show that both nickel (Ni)- and diamond-supported upright GNRs are feasible for synthesis and are mechanically robust. Moreover, the substrate-supported GNRs display electronic and magnetic properties nearly the same as those of free-standing GNRs. Due to the extremely small footprint of an upright GNR on a substrate, standing GNRs are ideal building blocks for synthesis of subnanometer electronic or spintronic devices. Theoretically, standing GNR-based microchips with field-effect transistor (FET) densities up to 10(13) per cm(2) are achievable.     

On-Surface Synthesis and Spectroscopic Characterization of Laterally Extended Chevron Graphene Nanoribbons

We report the on-surface synthesis and spectroscopic study of laterally extended chevron graphene nanoribbons (GNRs) and compare them with the established chevron GNRs, emphasizing the consistency of bandgap reduction of semiconducting GNRs with increased width. The laterally extended chevron GNRs grown on Au(111) exhibit a bandgap of about 2.2 eV, which is considerably smaller than the values reported for chevron GNRs in similar studies.     

Modulatory Functionalization of Gold Nanorods Using Supramolecular Assemblies

Supramolecular‐assembly‐mediated functionalization of gold nanorods (GNRs) has been developed by reversible phase transfer between water and oils, which offers a facile method for fabricating robust GNRs with surface‐charge tunability. In this regard, trimethylammonium (TMA) GNRs were initially prepared from conventional cetyltrimethylammonium bromide (CTAB) GNRs by means of a ligand‐exchange reaction in the presence of an excess amount of TMA ligands. To further expand their functionality and potential applications, electrostatic assemblies of positively charged TMA‐GNRs with negatively charged oleate ions were prepared. These assemblies (OA‐GNRs) can undergo facile phase transfer from water to hexane. Interestingly, the reversible electrostatic assembly between the TMA and OA ions fabricated onto GNRs can be easily disrupted by treatment with HCl, which removes the OA ions from the GNRs to re‐form the TMA‐GNRs, which can be made soluble in aqueous media again. In addition, OA‐GNRs can be further used for the synthesis of negatively charged GNRs such as 11‐mercaptoundecanoic acid (MUA) GNRs, which are hard to prepare directly from CTAB‐GNRs. This versatile method for phase transfer and functionalization on GNRs is expected to broaden the scope of their applications in sensing, biomedical imaging, photothermal therapies, and drug delivery systems.     

On-surface Synthesis of Graphene Nanoribbons

On-surface synthesis never fails to fascinate chemists by producing new functional polymers which can hardly been prepared via traditional solution chemistry. Among those newly prepared polymers, graphene nanoribbons(GNRs), featured with tunable band gap, have attracted substantial attention because they are considered as promising candidates for next generation carbon-based semiconductors. Here, we summarize the recent advances of GNRs prepared on single crystal surfaces with emphasis on the structural tuning and electronic properties of GNRs. Moreover, critical developments toward the application of GNRs have also been reviewed including the mass fabrication and the performance of GNRs as field effect transistors.     

Heterostructures through Divergent Edge Reconstruction in Nitrogen‐Doped Segmented Graphene Nanoribbons

Atomically precise engineering of defined segments within individual graphene nanoribbons (GNRs) represents a key enabling technology for the development of advanced functional device architectures. Here, the bottom‐up synthesis of chevron GNRs decorated with reactive functional groups derived from 9‐methyl‐9H‐carbazole is reported. Scanning tunneling and non‐contact atomic force microscopy reveal that a thermal activation of GNRs induces the rearrangement of the electron‐rich carbazole into an electron‐deficient phenanthridine. The selective chemical edge‐reconstruction of carbazole‐substituted chevron GNRs represents a practical strategy for the controlled fabrication of spatially defined GNR heterostructures from a single molecular precursor.     

Recent Progress and Challenges in Graphene Nanoribbon Synthesis

Graphene, the thinnest two‐dimensional material in nature, has abundant distinctive properties, such as ultrahigh carrier mobility, superior thermal conductivity, very high surface‐to‐volume ratio, anomalous quantum Hall effect, and so on. Laterally confined, thin, and long strips of graphene, namely, graphene nanoribbons (GNRs), can open the bandgap in the semimetal and give it the potential to replace silicon in future electronics. Great efforts are devoted to achieving high‐quality GNRs with narrow widths and smooth edges. This minireview reports the latest progress in experimental and theoretical studies on GNR synthesis. Different methods of GNR synthesis—unzipping of carbon nanotubes (CNTs), cutting of graphene, and the direct synthesis of GNRs—are discussed, and their advantages and disadvantages are compared in detail. Current challenges and the prospects in this rapidly developing field are also addressed.     

On-Surface Synthesis of One-Dimensional Carbon-Based Nanostructures via C−X and C−H Activation Reactions

The past decades have witnessed the emergence of low-dimensional carbon-based nanostructures owing to their unique properties and various subsequent applications. It is of fundamental importance to explore ways to achieve atomically precise fabrication of these interesting structures. The newly developed on-surface synthesis approach provides an efficient strategy for this challenging issue, demonstrating the potential of atomically precise preparation of low-dimensional nanostructures. Up to now, the formation of various surface nanostructures, especially carbon-based ones, such as graphene nanoribbons (GNRs), kinds of organic (organometallic) chains and films, have been achieved via on-surface synthesis strategy, in which in-depth understanding of the reaction mechanism has also been explored. This review article will provide a general overview on the formation of one-dimensional carbon-based nanostructures via on-surface synthesis method. In this review, only a part of the on-surface chemical reactions (specifically, C−X (X=Cl, Br, I) and C−H activation reactions) under ultra-high vacuum conditions will be covered.     

适体功能化的金纳米棒用于癌症靶向治疗的研究进展

金纳米棒(gold nanorods,GNRs)具有特殊的光学性质、较大的比表面积、出色的光热转换性能、表面易修饰等特点,在药物递送、光疗、生物成像和化学传感等领域应用十分广泛。适体是短的单链DNA或RNA片段,可特异性识别癌细胞或其表面的膜蛋白。近年来,适体功能化的GNRs在癌症靶向治疗领域显示出良好的应用前景。根据GNRs对癌症作用机制的差异,本文从光热疗法、光动力疗法、化疗和联合疗法4个方面总结了适体功能化的GNRs在癌症靶向治疗中的最新进展,并对该领域面临的主要挑战和发展趋势进行了探讨与展望。     

On-Surface Synthesis of NBN-Doped Zigzag-Edged Graphene Nanoribbons

We report the first bottom-up synthesis of NBN-doped zigzag-edged GNRs (NBN-ZGNR1 and NBN-ZGNR2) through surface-assisted polymerization and cyclodehydrogenation based on two U-shaped molecular precursors with an NBN unit preinstalled at the zigzag edge. The resultant zigzag-edge topologies of GNRs are elucidated by high-resolution scanning tunneling microscopy (STM) in combination with noncontact atomic force microscopy (nc-AFM). Scanning tunneling spectroscopy (STS) measurements and density functional theory (DFT) calculations reveal that the electronic structures of NBN-ZGNR1 and NBN-ZGNR2 are significantly different from those of their corresponding pristine fully-carbon-based ZGNRs. Additionally, DFT calculations predict that the electronic structures of NBN-ZGNRs can be further tailored to be gapless and metallic through one-electron oxidation of each NBN unit into the corresponding radical cations. This work reported herein provides a feasible strategy for the synthesis of GNRs with stable zigzag edges yet tunable electronic properties.     

Precisely Tailor the Longitudinal Localized Surface Plasmon Resonance of Gold Nanorods by Mild Oxidation with NaNO2

In this work, we introduce a new method to precisely tailor the longitudinal localized surface plasmon resonance (LLSPR) wavelengths of gold nanorods (GNRs) through the use of NaNO₂ as the oxidant. The effects of the concentrations of NaNO₂, NH₄Br and HCl on the reaction kinetics were investigated separately. To prepare GNRs with desired LLSPR wavelengths, equations were derived and were proved to be able to guide the tailoring of the LLSPR wavelengths through carefully tuning either the amount of NaNO₂ or the reaction time. TEM characterizations performed on two representative sets of GNRs show that the GNRs obtained exhibited shortened lengths but unchanged diameter with good monodispersity. In particular, GNRs with targeted LLSPR at 800 nm, 750 nm, 700 nm and 650 nm were successfully synthesized with relative errors of only 1 %～5 %. This method shall promote more applications of GNRs and may advance the synthesis of other metal nanoparticles.     

On‐Surface Synthesis of NBN‐Doped Zigzag‐Edged Graphene Nanoribbons

We report the first bottom‐up synthesis of NBN‐doped zigzag‐edged GNRs (NBN‐ZGNR1 and NBN‐ZGNR2) through surface‐assisted polymerization and cyclodehydrogenation based on two U‐shaped molecular precursors with an NBN unit preinstalled at the zigzag edge. The resultant zigzag‐edge topologies of GNRs are elucidated by high‐resolution scanning tunneling microscopy (STM) in combination with noncontact atomic force microscopy (nc‐AFM). Scanning tunneling spectroscopy (STS) measurements and density functional theory (DFT) calculations reveal that the electronic structures of NBN‐ZGNR1 and NBN‐ZGNR2 are significantly different from those of their corresponding pristine fully‐carbon‐based ZGNRs. Additionally, DFT calculations predict that the electronic structures of NBN‐ZGNRs can be further tailored to be gapless and metallic through one‐electron oxidation of each NBN unit into the corresponding radical cations. This work reported herein provides a feasible strategy for the synthesis of GNRs with stable zigzag edges yet tunable electronic properties.     

Synthesis of Polybenzoquinolines as Precursors for Nitrogen‐Doped Graphene Nanoribbons

Graphene nanoribbons (GNRs) represent promising materials for the next generation of nanoscale electronics. However, despite substantial progress towards the bottom‐up synthesis of chemically and structurally well‐defined all‐carbon GNRs, strategies for the preparation of their nitrogen‐doped analogs remain at a nascent stage. This scarce literature precedent is surprising given the established use of substitutional doping for tuning the properties of electronic materials. Herein, we report the synthesis of a previously unknown class of polybenzoquinoline‐based materials, which have potential as GNR precursors. Our scalable and facile approach employs few synthetic steps, inexpensive commercial starting materials, and straightforward reaction conditions. Moreover, due to the importance of quinoline derivatives for a variety of applications, the reported findings may hold implications across a diverse range of chemical and physical disciplines.     

Thiolated dextran-coated gold nanorods for photothermal ablation of inflammatory macrophages

Thiolated dextran-coated gold nanorods (DEX-GNRs) were synthesized for targeted delivery to inflammatory macrophages and their photothermal ablation under near-infrared (NIR) light irradiation. Successful synthesis of DEX-GNRs was achieved using thiolated dextran, generated by applying mercaptopropionic acid to transform a hydroxyl group of dextran into a thiol group which has strong binding affinity with surfaces of GNRs. We confirmed both the existence of a thiol group in the functionalized dextran using Ellman's reagent in a thiol group assay and the characteristic band of DEX-GNRs using FT-IR spectrum. Furthermore, a cellular uptake study revealed that dextran showed a superior ability to bind the GNRs surface against macrophages compared to those of PEGylated GNRs with various molecular weights of polyethyleneglycol (PEG). Consequently, an in vitro photothermal irradiation experiment using NIR light indicated that DEX-GNRs exhibited a significant cell-killing efficacy, even with a lower concentration of Au and a low-power light source.     

Graphene Nanoribbons from Tetraphenylethene‐Based Polymeric Precursor: Chemical Synthesis and Application in Thin‐Film Field‐Effect Transistor

Graphene nanoribbons (GNRs) with a non‐zero bandgap are regarded as a promising candidate for the fabrication of electronic devices. In this study, large‐scale solution synthesis of narrow GNRs was firstly achieved by the intramolecular cyclodehydrogenation of kinked tetraphenylethene (TPE) polymer precursors prepared by A₂B₂‐type Suzuki‐Miyaura polymerization. After the cyclization reaction, the nanoribbons have a better conjugation than the twisted polymer precursor, resulting in obvious red shift in UV/vis absorption and photoluminescence (PL) spectra. The efficient formation of conjugated nanoribbons was also investigated by Raman, FTIR spectroscopy, and microscopic studies. Furthermore, such structurally well‐defined GNRs have been successfully developed for top‐gated field‐effect transistor (FET) by directly solution processing. The AFM images show that the prepared‐GNRs thin films form crystalline fibrillar intercalating networks, which can effectively facilitate the charge transport. These FET devices with ion‐gel gate dielectrics exhibit low‐voltage operation (<5 V) with excellent mobility up to 0.41 cm²·V^?1·s^?1 and an on‐off ratio of 3×10⁴, thus opening up new opportunities for flexible GNRs‐based electronic devices.     

Synthesis of dumbbell-shaped Au-Ag core-shell nanorods by seed-mediated growth under alkaline conditions

We report a simple synthesis of Au-Ag core-shell nanorods (NRs) under alkaline conditions (pH 8.0-10.0) from silver and ascorbate ions using gold nanorods (GNRs) as the seeds. The silver ions that are reduced by the ascorbate ions become deposited on the surfaces of the GNRs to form differently dumbbell-shaped Au-Ag core-shell NRs and nanoparticles, depending on the pH and the concentration of silver ions. The longitudinal plasmon absorbance bands of the Au-Ag core-shell NRs are stronger and appear at shorter wavelengths than those for the original GNRs. We confirmed the formation of Au-Ag core-shell NRs by both energy-dispersive X-ray spectrometry and inductively coupled plasma mass spectrometry measurements, which indicate that the 109Ag/197Au ratios are 0.046, 0.085, and 0.097 at pH 8.0, 9.0, and 10.0, respectively. The transmission electron microscopy measurements show that the Au-Ag core-shell NRs are monodispersed (>90%).     

On-surface synthesis of singly and doubly porphyrin-capped graphene nanoribbon segments

On-surface synthesis has emerged as a powerful tool for the construction of large, planar, π-conjugated structures that are not accessible through standard solution chemistry. Among such solid-supported architectures, graphene nanoribbons (GNRs) hold a prime position for their implementation in nanoelectronics due to their manifold outstanding properties. Moreover, using appropriately designed molecular precursors, this approach allows the synthesis of functionalized GNRs, leading to nanostructured hybrids with superior physicochemical properties. Among the potential “partners” for GNRs, porphyrins (Pors) outstand due to their rich chemistry, robustness, and electronic richness, among others. However, the use of such π-conjugated macrocycles for the construction of GNR hybrids is challenging and examples are scarce. Herein, singly and doubly Por-capped GNR segments presenting a commensurate and triply-fused GNR–Por heterojunction are reported. The study of the electronic properties of such hybrid structures by high-resolution scanning tunneling microscopy, scanning tunneling spectroscopy, and DFT calculations reveals a weak hybridization of the electronic states of the GNR segment and the Por moieties despite their high degree of conjugation.

Singly and doubly porphyrin-capped graphene nanoribbon segments are reported and their electronic properties are studied by high-resolution scanning tunneling microscopy and spectroscopy, and DFT calculations.     

环糊精与表面活性剂主客体作用诱导的金纳米棒可控自组装

The self-assembly of colloidal nanocrystals has emerged as a powerful strategy for the bottom-up fabrication of functional materials and nanodevices. Recently, the self-assembly of gold nanorods (GNRs) has attracted significant attention because of their unique plasmonic properties, but the realization of their adjustable self-assembly of GNRs through facile and effective approaches remains challenging. In this work, the controllable self-assembly of GNRs in aqueous solution was realized through the host-guest interactions of cyclodextrins (CDs) and the cetyltrimethylammonium bromide (CTAB) molecules adsorbed on the surface of the GNRs. The self-assembly of GNRs was readily achieved by the addition of aqueous α-CD solutions with varied concentrations into aqueous dispersions of CTAB-stabilized GNRs. At a relatively low α-CD concentration, slow aggregation of the GNRs occurred, resulting in their side-by-side assembly. This was revealed by the blue shift of the longitudinal surface plasmon resonance (LSPR) band in the absorption spectra and confirmed by transmission electron microscopy (TEM) observations. On the other hand, when a higher concentration of α-CD was added, fast aggregation of the GNRs occurred, resulting in their end-to-end assembly. This was revealed by the red shift in the LSPR band together with the TEM observations. If β-CD was employed instead of α-CD, the self-assembly of GNRs could also be induced, although a relatively higher concentration of β-CD was required to achieve the extent of aggregation similar to that induced by α-CD, indicating that the supramolecular host–guest interaction between CDs and the surfactant CTAB was crucial to the directed self-assembly of GNRs. Furthermore, the α-CD-induced assembly was inhibited on addition of excess CTAB, confirming that the supramolecular interaction of α-CD and CTAB played a key role in directing the self-assembly of the GNRs. Based on these experimental results, a possible mechanism for the α-CD-induced self-assembly of GNRs was proposed as follows: at a lower α-CD concentration, the gradual formation of the host-guest inclusion complex α-CD/CTAB led to the partial replacement of the highly charged CTAB bilayers adsorbed on the GNRs by the less charged complex, which resulted in a slow side-by-side assembly of the GNRs; at a higher α-CD concentration, the CTAB bilayers were quickly replaced by the α-CD/CTAB complex, and the CTAB molecules adsorbed at both ends of the GNRs were almost completely replaced, resulting in a fast end-to-end assembly of the GNRs. Additionally, on the basis of the hydrolysis of α-cyclodextrin catalyzed by α-amylase, the self-assembly of GNRs directed by the host-guest interaction could be used to realize the feasible detection of α-amylase in solutions. This self-assembly strategy mediated by the host-guest interaction may be extendable to other colloidal systems involving surfactants adsorbed on the surface of nanoparticles, and may open new avenues for the controllable self-assembly of non-spherical nanoparticles.     

Degradation of Structurally Defined Graphene Nanoribbons by Myeloperoxidase and the Photo-Fenton Reaction

As an emerging member of the graphene family, structurally defined graphene nanoribbons (GNRs) have shown promising applications in various fields. The evaluation of the degradability of GNRs is particularly important for assessing the persistence level and risk of these materials in living organisms and the environment. However, there is a void in the study of the degradation of GNRs. Here, we report the degradation behavior of GNRs in the presence of human myeloperoxidase (hMPO) or treated with the photo-Fenton (PF) reaction. With the assistance of potassium hydroxide or imidazole, which facilitates the dispersion of GNRs in the aqueous solution, GNRs underwent only partial degradation after 25-hour incubation with hMPO, while, the PF reaction degraded GNRs almost completely after 120 hours. These results indicate that structurally precise GNRs can be efficiently degraded under suitable conditions, providing more opportunities for future applications in different fields.