Large π-Extended and Curved Carbon Nanorings as Carbon Nanotube Segments.

ConspectusDesigning and synthesizing topologically unique molecules is a long-term challenge for synthetic chemists. Classical polycyclic aromatic hydrocarbons (PAHs) are a large group of π-conjugated planar organic compounds with rich photophysical and electronic properties, while nonplanar/curved PAHs have different molecular orbital arrangements and demonstrate unique properties. The chemistry of curved aromatic molecules has been of significant interest to explore the relationship between π conjugation and molecular geometry, which offers an attractive combination of fundamental problems, potential applications, and aesthetic appeal. Remarkable advances have been made in the last few decades during the discovery of novel curved aromatic molecules, including corannulenes, fullerenes, and carbon nanotubes (CNTs). Especially, there has been increasing interest in making single-chirality CNTs and their curved molecular components (known as finite segments of CNTs) with a fixed geometry. The most representative examples of such organic molecules are cycloparaphenylenes (CPPs) and related carbon nanorings, which possess cylindrical topologies and nanoscale conjugated segments similar to CNTs. CPPs, as the shortest cross-section and the simplest structure of armchair CNTs, have been synthetically accessible since 2008. Recent years have witnessed breakthroughs and rapid development in the synthesis of CPP-based nanorings as well as their derived molecules. In these molecules, the distortion from aromatic planarity can induce radially oriented π systems and further affect their electronic, optical, self-assembly, and charge-transport characteristics. These unique and interesting carbon nanorings are potentially useful in a variety of optoelectronic and biomedical materials. It is well-known that extension of the π-conjugated system facilitates the delocalization of π electrons and the redistribution of electronic clouds, leading to rich diversification of physical properties in the fields of electronics, optics, and supramolecular chemistry. Therefore, the precise design and controllable synthesis of carbon nanorings with large π conjugation will promote important advances in synthetic chemistry. To date, a number of π-extended carbon nanorings have been reported, and they exhibit novel physicochemical properties resulting from their fascinating topologies and structures. However, challenges still remain in the synthesis of π-extended carbon nanorings and their structural analogues and exploration of their unique properties.In this Account, we give a brief overview of our efforts to synthesize large π-extended carbon nanorings using different strategies and explore their novel applications. In 2013 we started our research on the synthesis of carbon nanorings with large π-conjugated structures. This research project has led to (i) the successful preparation of a series of carbon nanorings with inserted PAHs, especially with various nanographenes inserted, such as hexa-peri-hexabenzocoronene; (ii) the design and synthesis of a series of carbon nanorings consisting solely of PAHs; and (iii) the initial synthesis of π-extended carbon-nanoring-based polymers as the long polymeric segments of CNTs, in which macrocyclic CPPs as the basic repeating blocks were covalently coupled together. Herein we describe in detail how these challenging π-extended carbon nanorings were synthesized, and their interesting physical properties are discussed.

Synthesis of Giant π-Extended Molecular Macrocyclic Rings as Finite Models of Carbon Nanotubes Displaying Enriched Size-Dependent Physical Properties.

Bottom-up synthesis of π-extended macrocyclic carbon rings is promising for constructing length- and diameter-specific carbon nanotubes (CNTs). However, it is still a great challenge to realize size-controllable giant carbon macrocycles. Herein, a tunable synthesis of curved nanographene-based giant π-extended macrocyclic rings (CHBC[n]s; n=8, 6, 4), as finite models of armchair CNTs, is reported. Among them, CHBC[8] contains 336 all-carbon atoms and is the largest cyclic conjugated molecular CNT segment ever reported. CHBC[n]s were systematically characterized by various spectroscopic methods and applied in photoelectrochemical cells for the first time. This revealed that the proton chemical shifts, fluorescence, and electronic and photoelectrical properties of CHBC[n]s are highly dependent on the macrocycle diameter. The tunable bottom-up synthesis of giant macrocyclic rings could pave the way towards large π-extended diameter- and chirality-specific CNT segments.

Selective Synthesis of Conjugated Chiral Macrocycles: Sidewall Segments of (-)/(+)-(12,4) Carbon Nanotubes with Strong Circularly Polarized Luminescence.

Carbon nanotubes (CNTs) have unusual physical properties that are valuable for nanotechnology and electronics, but the chemical synthesis of chirality- and diameter-specific CNTs and π-conjugated CNT segments is still a great challenge. Reported here are the selective syntheses, isolations, characterizations, and photophysical properties of two novel chiral conjugated macrocycles ([4]cyclo-2,6-anthracene; [4]CAn2,6 ), as (-)/(+)-(12,4) carbon nanotube segments. These conjugated macrocyclic molecules were obtained using a bottom-up assembly approach and subsequent reductive elimination reaction. The hoop-shaped molecules can be directly viewed by a STM technique. In addition, chiral enantiomers with (-)/(+) helicity of the [4]CAn2,6 were successfully isolated by HPLC. The new tubular CNT segments exhibit large absorption and photoluminescence redshifts compared to the monomer unit. The carbon enantiomers are also observed to show strong circularly polarized luminescence (glum ≈0.1). The results reported here expand the scope of materials design for bottom-up synthesis of chiral macrocycles and enrich existing knowledge of their optoelectronic properties.

Kinetic Control over Morphology of Nanoporous Graphene on Surface.

On-surface synthesis of high-quality nanoporous graphene (NPG) for application in nanotechnology and nanodevices remains challenging. Rational design of molecular precursors and proper kinetic control over the reaction process are the two key factors to tune the synthesis. Herein, we report a detailed study of the coupling reactions of a planar halogen-substituted nanographene molecular precursor, hexaiodo-peri-hexabenzocoronene (I6 -HBC), on the Au(111) surface in the synthesis of NPG. The influence of three basic kinetic processes - molecular adsorption, migration, and coupling - on the synthesis was investigated. The results show that the HBC molecules deposited at low temperature predominantly desorb from the Au(111) surface during the annealing process, whereas depositing the precursor molecules onto a hot surface (700 K) can lead to the formation of NPG. However, at such a high surface temperature, simultaneous intermolecular dehydrogenative coupling between HBC monomers can hinder the ordered growth of NPG through Ullmann coupling. Moreover, the deposition rate of the precursors greatly influences the growth morphology of the NPG nanostructures.

Photoconductive Curved-Nanographene/Fullerene Supramolecular Heterojunctions.

This study presents synthesis and characterizations of two novel curved nanographenes that strongly bind with fullerene C60 to form photoconductive heterojunctions. Films of the self-assembled curved nanographene/fullerene complexes, which served as the photoconductive layer, generated a significant photocurrent under light irradiation. Gram-scale quantities of these curved nanographenes (TCR and HCR) as the "crown" sidewalls can be incorporated into a carbon nanoring to form molecular crowns, and the molecular structure of C60 @TCR is determined by single-crystal X-ray diffraction. The UV/Vis absorption and emission spectra, and theoretical studies revealed their unique structural features and photophysical properties. Time-resolved spectroscopic results clearly suggest fast photoinduced electron transfer process in the supramolecular heterojunctions.

A Three-Dimensional Capsule-like Carbon Nanocage as a Segment Model of Capped Zigzag [12,0] Carbon Nanotubes: Synthesis, Characterization, and Complexation with C70.

Herein we report the synthesis and photophysical and supramolecular properties of a novel three-dimensional capsule-like hexa-peri-hexabenzocoronene (HBC)-containing carbon nanocage, tripodal-[2]HBC, which is the first synthetic model of capped zigzag [12,0] carbon nanotubes (CNTs). Tripodal-[2]HBC was synthesized by the palladium-catalyzed coupling of triboryl hexabenzocoronene and L-shaped cyclohexane units, followed by nickel-mediated C-Br/C-Br coupling and subsequent aromatization of the cyclohexane moieties. The physical properties of tripodal-[2]HBC and its supramolecular host-guest interaction with C70 were further studied by UV/Vis and fluorescence spectroscopy. Theoretical calculations revealed that the strain energy of tripodal-[2]HBC was as high as 55.2 kcal mol-1 .

Reversible mechanochromic luminescence at room temperature in cationic platinum(II) terpyridyl complexes.

Reversible mechanochromic luminescence in cationic platinum(II) terpyridyl complexes is described. The complexes [Pt(Nttpy)Cl]X2 (Nttpy = 4'-(p-nicotinamide-N-methylphenyl)-2,2':6',2″-terpyridine, X = PF6 (1), SbF6 (2), Cl (3), ClO4 (4), OTf (5), BF4 (6)) exhibit different colors under ambient light in the solid state, going from red to orange to yellow. All of these complexes are brightly luminescent at both room temperature and 77 K. Upon gentle grinding, the yellow complexes (4-6) turn orange and exhibit bright red luminescence. The red luminescence can be changed back to yellow by the addition of a few drops of acetonitrile to the sample. Crystallographic studies of the yellow and red forms of complex 5 suggest that the mechanochromic response is likely the result of a change in intermolecular Pt···Pt distances upon grinding.

Cobalt porphyrin electrode films for electrocatalytic water oxidation.

Catalysts play very important roles in artificial photosynthesis for solar energy conversion. In this present study, two water-insoluble cobalt porphyrin complexes, cobalt(II) meso-tetraphenylporphyrin (CoP-1) and cobalt(II) 5,10,15,20-tetrakis-(4-bromophenyl)porphyrin (CoP-2), were synthesized and coated as thin films on the FTO working electrode. The films showed good activities for electrocatalytic water oxidation in aqueous solutions at pH 9.2. The Faradaic efficiencies of both films approached to ~100%, measured using a fluorescence-based oxygen sensor. The turnover frequencies were close to 0.50 s(−1) and 0.40 s(−1) for CoP-1 and CoP-2, respectively, under an applied anodic potential of 1.3 V (vs. Ag/AgCl) at pH 9.2. Importantly, no cobalt oxide particles were observed on the working electrode after catalysis. The stability of the catalyst films was further evaluated by UV-vis spectroscopy, inhibition measurements, mass spectrometry, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The pH dependence of water oxidation on CoP-1 and CoP-2 suggested a proton-coupled electron transfer (PCET) mechanism. The catalyst films could be recycled and showed almost unchanged catalytic activities when they were reused in new electrocatalytic studies of water oxidation.

Nitrogen-doped biomass-derived carbon dots for fluorescence determination of sunset yellow.

Sunset Yellow (SY) is a widely used food coloring in the food industry. However, exceeding the allowable limit of this dye poses a significant threat to human health. To address this issue, we developed Lycium ruthenicum-derived nitrogen-doped carbon dots (N-CDs) with a stable blue fluorescence through hydrothermal treatment for SY determination. The quantum yield (QY) of these N-CDs was found to be up to 10.63%. Physical characterization of N-CDs was performed using various spectroscopic techniques to confirm their excellent photostability and non-toxic properties. Furthermore, the presence of SY had a substantial quenching effect on the fluorescence intensity (F0/F) of the N-CDs. Leveraging this observation, we developed a fluorescent sensor for the determination of SY in the concentration range of 0.05 to 35.0 µM, with a limit of detection (LOD, 3σ/K) of 17 nM. The excellent fluorescent sensor also showed satisfactory results in the practical drink samples. Moreover, the stability and cytotoxicity of N-CDs as a fluorescent probe were studied. Finally, the N-CDs were applied to cell imaging using A549 cells.

Large-Scale Integration of the Ion-Reinforced Phytic Acid Layer Stabilizing Magnesium Metal Anode.

Rechargeable magnesium batteries (RMBs) have garnered significant attention for their potential in large-scale energy storage applications. However, the commercial development of RMBs has been severely hampered by the rapid failure of large-sized Mg metal anodes, especially under fast and deep cycling conditions. Herein, a concept proof involving a large-scale ion-reinforced phytic acid (PA) layer (100 cm × 7.5 cm) with an excellent water-oxygen tolerance, high Mg2+ conductivity, and favorable electrochemical stability is proposed to enable rapid and uniform plating/stripping of Mg metal anode. Guided by even distributions of Mg2+ flux and electric field, the as-prepared large-sized PA-Al@Mg electrode (5.8 cm × 4.5 cm) exhibits no perforation and uniform Mg plating/stripping after cycling. Consequently, an ultralong lifespan (2400 h at 3 mA cm-2 with 1 mAh cm-2) and high current tolerance (300 h at 9 mA cm-2 with 1 mAh cm-2) of the symmetric cell using the PA-Al@Mg anode could be achieved. Notably, the PA-Al@Mg//Mo6S8 full cell demonstrates exceptional stability, operating for 8000 cycles at 5 C with a capacity retention of 99.8%, surpassing that of bare Mg (3000 cycles, 74.7%). Moreover, a large-sized PA-Al@Mg anode successfully contributes to the stable pouch cell (200 and 750 cycles at 0.1 and 1 C), further confirming its significant potential for practical utilization. This work provides valuable theoretical insights and technological support for the practical implementation of RMBs.

Facile deposition of nanostructured cobalt oxide catalysts from molecular cobaloximes for efficient water oxidation.

Cobaloximes are usually used as molecular hydrogen evolution reaction (HER) catalysts. Herein we report for the first time the use of molecular cobaloximes as catalyst precursors for water oxidation when anodic potentials were applied. Highly active thin catalyst films were deposited at +1.5 V and +1.1 V (vs. Ag/AgCl) in 0.1 M borate buffer solution at pH = 9.2 containing 1 mM cobaloximes. Four catalyst films (CoOx-1-CoOx-4) were synthesized from four different cobaloximes. The current densities of CoOx-1 were up to ~5.5 mA cm(-2) and ~2.6 mA cm(-2) when the applied potentials were +1.5 V and +1.1 V, respectively, which were higher than the current densities of CoOx-2, CoOx-3 and CoOx-4 under the same conditions. Scanning electron microscopy (SEM) images reveal that the nanometer-sized particles of CoOx-1 possibly contribute to its high activity while the other three catalysts have micrometer-sized amorphous materials on the surface of FTO. X-ray photoelectron spectroscopy (XPS) data displayed the valence state of the cobalt element as Co(ii) or Co(iii) oxide species. The morphological stability of the CoOx-1 catalyst was further studied using SEM.

3D artificial sebocyte glands from inertial focusing effect for facile and flexible analysis of light damage and drug screening.

The sebaceous gland is a neuro-immuno-endocrine organ responsible for maintaining regular skin functions. Overdose exposure of UV and visible light (e.g., blue light) can cause sebocyte gland function disorders or even different diseases (e.g., chronic actinic dermatitis). Studying the mechanism of light-induced damage in sebaceous glands has been challenging, since ex vivo culture of sebaceous glands is difficult due to its short life in culture medium. To address this issue, a versatile 3D artificial sebocyte gland model was established using the inertial focusing effect for studying the impact of light damage and screening potential drugs. The artificial sebocyte gland exhibited specific biological function and structure similar to natural sebocyte glands. Using this artificial sebocyte gland, the interactions between the artificial organ and blue light or UV were studied. The results indicated that UV and blue light upregulated lipid secretion and downregulated cell viability within the sebocytes. Light damage intensified oxidative stress and promoted pro-inflammation cytokines (i.e., IL-1ß and TNF-α) production in the artificial sebocytes. Additionally, the therapeutic effects of cannabidiol, a clinically tested drug for treating acne, was also indicated on restoring light damaged sebaceous gland functions. These results indicate that the 3D artificial sebocyte gland could be a versatile, fast, and low-cost platform for skincare studies or drug screening.

Distinct armchair and zigzag charge transport through single polycyclic aromatics.

In aromatic systems with large π-conjugated structures, armchair and zigzag configurations can affect each material's electronic properties, determining their performance and generating certain quantum effects. Here, we explore the intrinsic effect of armchair and zigzag pathways on charge transport through single hexabenzocoronene molecules. Theoretical calculations and systematic experimental results from static carbon-based single-molecule junctions and dynamic scanning tunneling microscope break junctions show that charge carriers are preferentially transported along the hexabenzocoronene armchair pathway, and thus, the corresponding current through this pathway is approximately one order of magnitude higher than that through the zigzag pathway. In addition, the molecule with the zigzag pathway has a smaller energy gap. In combination with its lower off-state conductance, it shows a better field-effect performance because of its higher on-off ratio in electrical measurements. This study on charge transport pathways offers a useful perspective for understanding the electronic properties of π-conjugated systems and realizing high-performance molecular nanocircuits toward practical applications.

Overexpression of interleukin-10 in engineered macrophages protects endothelial cells against LPS-induced injury in vitro.

Endothelial dysfunction is a primary pathophysiological change in sepsis. Macrophages are known to interact with vascular endothelial cells during the development of sepsis. Recently, drug delivery based on engineered macrophages was reported as an alternative approach for the management of diseases. Interleukin-10 (IL10) is a well-known anti-inflammatory cytokine, which reduces inflammation and inhibits dysfunction of endothelial cells caused by sepsis. It is currently poorly understood whether genetically modified macrophages with overexpression of IL10 are able to restore endothelial integrity and function at the cellular level. In this study, we used lentiviral vectors to construct RAW264.7 macrophages engineered to overexpress IL10 (IL10-eM) and investigated the effects of the IL10-eM supernatant on LPS-induced endothelial dysfunction using a noncontact coculture system. We found that cotreatment with IL10-eM supernatant significantly attenuates the effects of LPS-induced dysfunction of endothelial cells, including endothelial inflammatory response, endothelial permeability, and apoptosis. In addition, we discovered that LPS-induced downregulation of VE-cadherin and high production of reactive oxygen species were significantly attenuated upon IL10-eM exposure. Furthermore, upregulation of IL6, TNFα, and Bax was decreased after treatment of cells with IL10-eM supernatant. These results demonstrated that supernatant from engineered macrophages genetically modified with IL10 can effectively protect endothelial cells against LPS-induced dysfunction in vitro, suggesting that exosomes from such engineered macrophages may have therapeutic effects against sepsis.

Two-dimensional conductive phthalocyanine-based metal-organic frameworks for electrochemical nitrite sensing.

2D nickel phthalocyanine based MOFs (NiPc-MOFs) with excellent conductivity were synthesized through a solvothermal approach. Benefiting from excellent conductivity and a large surface area, 2D NiPc-MOF nanosheets present excellent electrocatalytic activity for nitrite sensing, with an ultra-wide linear concentration from 0.01 mM to 11 500 mM and a low detection limit of 2.3 µM, better than most reported electrochemical nitrite sensors. Significantly, this work reports the synthesis of 2D conductive NiPc-MOFs and develops them as electrochemical biosensors for non-enzymatic nitrite determination for the first time.

On-surface synthesis of planar acenes via regioselective aryl-aryl coupling.

The reaction of 2,2'-dibromo-biphenyl on a Ag(111) surface leads to the formation of planar acenes with a high-regioselectivity rather than nonplanar saddle-shaped tetraphenylene as the typical product in solution chemistry. The regioselective aryl-aryl coupling reaction is attributed to the hydrogen repulsion between the reactants on the confined two-dimensional surface.

From Planar Macrocycle to Cylindrical Molecule: Synthesis and Properties of a Phenanthrene-Based Coronal Nanohoop as a Segment of [6,6]Carbon Nanotube.

Herein, we explore phenanthrene as the building block to synthesize a hoop-shaped [6,6]carbon nanotube segment from a planar macocycle via a Diels-Alder reaction. The phenanthrene-based coronal nanohoop 7 was fully characterized by HR-MS, NMR, and other spectroscopies. In addition, its photophysical properties and the supramolecular interactions between 7 and fullerene C60 were investigated. This present work suggests an easily accessible Diels-Alder reaction strategy to synthesize cylindrical nanohoops.

Harnessing the layer-by-layer assembly technique to design biomaterials vaccines for immune modulation in translational applications.

The existence of challenging diseases such as cancers, HIV and Zika requires developing new vaccines that can generate tunable and robust immune responses against the diseases. Biomaterials-based techniques have been broadly explored for designing vaccines that can produce controllable and potent immunity. Among the existing biomaterials-based strategies, the layer-by-layer (LbL) assembly technique is remarkably attractive in vaccine design due to its unique features such as programmed and versatile cargo loading, cargo protection, co-delivery, juxtaposing of immune signals, etc. In this work, we reviewed the existing LbL-based vaccine design techniques for translational applications. Specifically, we discussed nanovaccines constructed by coating polyelectrolyte multilayers (PEMs) on nanoparticles, microcapsule vaccines assembled from PEMs, polyplex/complex vaccines condensed from charged materials and microneedle vaccines deposited with PEMs, highlighting the employment of these techniques to promote immunity against diseases ranging from cancers to infectious and autoimmune diseases (i.e., HIV, influenza, multiple sclerosis, etc.). Additionally, the review specifically emphasized using LbL-based vaccine technologies for tuning the cellular and molecular pathways, demonstrating the unique advantages presented by these vaccination strategies. These studies showed the versatility and potency of using LbL-based techniques for designing the next generation of biomaterials vaccines for translational purposes.

Facile three-step synthesis and photophysical properties of [8]-, [9]-, and [12]cyclo-1,4-naphthalene nanorings via platinum-mediated reductive elimination.

Herein we report a facile three-step synthesis of [8]-, [9]-, and [12]cyclo-1,4-naphthalene nanorings as the conjugated segments of carbon nanotubes. The nanorings were created via a platinum-mediated assembly of 1,4-naphthalene-based units and subsequent reductive elimination in the presence of triphenylphosphine. This present platinum-mediated approach is attractive because of its simple three-step process to produce the targeted nanorings in a high overall yield. In addition, their photophysical properties were studied using UV-vis spectroscopy and photoluminescence (PL) spectroscopy, which further revealed their unique size-dependent properties.

Pyrolyzed cobalt porphyrin-based conjugated mesoporous polymers as bifunctional catalysts for hydrogen production and oxygen evolution in water.

In this present study, a series of cobalt porphyrin-based conjugated mesoporous polymers (CoP-nph-CMP, n = 2, 3, 4) were fabricated as catalyst precursors to generate bifunctional catalysts via pyrolysis (CoP-nph-CMP-800, n = 2, 3, 4) for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Among these catalysts, CoP-2ph-CMP-800 exhibited the best catalytic activity with quite a low overpotential for both the OER (η = 370 mV for 10 mA cm-2) and the HER (η = 360 mV for 10 mA cm-2). Moreover, their excellent bifunctional catalytic performance was also explored in the overall water splitting test (η = 760 mV for 10 mA cm-2).