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1.
J Am Chem Soc ; 142(42): 17881-17886, 2020 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-33021787

RESUMO

Bottom-up-synthesized graphene nanoribbons (GNRs) with excellent electronic properties are promising materials for energy storage systems. Herein, we report bottom-up-synthesized GNR films employed as electrode materials for micro-supercapacitors (MSCs). The micro-device delivers an excellent volumetric capacitance and an ultra-high power density. The electrochemical performance of MSCs could be correlated with the charge carrier mobility within the differently employed GNRs, as determined by pump-probe terahertz spectroscopy studies.

3.
Chem Asian J ; 2020 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-32955160

RESUMO

Chiral graphene nanoribbons represent an important class of graphene nanomaterials with varying combinations of armchair and zigzag edges conferring them unique structure-dependent electronic properties. Here, we describe the on-surface synthesis of an unprecedented cove-edge chiral GNR with a benzo-fused backbone on a Au(111) surface using 2,6-dibromo-1,5-diphenylnaphthalene as precursor. The initial precursor self-assembly and the formation of the chiral GNRs upon annealing are revealed, along with a relatively small electronic bandgap of approximately 1.6 eV, by scanning tunnelling microscopy and spectroscopy.

4.
Artigo em Inglês | MEDLINE | ID: mdl-32945038

RESUMO

Graphene nanoribbons (GNRs) are quasi-1D graphene strips, which have attracted attention as a novel class of semiconducting materials for various applications in electronics and optoelectronics. GNRs exhibit unique electronic and optical properties, which sensitively depend on their chemical structures, especially the width and edge configuration. Therefore, precision synthesis of GNRs with chemically defined structures is crucial for their fundamental studies as well as device applications. In contrast to top-down methods, bottom-up chemical synthesis using tailor-made molecular precursors can achieve atomically precise GNRs. Here, the synthesis of GNRs on metal surfaces under ultrahigh vacuum (UHV) and chemical vapor deposition (CVD) conditions is the main focus, and the recent progress in the field is summarized. The UHV method leads to successful unambiguous visualization of atomically precise structures of various GNRs with different edge configurations. The CVD protocol, in contrast, achieves simpler and industry-viable fabrication of GNRs, allowing for the scale up and efficient integration of the as-grown GNRs into devices. The recent updates in device studies are also addressed using GNRs synthesized by both the UHV method and CVD, mainly for transistor applications. Furthermore, views on the next steps and challenges in the field of on-surface synthesized GNRs are provided.

5.
Nanoscale ; 12(38): 19681-19688, 2020 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-32996531

RESUMO

Bottom-up approaches exploiting on-surface synthesis reactions allow atomic-scale precision in the fabrication of graphene nanoribbons (GNRs); this is essential for their technological applications since their unique electronic and optical properties are largely controlled by the specific edge structure. By means of a combined experimental-theoretical investigation of some prototype GNRs, we show here that high-resolution electron energy-loss spectroscopy (HREELS) can be successfully employed to fingerprint the details of the GNR edge structure. In particular, we demonstrate how the features of HREEL vibrational spectra - mainly dictated by edge CH out-of-plane modes - are unambiguously related to the GNR edge structure. Moreover, we single out those modes which are localized at the GNR termini and show how their relative intensity can be related to the average GNR length.

6.
Nat Commun ; 11(1): 3826, 2020 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-32737306

RESUMO

Silicon is a promising anode material for lithium-ion and post lithium-ion batteries but suffers from a large volume change upon lithiation and delithiation. The resulting instabilities of bulk and interfacial structures severely hamper performance and obstruct practical use. Stability improvements have been achieved, although at the expense of rate capability. Herein, a protocol is developed which we describe as two-dimensional covalent encapsulation. Two-dimensional, covalently bound silicon-carbon hybrids serve as proof-of-concept of a new material design. Their high reversibility, capacity and rate capability furnish a remarkable level of integrated performances when referred to weight, volume and area. Different from existing strategies, the two-dimensional covalent binding creates a robust and efficient contact between the silicon and electrically conductive media, enabling stable and fast electron, as well as ion, transport from and to silicon. As evidenced by interfacial morphology and chemical composition, this design profoundly changes the interface between silicon and the electrolyte, securing the as-created contact to persist upon cycling. Combined with a simple, facile and scalable manufacturing process, this study opens a new avenue to stabilize silicon without sacrificing other device parameters. The results hold great promise for both further rational improvement and mass production of advanced energy storage materials.

7.
J Am Chem Soc ; 2020 Aug 24.
Artigo em Inglês | MEDLINE | ID: mdl-32809808

RESUMO

Negatively curved nanographene (NG) 4, having two heptagons and a [5]helicene, was unexpectedly obtained by aryl rearrangement and stepwise cyclodehydrogenations. X-ray crystallography confirmed the saddle-shaped structures of intermediate 3 and NG 4. The favorability of rearrangement over helicene formation following radical cation or arenium cation mechanisms is supported by theoretical calculations. NG 4 demonstrates a reversible mechanochromic color change and solid-state emission, presumably benefiting from its loose crystal packing. After resolution by chiral high-performance liquid chromatography, the circular dichroism spectra of enantiomers 4-(P) and 4-(M) were measured and showed moderate Cotton effects at 350 nm (|Δε| = 148 M-1 cm-1).

8.
Nat Commun ; 11(1): 3976, 2020 08 07.
Artigo em Inglês | MEDLINE | ID: mdl-32769970

RESUMO

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.

9.
Chemistry ; 2020 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-32786130

RESUMO

The synthesis of unsubstituted oligo- para -phenylenes ( OPP ) exceeding para -hexaphenylene - in the literature often referred to as p -sexiphenyl - has long remained elusive due to their insolubility. We report the first preparation of unsubstituted para -nonaphenylenes ( 9PP s) by extending our precursor route to poly- para -phenylenes ( PPP ) to a discrete oligomer. Two geometric isomers of methoxylated syn - and anti -cyclohexadienylenes were synthesized, from which 9PP was obtained via thermal aromatization in thin films. 9PP was characterized via optical and infrared spectroscopy as well as atomic force microscopy and compared to polymeric analogues. Due to the lack of substitution, para -nonaphenylene, irrespective of the precursor isomer employed, displays pronounced aggregation in the solid state. Intermolecular electronic coupling leads to formation of H-type aggregates, red-shifting emission of the films to greenish. 9PP allows to study the structure-property relationship of para -phenylene oligomers and polymers, especially since the optical properties of PPP depend on the molecular shape of the precursor. [1-3] .

10.
Nano Lett ; 2020 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-32787158

RESUMO

Exact positioning of sublattice imbalanced nanostructures in graphene nanomaterials offers a route to control interactions between induced local magnetic moments and to obtain graphene nanomaterials with magnetically nontrivial ground states. Here, we show that such sublattice imbalanced nanostructures can be incorporated along a large band gap armchair graphene nanoribbon on the basis of asymmetric zigzag edge extensions, achieved by incorporating specifically designed precursor monomers. Scanning tunneling spectroscopy of an isolated and electronically decoupled zigzag edge extension reveals Hubbard-split states in accordance with theoretical predictions. Mean-field Hubbard-based modeling of pairs of such zigzag edge extensions reveals ferromagnetic, antiferromagnetic, or quenching of the magnetic interactions depending on the relative alignment of the asymmetric edge extensions. Moreover, a ferromagnetic spin chain is demonstrated for a periodic pattern of zigzag edge extensions along the nanoribbon axis. This work opens a route toward the fabrication of graphene nanoribbon-based spin chains with complex magnetic ground states.

11.
Chemistry ; 2020 Jun 17.
Artigo em Inglês | MEDLINE | ID: mdl-32741022

RESUMO

Chrysene and its bisbenzannulated homologue, naphtho[2,3-c]tetraphene, were synthesized through a PtCl2 -catalyzed cyclization of alkynes, which also furnished corresponding biaryls subsequent to a Glaser coupling reaction of the starting alkynes. The optoelectronic properties of 5,5'-bichrysenyl and 6,6'-binaphtho[2,3-c]tetraphene were compared to their chrysene-based "monomers". Oxidative cyclodehydrogenations of bichrysenyl and its higher homologue towards large nanographenes were also investigated.

12.
J Am Chem Soc ; 142(30): 12916-12920, 2020 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-32668154

RESUMO

The hydrogenation of hexaphenylbenzene was studied, affording novel partially hydrogenated hexacyclohexylbenzene (HCB) as well as fully hydrogenated 1,2,3,4,5,6-hexacyclohexylcyclohexane (HCC) as an unprecedented "oligocyclohexyl" molecule. The reaction process was analyzed by mass spectrometry with atmospheric pressure chemical ionization and high-performance liquid chromatography. From a crude product mixture, two different crystals with flake- and block-shapes could be grown and analyzed by X-ray crystallography, revealing their structures as HCB and HCC. While a geared arrangement of cyclohexyl substitutes was found in HCB, two isomeric structures were identified in HCC crystal with chair and twist-boat conformations of the central cyclohexane.

13.
J Am Chem Soc ; 142(30): 12925-12929, 2020 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-32662993

RESUMO

Fully conjugated ladder polymers (CLP) possess unique optical and electronic properties and are considered promising materials for applications in (opto)electronic devices. Poly(indenoindene) is a CLP consisting of an alternating array of five- and six-membered rings, which has remained elusive so far. Here, we report an on-surface synthesis of oligo(indenoindene) on Au(111). Its structure and a low electronic band gap have been elucidated by low-temperature scanning tunneling microscopy and spectroscopy and noncontact atomic force microscopy, complemented by density functional theory calculations. Achieving defect-free segments of oligo(indenoindene) offers exclusive insight into this CLP and provides the basis to further synthetic approaches.

14.
Chem Commun (Camb) ; 56(61): 8663-8666, 2020 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-32608398

RESUMO

Amphiphilic polyphenylene dendrimers (PPDs) with distinct lipophilic and positively or negatively charged surface groups were adsorbed onto liposomes and their impact on protein adsorption in blood plasma was studied. The PPD corona reduced binding of specific opsonins and increased the adsorption of proteins controlling cellular uptake based on their surface patches.

15.
Artigo em Inglês | MEDLINE | ID: mdl-32492236

RESUMO

Chemical reduction of a benzo-fused double [7]helicene (1) with two alkali metals, K and Rb, provided access to three different reduced states of 1. The doubly-reduced helicene 12- has been characterized by single-crystal X-ray diffraction as a solvent-separated ion triplet with two potassium counterions. The triply- and tetra-reduced helicenes, 13- and 14- , have been crystallized together in an equimolar ratio and both form the contact-ion complexes with two Rb+ ions each, leaving three remaining Rb+ ions wrapped by crown ether and THF molecules. As structural consequence of the stepwise reduction of 1, the central axis of helicene becomes more compressed upon electron addition (1.42 Šin 14- vs. 2.09 Šin 1). This is accompanied by an extra core twist, as the peripheral dihedral angle increases from 16.5° in 1 to 20.7° in 14- . Theoretical calculations provided the pattern of negative charge build-up and distribution over the contorted helicene framework upon each electron addition, and the results are consistent with the X-ray crystallographic and NMR spectroscopic data.

16.
J Am Chem Soc ; 142(28): 12046-12050, 2020 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-32589416

RESUMO

Coronoids, polycyclic aromatic hydrocarbons with geometrically defined cavities, are promising model structures of porous graphene. Here, we report the on-surface synthesis of C168 and C140 coronoids, referred to as [6]- and [5]coronoid, respectively, using 5,9-dibromo-14-phenylbenzo[m]tetraphene as the precursor. These coronoids entail large cavities (>1 nm) with inner zigzag edges, distinct from their outer armchair edges. While [6]coronoid is planar, [5]coronoid is not. Low-temperature scanning tunneling microscopy/spectroscopy and noncontact atomic force microscopy unveil structural and electronic properties in accordance with those obtained from density functional theory calculations. Detailed analysis of ring current effects identifies the rings with the highest aromaticity of these coronoids, whose pattern matches their Clar structure. The pores of the obtained coronoids offer intriguing possibilities of further functionalization toward advanced host-guest applications.

17.
Angew Chem Int Ed Engl ; 59(33): 14014-14018, 2020 Aug 10.
Artigo em Inglês | MEDLINE | ID: mdl-32363672

RESUMO

Photodynamic therapy (PDT) exhibits great potential for cancer therapy, but still suffers from nonspecific photosensitivity and poor penetration of photosensitizer. Herein, a smart perylene monoimide-based nanocluster capable of enzyme-triggered disassembly is reported as an activatable and deeply penetrable photosensitizer. A novel carboxylesterase (CE)-responsive tetrachloroperylene monoimide (P1) was synthesized and assembled with folate-decorated albumins into a nanocluster (FHP) with a diameter of circa 100 nm. Once P1 is hydrolyzed by the tumor-specific CE, FHP disassembles into ultrasmall nanoparticles (ca. 10 nm), facilitating the deep tumor penetration of FHP. Furthermore, such enzyme-triggered disassembly of FHP leads to enhanced fluorescence intensity (ca. 8-fold) and elevated singlet oxygen generation ability (ca. 4-fold), enabling in situ near-infrared fluorescence imaging and promoted PDT. FHP permits remarkable tumor inhibition in vivo with minimal side effects through imaging-guided, activatable, and deep PDT. This work confirms that this cascaded multifunctional control through enzyme-triggered molecular disassembly is an effective strategy for precise cancer theranostics.

18.
J Am Chem Soc ; 142(23): 10291-10296, 2020 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-32428409

RESUMO

Multiple fused pentagon-heptagon pairs are frequently found as defects at the grain boundaries of the hexagonal graphene lattice and are suggested to have a fundamental influence on graphene-related materials. However, the construction of sp2-carbon skeletons with multiple regularly fused pentagon-heptagon pairs is challenging. In this work, we found that the pentagon-heptagon skeleton of azulene was rearranged during the thermal reaction of an azulene-incorporated organometallic polymer on Au(111). The resulting sp2-carbon frameworks were characterized by high-resolution scanning probe microscopy techniques and feature novel polycyclic architectures composed of multiple regularly fused pentagon-heptagon pairs. Moreover, the calculated analysis of its aromaticity revealed a peculiar polar electronic structure.

19.
Adv Mater ; : e2001268, 2020 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-32378243

RESUMO

Van der Waals heterostructures (VDWHs), obtained via the controlled assembly of 2D atomically thin crystals, exhibit unique physicochemical properties, rendering them prototypical building blocks to explore new physics and for applications in optoelectronics. As the emerging alternatives to graphene, monolayer transition metal dichalcogenides and bottom-up synthesized graphene nanoribbons (GNRs) are promising candidates for overcoming the shortcomings of graphene, such as the absence of a bandgap in its electronic structure, which is essential in optoelectronics. Herein, VDWHs comprising GNRs onto monolayer MoS2 are fabricated. Field-effect transistors (FETs) based on such VDWHs show an efficient suppression of the persistent photoconductivity typical of MoS2 , resulting from the interfacial charge transfer process. The MoS2 -GNR FETs exhibit drastically reduced hysteresis and more stable behavior in the transfer characteristics, which is a prerequisite for the further photomodulation of charge transport behavior within the MoS2 -GNR VDWHs. The physisorption of photochromic molecules onto the MoS2 -GNR VDWHs enables reversible light-driven control over charge transport. In particular, the drain current of the MoS2 -GNR FET can be photomodulated by 52%, without displaying significant fatigue over at least 10 cycles. Moreover, four distinguishable output current levels can be achieved, demonstrating the great potential of MoS2 -GNR VDWHs for multilevel memory devices.

20.
Artigo em Inglês | MEDLINE | ID: mdl-32350979

RESUMO

Cumulene compounds are notoriously difficult to prepare and study because their reactivity increases dramatically with the increasing number of consecutive double bonds. In this respect, the emerging field of on-surface synthesis provides exceptional opportunities because it relies on reactions on clean metal substrates under well-controlled ultrahigh-vacuum conditions. Here we report the on-surface synthesis of a polymer linked by cumulene-like bonds on a Au(111) surface via sequential thermally activated dehalogenative C-C coupling of a tribenzoazulene precursor equipped with two dibromomethylene groups. The structure and electronic properties of the resulting polymer with cumulene-like pentagon-pentagon and heptagon-heptagon connections have been investigated by means of scanning probe microscopy and spectroscopy methods and X-ray photoelectron spectroscopy, complemented by density functional theory calculations. Our results provide perspectives for the on-surface synthesis of cumulene-containing compounds, as well as protocols relevant to the stepwise fabrication of carbon-carbon bonds on surfaces.

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