Regulating the complex environment accounting for the stability, selectivity, and activity of catalytic metal nanoparticle interfaces represents a challenge to heterogeneous catalyst design. Here we demonstrate the intrinsic performance enhancement of a composite material composed of gold nanoparticles (AuNPs) embedded in a bottom-up synthesized graphene nanoribbon (GNR) matrix for the electrocatalytic reduction of CO. Electrochemical studies reveal that the structural and electronic properties of the GNR composite matrix increase the AuNP electrochemically active surface area (ECSA), lower the requisite CO reduction overpotential by hundreds of millivolts (catalytic onset > -0.2 V versus reversible hydrogen electrode (RHE)), increase the Faraday efficiency (>90%), markedly improve stability (catalytic performance sustained over >24 h), and increase the total catalytic output (>100-fold improvement over traditional amorphous carbon AuNP supports). The inherent structural and electronic tunability of bottom-up synthesized GNR-AuNP composites affords an unrivaled degree of control over the catalytic environment, providing a means for such profound effects as shifting the rate-determining step in the electrocatalytic reduction of CO to CO, and thereby altering the electrocatalytic mechanism at the nanoparticle surface.
Molybdenum carbyne complexes [RC≡Mo(OC(CH3)(CF3)2)3] featuring a mesityl (R = Mes) or an ethyl (R = Et) substituent initiate the living ring-opening alkyne metathesis polymerization of the strained cyclic alkyne, 5,6,11,12-tetradehydrobenzo[a,e][8]annulene, to yield fully conjugated poly(o-phenylene ethynylene). The difference in the steric demand of the polymer end-group (Mes vs Et) transferred during the initiation step determines the topology of the resulting polymer chain. While [MesC≡Mo(OC(CH3)(CF3)2)3] exclusively yields linear poly(o-phenylene ethynylene), polymerization initiated by [EtC≡Mo(OC(CH3)(CF3)2)3] results in cyclic polymers ranging in size from n = 5 to 20 monomer units. Kinetic studies reveal that the propagating species emerging from [EtC≡Mo(OC(CH3)(CF3)2)3] undergoes a highly selective intramolecular backbiting into the butynyl end-group.
The reticular synthesis of covalent organic frameworks (COFs), extended porous twodimensional (2D) or three-dimensional (3D) networks held together by strong, highly directional chemical bonds, has thus far been restricted to small, shape-persistent, molecular building blocks. Here, we demonstrate the growth of crystalline 2D COFs from a polydisperse macromolecule derived from single-layer graphene, bottom-up synthesized quasi one-dimensional (1D) graphene nanoribbons (GNRs). X-ray scattering and transmission electron microscopy reveal that 2D sheets of GNR-COFs self-assembled at a liquid-liquid interface stack parallel to the layer boundary and exhibit an orthotropic crystal packing. Liquid-phase exfoliation of multilayer GNR-COF crystals gives access to large area (>10 5 nm 2) bilayer and trilayer cGNR-COF films. The functional integration of extended 1D materials into crystalline COFs greatly expands the structural complexity and the scope of mechanical and physical materials properties accessible through a deterministic reticular bottom-up approach.
The design and implementation of carbon-based functional nanoelectronic materials into device architectures relies on the development of synthetic tools capable of providing a precise and reproducible control over the structure of materials at the nanometer scale. Recent advances in the bottom-up synthesis of semiconducting graphene nanoribbons (GNRs), quasi-one dimensional strips of single-layer graphene, have enabled the preparation of carbon-based nanomaterials with exquisite control over the width, [1][2][3][4][5] the crystallographic symmetry (e.g.armchair, [1][2][3][4][5][6][7][8][9][10][11][12][13] zig-zag [14] ), and the edge structure (cove, [15][16] chevron [1,[17][18][19][20] ) both in solution and on metal surfaces. While bottom-up synthesized GNRs have been touted for their intrinsic exotic electronic, [21][22][23][24][25][26][27][28][29][30][31] magnetic, [25,[29][30][31][32] and optical properties, [16,27,28,[33][34] examples for the deterministic assembly of functional bottom-up synthesized GNRs heterostructures have thus far been limited to uncontrolled copolymerization of molecular precursors on metal surfaces [6,13,18,20] or the study of smallmolecule model systems in solution. [35][36][37] We herein report the solution-based bottom-up synthesis and characterization of a GNR heterostructure comprised of two segments of solubilized cove GNRs (cGNRs) linked by a substituted tetraphenylporphyrin core (1, Scheme 1) acting as a highly tunable molecular quantum dot (QD). While our synthetic strategy can be extended to a variety of bifunctional linkers (see Supporting Information), we herein focus on the integration of a disubstituted tetraphenylporphyrin (H2(TPP)) and its metal complexes into a cGNR-H2(TPP)-cGNR heterostructure.Mass spectrometry (MS) and 13 C-NMR spectroscopy of 13 Clabeled poly-phenylene intermediates underscores the exquisite structural control over monomer sequence in the cGNR-H2(TPP)-cGNR heterojunction. Electronic characterization of the resulting metalloporphyrin-cGNR hybrid materials by UV-Vis absorption and fluorescence emission spectroscopy shows strong electronic communication between the porphyrin and cGNR segments. We further demonstrate that reversible binding of primary amine ligands to the axial coordination site of the metalloporphyrin core can serve as a tool to direct the assembly of cGNR-Zn(TPP)-cGNR heterostructures on photolithographically patterned substrates. The deterministic bottom-up synthesis of cGNR-porphyrincGNR heterojunctions is depicted in Scheme 1. 5,15-bis(4-ethynylphenyl)-10,20-diphenylporphyrin (2) serves as the precursor for the porphyrin core in 1. The solubilized cGNR [a]
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