Spin-ordered electronic states in hydrogen-terminated zigzag nanographene give rise to magnetic quantum phenomena 1,2 that have sparked renewed interest in carbon-based spintronics 3,4 . Zigzag graphene nanoribbons (ZGNRs)quasi one-dimensional semiconducting strips of graphene featuring two parallel zigzag edges along the main axis of the ribbonare predicted to host intrinsic electronic edge states that are ferromagnetically ordered along the edges of the ribbon and antiferromagnetically coupled across its width 1,2,5 . Despite recent advances in the bottom-up synthesis of atomically-precise ZGNRs, their unique electronic structure has thus far been obscured from direct observations by the innate chemical reactivity of spin-ordered edge states [6][7][8][9][10][11] . Here we present a general technique for passivating the chemically highly reactive spin-polarized edge states by introducing a superlattice of substitutional nitrogen-dopants along the edges of a ZGNR. First-principles GW calculations and scanning tunneling spectroscopy reveal a giant spin splitting of the low-lying nitrogen lone-pair flat bands by a large exchange field (~850 Tesla) induced by the spin-polarized ferromagnetically ordered edges of ZGNRs. Our findings directly corroborate the nature of the predicted emergent magnetic order in ZGNRs and provide a robust platform for their exploration and functional integration into nanoscale sensing and logic devices [11][12][13][14][15][16][17] .Graphene nanostructures terminated by zigzag edges host spin-ordered electronic states that give rise to quantum magnetism 1,2 . These intrinsic magnetic edge states emerge from the zigzag edge structure of graphene itself, and create opportunities for the exploration of carbon-based spintronics and qubits [18][19][20] , paving the way for the realization of high-speed, low-power operation spin-logic devices for data storage and information processing [21][22][23][24] . The edge states of zigzag graphene nanoribbons (ZGNRs) have been predicted to exhibit a parallel (ferromagnetic) alignment of spins on either edge of the ribbon while the spins on opposing edges are antiferromagnetically coupled (antiparallel alignment) 1,2 . This unusual electronic structure can give rise to field-or strain-driven half-metallicity in ZGNRs 2,25 . A strong hybridization of the electronic states of ZGNRs with those of the underlying support, along with the susceptibility of zigzag edges to undergo passivation through atom-abstraction or radical-recombination reactions represents a veritable challenge to their exploration.

The mechanical stresses that materials experience during use can lead to aging and failure. Recent developments in covalent mechanochemistry have provided a mechanism by which those stresses can be channeled into constructive, rather than destructive, responses, including strengthening in materials. Here, the synthesis and mechanical response of a polymer containing multiple benzocyclobutene (BCB) mechanophores along its backbone are reported. When solutions of the BCB polymer were exposed to the normally destructive elongational flow forces generated by pulsed ultrasonication, the number of intermolecular bond-forming reactions was greater than the number of bondbreaking reactions, leading to a net increase in polymer molecular weight. The molecular weight increase could be turned into gelation by introducing a bismaleimide cross-linker that reacts with the ortho-quinodimethide intermediate generated by mechanically assisted ring opening of the BCB mechanophores and using polymer concentrations in excess of the critical overlap concentration. Unlike a previous mechanically induced gelation of a mechanophore-based polymer, the BCB cross-linking requires no ionic components and represents an attractive, second platform for stress-strengthening materials.T he inevitable stress that almost all materials experience during use leads in many cases to bond breakage, materials aging, and failure, as is reflected in both polymer solutions 1 and solid state polymers. 2 To solve this problem, biological materials have evolved to have the ability to remodel and become stronger in response to otherwise destructive forces. 3,4 This form of mechanical adaptation has provided significant inspiration to current synthetic polymer chemistry efforts. Our group has recently demonstrated that the activation of multiple gem-dibromocyclopropane (gDBC) mechanophores 5 embedded along a polybutadiene backbone turns otherwise destructive chemical responses into constructive responses. 6 When the polymer was exposed to large forces, through either pulsed ultrasonication of polymer solutions or the extrusion of bulk materials, the gDBCs undergo electrocyclic ring-opening reactions to form 2,3-dibromoalkenes that react intermolecularly with carboxylate nucleophiles. The number of intermolecular bond-forming reactions exceeds the number of bond-breaking reactions and leads to a cross-linked polymer network. 6 While the gDBC system represents an important first example of mechanophore-based self-strengthening, the ultimate utility of the approach will depend on the ability to create mechanophore-based systems that match the demands of a particular application. To that end, we sought to develop multi-mechanophore polymers that might overcome the relatively low reactivity of the 2,3-dibromoalkene, 6 the irreversibility of gDBC ring opening in the absence of crosslinking, and the presence of ionic reactants.Because of the substantial recent activity in the realm of covalent polymer mechanochemistry, 7−9 and especially the exploration of mechanophor...

The majority of Sn-mediated cyclizations are reductive and, thus, cannot give a fully conjugated product. This is a limitation in the application of Sn-mediated radical cascades for the preparation of fully conjugated molecules. In this work, we report an oxidatively terminated Bu3Sn-mediated cyclization of an alkyne where AIBN, the commonly used initiator, takes on a new function as an oxidative agent. Sn-mediated radical transformation of biphenyl aryl acetylenes into functionalized phenanthrenyl stannanes can be initiated via two potentially equilibrating vinyl radicals, one of which can be trapped by the fast 6-endoclosure at the biphenyl moiety in good to excellent yields. The efficient preparation of Sn-substituted phenanthrenes opens access to convenient building blocks for the construction of larger polyaromatics.

Atomically precise bottom-up synthesized graphene nanoribbons (GNRs) are promising candidates for next-generation electronic materials. The incorporation of these highly tunable semiconductors into complex device architectures requires the development of synthetic tools that provide control over the absolute length, the sequence, and the end-groups of GNRs. Here, we report the living chaingrowth synthesis of chevron-type GNRs (cGNRs) templated by a poly-(arylene ethynylene) precursor prepared through ring-opening alkyne metathesis polymerization (ROAMP). The strained triple bonds of a macrocyclic monomer serve both as the site of polymerization and the reaction center for an annulation reaction that laterally extends the conjugated backbone to give cGNRs with predetermined lengths and endgroups. The structural control provided by a living polymer-templated synthesis of GNRs paves the way for their future integration into hierarchical assemblies, sequence-defined heterojunctions, and well-defined single-GNR transistors via block copolymer templates.

The scope of graphene nanoribbon (GNR) structures accessible through bottom-up approaches is defined by the intrinsic limitations of either all-on-surface or all-solution-based synthesis. Here, we report a hybrid bottom-up synthesis of GNRs based on a Matrix-Assisted Direct (MAD) transfer technique that successfully leverages technical advantages inherent to both solution-based and on-surface synthesis while sidestepping their drawbacks. Critical structural parameters tightly controlled in solution-based polymerization reactions can seamlessly be translated into the structure of the corresponding GNRs. The transformative potential of the synergetic bottom-up approaches facilitated by the MAD transfer techniques is highlighted by the synthesis of chevron-type GNRs (cGNRs) featuring narrow length distributions and a nitrogen core-doped armchair GNR (N 4 -7-ANGR) that remains inaccessible using either a solution-based or an on-surface bottom-up approach alone.