Graphene nanoribbons (GNRs) are excellent candidates for next-generation electronic materials. Unlike GNRs produced by "top-down" methods such as lithographical patterning of graphene and unzipping of carbon nanotubes that cannot reach structural perfection, the fabrication of structurally well-defined GNRs has been achieved by a "bottom-up" organic synthesis via solution-mediated or surface-assisted cyclodehydrogenation. Specifically, non-planar polyphenylene precursors were first "build up" from small molecules, and then "graphitized" and "planarized" to yield GNRs. However, fabrication of processable and longitudinally well-extended GNRs has remained a major challenge. Here we report a "bottom-up" solution synthesis of long (>200 nm), liquid-phase processable GNRs with well-defined structure and a large optical bandgap of 1.88 eV. Scanning probe microscopy demonstrates self-assembled monolayers of GNRs, and non-contact, time-resolved Terahertz conductivity measurements reveal excellent charge-carrier mobility within individual GNRs. Such structurally well-defined GNRs offer great opportunities for fundamental studies into graphene nanostructures, as well as development of GNR-based nanoelectronics.DOI: 10.1038/NCHEM.1819 http://www.nature.com/nchem/journal/v6/n2/abs/nchem.1819.html 2 Graphene nanoribbons (GNRs), defined as nanometre-wide strips of graphene, are attracting increasing attention as highly promising candidates for next generation semiconductor materials 1,2,3,4 . Quantum confinement effects impart GNRs with semiconducting properties, i.e. with a finite bandgap, which critically depends on the ribbon width and its edge structure 1,3 . Fabrication of GNRs has been primarily carried out by "top-down" approaches such as lithographical patterning of graphene 5,6 and unzipping of carbon nanotubes 7,8 , revealing their semiconducting nature and excellent transport properties 1 . However, these methods are generally limited by low yields and lack of structural precision, leading to GNRs with uncontrolled edge structures.In contrast, a "bottom-up" chemical synthetic approach based on solution-mediated 9,10,11,12,13 or surface-assisted 14 cyclodehydrogenation, namely "graphitization" and "planarization", of tailor-made three-dimensional polyphenylene precursors offers an appealing strategy for making structurally well-defined and homogeneous GNRs. The polyphenylene precursors are built up from small molecules, and thus their structures can be tailored within the capabilities of modern synthetic chemistry 15 . However, GNRs (>30 nm) produced by solution-mediated methods have been precluded from unambiguous structural characterization, i.e. microscopic visualization, due to their limited processability 9,12 . On the other hand, GNRs produced by the surface-assisted protocol have been characterized to be atomically precise using scanning tunnelling microscopy (STM) 14 . Nevertheless, this method can only provide a limited amount of GNR material, which is further bound to a metal surface, impeding wide...

Exploiting the properties of two-dimensional crystals requires a mass production method able to produce heterostructures of arbitrary complexity on any substrate. Solution processing of graphene allows simple and low-cost techniques such as inkjet printing to be used for device fabrication. However, the available printable formulations are still far from ideal as they are either based on toxic solvents, have low concentration, or require time-consuming and expensive processing. In addition, none is suitable for thin-film heterostructure fabrication due to the re-mixing of different two-dimensional crystals leading to uncontrolled interfaces and poor device performance. Here, we show a general approach to achieve inkjet-printable, water-based, two-dimensional crystal formulations, which also provide optimal film formation for multi-stack fabrication. We show examples of all-inkjet-printed heterostructures, such as large-area arrays of photosensors on plastic and paper and programmable logic memory devices. Finally, in vitro dose-escalation cytotoxicity assays confirm the biocompatibility of the inks, extending their possible use to biomedical applications.

We first reported that polyvinylpyrrolidone-protected graphene was dispersed well in water and had good electrochemical reduction toward O(2) and H(2)O(2). With glucose oxidase (GOD) as an enzyme model, we constructed a novel polyvinylpyrrolidone-protected graphene/polyethylenimine-functionalized ionic liquid/GOD electrochemical biosensor, which achieved the direct electron transfer of GOD, maintained its bioactivity and showed potential application for the fabrication of novel glucose biosensors with linear glucose response up to 14 mM.