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ERC

SURFINK Report Summary

Project ID: 635919
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - SURFINK (Functional materials from on-surface linkage of molecular precursors)

Reporting period: 2015-09-01 to 2017-02-28

Summary of the context and overall objectives of the project

"The project aims at boosting a newly developing type of chemistry typically termed "on-surface synthesis". It is closely related to heterogeneous catalysis, which addresses the favorable effect of particular supports in reaction processes of industrial or ecologic interest. On-surface synthesis maintains the reaction support of heterogeneous catalysis, normally using atomically well defined surfaces. However, its main goal is complementing conventional organic chemistry by extending its capabilities thanks to the surface confinement of the reactants, since molecules behave and react differently if they float in three-dimensional space (as in the solutions of conventional wet chemistry) or if they are confined to a two dimensional plane. On-surface synthesis can thus be seen as a new methodology or branch within organic chemistry. Apart from the implicit surface support, the rest of the environment can be a solution, controlled atmospheres or vacuum. This project focuses on the latter, providing the cleanest environment for an easier understanding of the reactions, which may in turn facilitate their optimization.
Advancing this new type of chemistry will allow the development of new materials not achievable by conventional means. This may have an important impact in society, given the irrevocable and continuously increasing presence that synthetic materials have gained in our daily lives. In fact, beyond conventional "cheap" plastic use in packaging or as purely structural materials, the variety of their applications is continuously growing, including highly refined functionalities as for example in optoelectronic devices, catalysts, filters or batteries.
Within this project, this new type of chemistry is being brought a step further. The field being still in its infancy, most of the work to date has just demonstrated possible reactions that can be run under these conditions. Going beyond the proof of concept, we are actually using this new type of chemistry to synthesize potentially functional materials like graphene nanoribbons, donor-acceptor frameworks or porous networks. Along the way, we additionally try to develop and improve the still scarcely equipped toolbox of on-surface synthesis by proving new reactions that can be applied, new reaction activation methods that can be used, understanding and optimizing the role of the substrates, trying to use alternative, technologically more attractive substrates, and combinations thereof."

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

"The work performed within this reporting period includes several different aspects.
From an experimental viewpoint, the new laboratory has been set up, including the successful installation of the low temperature scanning probe microscopy system that can be considered the project's "workhorse". In spite of the substantial delivery time of the microscope and the subsequent time required for its careful trimming for satisfactory performance, the project has still progressed continuously making use of the readily available equipment in our home laboratory.
With regard to the particular work packages, the work performed has exceeded the project's outline, summarized as follows:

Package a2.1 Graphene nanoribbons (GNRs): We have tested several precursors for the synthesis of new graphene nanoribbons. Doing so, we have demonstrated for the first time the growth of atomically precise graphene nanoribbons with chiral edge structure on arbitrary metal surfaces. To date, chiral ribbons had been only obtained on Cu(111) surfaces from a precursor designed to render armchair GNRs. In that case, system-specific molecule-substrate interactions cause the molecules to react in an unexpected way that renders chiral GNRs. Inspired in this result, we have designed a precursor that has been proven to render chiral GNRs on Au(111), Ag(111) and Cu(111) alike. Further advantages of this reactant are the low threshold temperature for the activation of the reactions that lead to the GNR formation, as well as their remarkable lengths as compared to other GNRs. The latter makes these nanoribbons particularly interesting for their implementation in devices. These results have been published in ACS Nano 2016, 10, 9000-9008, satisfying deliverable d1. Furthermore, we have characterized their electronic properties on Au(111), which will soon give rise to an additional publication. Using a different precursor, namely dibromoterphenyl, we have also grown poly-paraphenylene wires that we subsequently fused together into atomically precise armchair graphene nanoribbons of different widths depending on the number wires involved. Analysis of the electronic properties as a function of the GNR width has allowed us to understand the energy level alignment of GNR electronic states with respect to model contact materials like gold. A publication on these findings is also in preparation.

Package a2.2 Porous networks: No work was foreseen for this reporting period, and no work has been performed.

Package a2.3 Donor-acceptor networks: We have performed a study on the doping of organic semiconductors with nitrogen heteroatoms. Keeping the same structure of the carbon backbone, we have exchanged an increasing number of carbon atoms by nitrogen. In a subsequent characterization of the electronic properties, we observe how the products of the pristine reactants can be considered p-type semiconductors (donors), while those with increasing N content have lower energy levels as required for n-semiconductors or acceptors. With these results at hand we already have the ingredients to form covalently bonded segments of donor and acceptor semiconducting wires. The results have been published in ACS Nano 2016, 10, 2644-2651, which can be considered the first deliverable of this package, although delivery was planned for the next reporting period (d9 in the description of action or DOA).

Package a2.4.1 New chemical reactions: Performing experiments on enediyne cyclization with new precursors, we have discovered a new reaction involving the ring closure of a diradical benzene unit into a bicyclic olefin whose surface chemistry was hitherto unknown. With respect to the project's final objective of using the new chemistry for the synthesis of functional materials, the reaction does not seem the most convenient, since it quenches two radicals at the intramolecular level and thereby avoids radical step growth polymerization. Nevertheless, it represents interesting new chemistry that advances our understanding of surface-supported chemical reactions. The results have been published in Journal of the American Chemical Society 2016, 138, 10963-10967, satisfying deliverable d13 of the DOA.

Package a2.4.2 Hierarchic self-assembly: No work was foreseen for this reporting period, and no work has been performed.

Package a2.4.3 Reversible reactions: No work was foreseen for this reporting period, and no work has been performed.

Package a2.4.4 Role of the substrate: We have performed our synthesis experiments on a variety of substrates. In doing so, we have succeeded in the alignment of supramolecular structures with surface templates, as for example the chiral GNRs described in package a2.1 and the semiconducting wires described in package a2.3. The latter has readily been published and can be considered as a deliverable of d21 of the DOA, initially planned for the second reporting period. Furthermore, we have preliminary results demonstrating the catalytic role of steps in Au single crystals for Ullmann coupling reactions. These experiments have been performed comparing the reaction on flat Au(111) surfaces and stepped Au(322) surfaces, as well as on curved single crystals with varying step density. The results all hint to an important effect on the reaction and approach the fulfillment of deliverable d20 foreseen for the second reporting period.

Package a2.4.5 Reactions on insulators: Although no work was foreseen for this reporting period, we have successfully demonstrated the occurrence of Ullmann coupling on semiconducting TiO2 surfaces. This is an important step towards the realization of functional materials on top of technologically relevant substrates for electronic applications. The results have been published in Journal of the American Chemical Society 2016, 138, 5685-5692 and readily satisfy deliverable d23, foreseen for a later reporting period."

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

"The project´s progress goes beyond the state of the art along different lines. On the one hand it has achieved the synthesis of new types of graphene nanoribbons (GNRs). GNRs are seen as potentially revolutionary materials for the IT industry, whereby outstanding properties of graphene are combined with a great degree of tunability of their electronic properties. Controlling the exact atomic structure of the ribbons, GNRs can be made semiconducting, metalllic, magnetic, their energy level alignment can be tailored... That is, purely graphene-based integrated circuits are conceivable, whereby one could profit from graphene´s extraordinary properties and of self-assembly productioin methods at the same time. This would revolutionize the conventional IT industry, which would in turn have an important socio-economic impact. Self-assembly may for example allow taking a major step in the miniaturization trend of optoelectronic devices, further made possible by graphene´s reproducible and predictable response to nanoconfinement. However, it all requires the controlled synthesis of GNRs and heterostructures thereof with atomic precision, which is exactly what we are managing in this project.

On the other hand, by gaining a deeper insight into this new type of chemistry performed on surfaces and under vacuum, we set the basis to synthesize new materials not achievable by conventional means. And taking into account the increasing amounts of synthetic materials present in our daily lives, as well as the increasing complexity of their functionalities, this project´s progress brings the potential to boost this "materials revolution", with obvious societal implications like new or optimized functionality of "plastic materials"."
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