Design, synthesis, study and applications of distorted nanographenes

Project Information

NANOGRAPHOUT

Grant agreement ID: 677023

DOI

10.3030/677023

Project closed

EC signature date 18 December 2015

Start date 1 April 2016

End date 30 September 2022

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 492 675,00

EU contribution

€ 1 492 675,00

Coordinated by

UNIVERSIDAD DE GRANADA
Spain

Periodic Reporting for period 4 - NANOGRAPHOUT (Design, synthesis, study and applications of distorted nanographenes)

Reporting period: 2020-10-01 to 2022-09-30

Summary of the context and overall objectives of the project

Graphene is considered as a new starting point for new technologies applicable in different fields. It exhibits unique properties: it is the thinnest and strongest compound known and the lightest material. It is extremely flexible, impermeable to molecules, extremely electrical and thermal conductive and a transparent conductor. Graphene is constituted by a single layer of carbon atoms arranged in a flat hexagonal lattice. However, for many potential applications, such as sensors, energy storage or catalysis, this perfect hexagonal structure is chemically little active and actually it is the presence of intrinsic irregularities what leads to better properties. Understanding the influence of structural imperfections can pave the way for designing defective graphene for particular applications. Among the different production methods of graphene, direct chemical synthesis it is the choice to create small graphene structures with well-defined geometries. Using this approach, we aim to prepare distorted nanographenes containing seven- and higher membered rings into an otherwise planar hexagonal lattice as a new tool for the preparation of innovative materials for organic electronics. These defects induce a curvature in the planar sheet, distorting the structure out of the plane. In particular medium-size rings such as heptagons and octagons induce a saddle-shape curvature in the carbon network. NANOGRAPHOUT focuses on providing a general synthetic method for the construction of a variety of distorted nanographenes with good control on size, shape and the edges of the final compounds as well as number and position of non-hexagonal rings. Combination of defects in also contemplating, as the simultaneously introduction of heptagonal carbocycles with helical moieties. By evaluating the morphology, optical and electronic properties and electron transport of synthesized nanographenes, we aim to establish the first comprehensive study clarifying the influence of defects on the properties of nanographenes. Adding chiroptical response to the semiconductor properties of nanographenes will provide the new devices the added value of their potential application in photonics.

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

We have established a versatila bottom-up approach to prepare functionalized saddle-shaped nanographenes (NGs) incorporating heptagonal carbocycles in the hexagonal network. We also succeeded in the preparation of highly distorted octagon- and unique nonagon containing NGs causing deep distortions in the hexagonal network.
This methodology has proved to be very efficient and been exploited for the preparation of a completely new family of NGs, namely saddle-helix hybrid compounds, leading to the first NG described as chiral emitter. Remarkably, unprecedented combination of optical properties in graphene-related materials have been presented: upconversion based on two-photon absorption (TPA-UC) together with circularly polarized luminescence (CPL). We have demonstrated the effect of the saddle geometry on the TPA response enhancement in nanographenes. This fact could be extended to GQDs and might be one of the cause of their high TPA levels.
We have presented the first fully π-extended [7]helicene, namely, a fully helical ribbon. Fine structural tuning can modulate the optical response, leading to the first superhelicene that exhibits near-infrared NIR-CPL emission both in solution and thin-film.
We have studied the supramolecular chemistry of saddle-shaped NG where low self-association constants are observed and C70 is one of the best guests. In this sense, the incorporation of saddle-NGs into a flexible macrocycle allows their assembly with fullerenes, with selectivity for C70 vs C60. Furthermore the supramolecular assembly of saddle NGs with Ru complexes leads to stabilized Ru-nanoparticles acting as efficient aromatic hydrogenation catalyst.
The incorporation of heptagonal carbocycles as end-groups with [3]cumulene as spacers results in the aggregation-induced emission of [3]cumulenes and their incorporation as end-groups in typical diradical PAHs allows the establishment of a clear correlation between electronic and molecular structures. The first examples of organic radicals as CPL emitters in solution have been reported, including a new derivative acting as magnetic CPL emitter with a high racemization barrier.
The influence of the presence of defects on the electron transport through PAHs has also been studied in particular cases leading to interesting conclusions: i) BN-doping does not affect the electron transport through acene-like derivatives while stabilizing highly reactive all-carbon analogues; ii) N-doping of conjugated OPEs leads to the generation of additional conduction pathways in a single molecule.
We have also focused on the on-surface synthesis (OSS) of distorted graphene nanostructures as a way to modulate the optoelectronic/magnetic properties of the final assemblies. In this sense, heptagonal rings as tropone moieties are thermally transformed into hexagonal or pentagonal rings.

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)

As a general conclusion, we can say that our methodology can be exploited for the preparation and extension of highly distorted nanographenes,
thus creating a new family of well-defined saddle-helix hybrid PAHs with high solubility and an outstanding combination of optical, chiroptical and electrochemical properties.

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