From acenes to nanographenes: generation, structure and electronic properties.

Principal Investigator: Dr hab. Szymon Godlewski
Duration: 2018 - 2023

Rapid development of electronic devices, which we observe in recent years, focuses researcher attention on synthesis of new functional materials. Among them organic semiconductors play a prominent role and the synthesis of new, well-structured molecules is central to development of organic electronics. Acenes, belonging to the arynes family and containing linearly fused benzene rings, are regarded as promising candidates for future applications in photovoltaics, field-effect organic transistors, organic light emitting diodes and other electronic and spintronic devices. These molecules exhibit interesting and intriguing electronic and magnetic properties, which come out with increasing number of annealed rings. In particular it is expected that the already relatively narrow HOMO-LUMO band gap decreases rapidly with increased molecule length. Moreover theoretical analysis indicates that when a dozen rings fuse the ground state is best characterized as open-shell configuration with antiferromagnetic coupling, making the system extremely interesting for quantum analysis. However, the synthesis and analysis of higher acenes is a highly challenging task due to their intrinsic instability and reactivity, which grows with increased length. Up to date a few stabilization strategies have been developed, but it was only recently when the methods based on surface-assisted synthesis allowed for generation and detailed characterization of long parent acenes containing 9 and 10 linearly fused rings. The project will be aimed at synthesis and thorough analysis of structural and electronic properties of higher acenes. Moreover we will synthesize acene-based molecules containing non-hexagonal, 4- and 5-membered rings, which are known to increase the molecule stability, hence enabling preservation of their outstanding electronic properties. Furthermore fine tuning of molecule electronic levels will be achieved based on intentional substitutional doping. In the subsequent step more extended molecular architectures will be constructed directly on a surface based on surface assisted polymerisation of molecular precursors. This will lead to long oligomers with building blocks based on acenes and characterized by a low band gap. Further we will test the possibility of graphene nanoribbons and nanoflakes synthesis based on polymerisation and cyclodehydrogenation of acene-based moieties and finally an attempt to decorate graphene-like nanostructures with non-hexagonal rings periodically embedded will be taken. Noteworthy, we will also work on the synthesis and characterization of molecular nanostructures with exotic electronic properties, including extraordinary intriguing diradical species. All created molecular architectures will be deeply analysed structurally and electronically.