A team of international scientists led by of Francesca Moresco (Center for Advancing Electronics Dresden – cfaed at TU Dresden) and Diego Peña Gil (Center for Research in Biological Chemistry and Molecular Materials – CiQUS at University of Santiago de Compostela) has achieved a breakthrough in the field of π-electron structures research. For the first time, they synthesised a chain of twelve benzene rings, called dodecacene, which is the longest acene ever obtained to date. This was made possible by using on-surface synthesis and observed by scanning tunneling microscopy. The investigation of the properties of higher acenes also revealed an unexpected increase in the energy gap of dodecacene. The scientists have now published their results in the journal "ACS Nano".

An international team of researchers from TU Dresden, University of Santiago de Compostela, and CEMES-CNRS Institute in Toulouse has succeeded in synthesising a chain of twelve benzene rings, the so-called dodecane by on-surface deoxygenation of a stable precursor molecule. Using scanning tunnelling microscopy and spectroscopy, the researchers also examined the electronic properties of dodecacenes. Surprisingly, their experiments showed that the energy gap remains constant for decacenes and undecacenes, but increases again for dodecacene. This phenomenon is particularly interesting for future research in molecular electronics and spintronics. The results of the research efforts have now been published in the journal "ACS Nano".

What are acenes and why are higher acenes so relevant but complicated?

Acenes are organic compounds, more precisely polycyclic aromatic hydrocarbons consisting of a varying number of linear fused benzene rings. The acene series represents a model system to investigate the intriguing electronic properties of extended π-electron structures in the one-dimensional limit, which are important for applications in electronics and spintronics and for the fundamental understanding of electronic transport.

Especially higher acene series are currently of great interest in research because of their special electronic properties. Recent research efforts suggest a higher radical character as well as the stabilisation of the optical excitation energy for an increasing number of secured benzene rings, which is very attractive for nanoelectronic devices. However, they are difficult to synthesise, because they are chemically very reactive, therefore unstable, and not soluble.

Project and research group

The research was conducted within the framework of the “Planar atomic and molecular scale devices project” (PAMS) EU project. After several years of work with the aim of investigating higher acene series, this has now been completed. The cfaed scientists Frank Eisenhut (former PhD student), Tim Kühne (PhD student) and Francesca Moresco (group leader of the Single Molecule Machines Group at cfaed) were part of this research team. TU Dresden’s Gianaurelio Cuniberti from the Institute for Materials Science has also contributed to the project.
 

Paper:
"Dodecacene Generated on Surface: Reopening of the Energy Gap", pub. in ACS Nano, vol. 14, no. 1, pp. 1011-1017, 2020.
DOI: https://pubs.acs.org/doi/10.1021/acsnano.9b08456
Authors: Frank Eisenhut, Tim Kühne, Fátima García, Saleta Fernández, Enrique Guitián, Dolores Pérez, Georges Trinquier, Gianaurelio Cuniberti, Christian Joachim, Diego Peña, Francesca Moresco

Image:
Download under https://bit.ly/2Ssy4aq
Image caption: STM image and schematic representation of dodecacene overlap in this figure. Twelve bright lobes, representing the 12 benzene rings, are well distinguishable.

Links:

• Single Molecule Machines Group, cfaed, TU Dresden (Dr. Francesca Moresco): https://cfaed.tu-dresden.de/francesca-moresco-group/home
• DCMS, TU Dresden (Prof. Gianaurelio Cuniberti): https://dcms.tu-dresden.de/de/
• Center for Research in Biological Chemistry and Molecular Materials (CiQUS, Diego Peña Gil): https://www.usc.es/ciqus/en/groups/commo
• PAMS project: http://pams-project.eu/

Media inquiries:
Dr. Francesca Moresco, cfaed, Research Group Leader Single Molecule Machines
Phone: +49 351 463-43968
Email: francesca.moresco @ tu-dresden.de

Matthias Hahndorf, cfaed, science communications
Phone: +49 351 - 463 42847
Email: matthias.hahndorf @ tu-dresden.de