On surface π-electron systems: New class of Molecule
Paul Yen1*, Wun-Chang Pan1, Yong-He Pang1, Yu-Lun Hung1, Jean Nelson1, Cheng Ping Shiu1, Hideki Okamoto2, Germar Hoffmann1
1Physics, NTHU, Hsinchu, Taiwan
2Chemistry, Okayama University, Japan
* Presenter:Paul Yen, email:lifesky330@hotmail.com
The technology to down-scale microchip devices such as traditional semiconductor is approaching its limits and the precise design at the atomic scale challenging. Meanwhile, an alternative, bottom-up approach is developing in fundamental research between Chemistry and Physics. Extending π-electron systems[1] through organic synthesis provides a potential platform for atomically defined systems as relevant for organic electronics. Current goal is to deepen our understanding of structure-related physical properties for the realization of efficient devices [2] and proceed in the development of new coupling reactions.
The class of Phenacene is established as a suitable compound for organic field effect transistors. Here, we study 2nd generation, substituted Phenacenes with functionalized groups specifically alkyl- and various Br- substituted Phenacanes, and their precursors, ethylene bridged Naphthalenes, as prepared on Au(111) and Ag(111). In STM, the formation of molecular networks and in STS, the dependence of the electronic structure with substituents are addressed. Thermally treated, Br-substituted Phenacenes show covalent coupling – known as on-surface-synthesis – with characteristic variations depending on the site of the Br-substituents.
Our obtained findings in STM, STS and coupling reactions experiments for different Phenacenes will be compared and discussed in terms of suitability for future progress. Thereby, a new covalent coupling routine based on methyl-Br is identified and latest results presented.

[1] Jie Su et al. Atomically precise bottom-up synthesis of π-extended [5]triangulene. Science Advances 2019;5
[2] Okamoto, H., Hamao, S., Eguchi, R. et al. Synthesis of the extended phenacene molecules, [10]phenacene and [11]phenacene, and their performance in a field-effect transistor. Sci Rep 9, 4009 (2019)

Keywords: STM, STS, Molecule, Au(111)