On-surface synthesis of higher acenes beyond undecacene: Evolution of conductance and electronic states

• Applicant: Dr. Francesca Moresco
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 432345501

Acenes are a class of polycyclic aromatic hydrocarbons with linearly fused benzene rings. They are widely considered as promising materials for organic and molecular electronics. The nature of their electronic structure is presently actively discussed and fundamental questions regarding the electronic configuration of their ground state as a function of the number of rings are not answered yet. The present high interest in acenes is mainly motivated by the expected increasing radical character as well as the reduced optical excitation barrier for an increasing number of rings. The POLYACENES project is established to understand the energy gap development and the radical character of the ground state of higher acenes as a function of the number of linearly fused benzene rings. The goal of the project is to experimentally determine the electronic properties and the conductance of oligoacenes synthetized on surface, studying the evolution of the electronic resonances and the decay of the tunneling current. High-resolution scanning tunneling microscopy (STM) at low temperature is employed to verify the chemical conversion at a single-molecule level.In POLYACENES, we aim to continue the series of acenes synthetized on surface to 12 cene, 14 cene, and longer. Scanning tunneling spectroscopy will give access to the energy position and spatial distribution of the electronic states, determining the evolution of the electronic resonances. To gain further information on the open shell character of the new long acenes, we will combine the study of gap and electronic resonances with lateral manipulation experiments. We will use the obtained long acene molecules for conductance measurements. By pulling one end of the molecule with the apex of the STM, we will record the tunneling current in non-resonant regime studying the evolution of the conductance with the molecular length and the effect of conjugation. Moreover, we will investigate the role of the substrate in the on-surface synthesis of acenes and the effect of decoupling via a passivating H-layer on Si(001).

• DFG Programme: Research Grants
• International Connection: Spain
• Cooperation Partner: Professor Dr. Diego Peña