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

并苯是一类具有线性稠合苯环的多环芳烃。它们被广泛认为是有机和分子电子学的有前途的材料。它们的电子结构的性质目前正在积极讨论，关于它们的基态的电子构型作为环数的函数的基本问题还没有得到回答。目前对并苯的高度兴趣主要是由于预期的增加的自由基特性以及减少的光学激发势垒为越来越多的环。POLYACENES项目的建立是为了了解高级并苯基态的能隙发展和自由基特征作为线性稠合苯环数量的函数。该项目的目标是通过实验确定表面合成的低聚并苯的电子性质和电导，研究电子共振的演变和隧穿电流的衰减。高分辨率扫描隧道显微镜（STM）在低温下被用来验证在单分子水平上的化学转化。在POLYACENES中，我们的目标是将表面合成的并苯系列延续到12 cene，14 cene和更长。扫描隧道光谱学将提供电子态的能量位置和空间分布，确定电子共振的演化。为了获得新长并苯的开壳特性的进一步信息，我们将联合收割机的间隙和电子共振的研究与横向操纵实验。我们将使用所获得的长并苯分子进行电导测量。通过用STM的顶点牵拉分子的一端，我们将记录在非共振区的隧穿电流，研究电导随分子长度的演化和共轭效应。此外，我们将研究基板的作用，并苯的表面合成和去耦通过钝化H-层上的Si（001）的效果。

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).