Freie Universität Berlin, Fachbereich Physik, Berlin, Germany.
J Phys Condens Matter. 2012 Sep 5;24(35):354003. doi: 10.1088/0953-8984/24/35/354003. Epub 2012 Aug 16.
Electronic doping is a key concept for tuning the properties of organic materials. In bulk structures, the charge transfer between donor and acceptor is mainly given by the respective ionization potential and electron affinity. In contrast, monolayers of charge transfer complexes in contact with a metal are affected by an intriguing interplay of hybridization and screening at the metallic interface, determining the resulting charge state. Using scanning tunneling microscopy and spectroscopy, we characterize the electronic properties of the organic acceptor molecule 11,11,12,12-tetracyanonaptho-2,6-quinodimethane (TNAP) adsorbed on a Au(111) surface. The ordered islands remain in a weakly physisorbed state with no charge transfer interaction with the substrate. When the electron donor tetrathiafulvalene (TTF) is added, ordered arrays of alternating TNAP and TTF rows are assembled. In these structures, we find the lowest unoccupied molecular orbital (LUMO) of the free TNAP molecule shifted well below the Fermi level of the substrate. The TNAP is thus charged with more than one electron.
电子掺杂是调控有机材料性能的一个关键概念。在体相结构中，给体和受体之间的电荷转移主要由各自的电离势和电子亲合能决定。相比之下，与金属接触的电荷转移复合物单层受到金属界面上杂化和屏蔽的有趣相互作用的影响，决定了最终的电荷状态。我们使用扫描隧道显微镜和光谱学来表征吸附在 Au(111)表面上的有机受体分子 11,11,12,12-四氰基萘醌-2,6-二甲烷（TNAP）的电子性质。有序的岛状结构仍处于弱物理吸附状态，与基底没有电荷转移相互作用。当电子供体四硫富瓦烯（TTF）被添加时，交替排列的 TNAP 和 TTF 行的有序阵列被组装起来。在这些结构中，我们发现自由 TNAP 分子的最低未占据分子轨道（LUMO）明显低于基底的费米能级。因此，TNAP 被充入了一个以上的电子。
