Dept. of Physics and Astronomy, University of Nebraska - Lincoln, 855 N 16th Street, Lincoln, NE 68588, USA.
Chem Commun (Camb). 2012 Jul 21;48(57):7143-5. doi: 10.1039/c2cc32462h. Epub 2012 Jun 12.
The permanent dipole of quinonoid zwitterions changes significantly when the molecules adsorb on Ag(111) and Cu(111) surfaces. STM reveals that sub-monolayers of adsorbed molecules can exhibit parallel dipole alignment on Ag(111), in strong contrast with the antiparallel ordering prevailing in the crystalline state and retrieved on Cu(111) surfaces, which minimizes the dipoles electrostatic interaction energy. DFT shows that the rearrangement of electron density upon adsorption is a result of donation from the molecular HOMO to the surface, and back donation to the LUMO with a concomitant charge transfer that effectively reduces the overall charge dipole.
当醌型两性离子分子吸附在 Ag(111) 和 Cu(111) 表面时，其永久偶极矩会发生显著变化。STM 揭示了吸附分子的亚单层在 Ag(111) 上可以表现出平行的偶极定向，与在结晶状态下占主导地位的反平行有序和在 Cu(111)表面上恢复的有序形成鲜明对比，后者最小化了偶极静电相互作用能。DFT 表明，吸附时电子密度的重排是分子 HOMO 向表面的贡献以及与 LUMO 的反向贡献的结果，伴随着有效的电荷转移，从而有效降低了整体电荷偶极矩。
