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December 2017

Real-space visualization of conformation-independent oligothiophene electronic structure

FIG. 2. Model of 8T and 7T molecules from Fig. 1 matched to the Au(111) surface lattice. ((a)-(d)) STM images [set point 100 mV, 5 pA] of sub-areas from Figs. 1(a)-1(c). ((e)-(h)) Models of oligothiophene molecules from (a)-(d) overlaid on the Au(111) lattice. Crystallographic directions are indi- cated. Black dashed circles indicate the van der Waals radii of the hydrogen atoms. Red dashed circles for the highlighted molecules indicate S atoms on or near Au top-sites (as opposed to bridging or hollow sites).

We present scanning tunneling microscopy and spectroscopy (STM/STS) investigations of the electronic structures of di erent alkyl-substituted oligothiophenes on the Au(111) surface. STM imaging showed that on Au(111), oligothiophenes adopted distinct straight and bent conformations. By combining STS maps with STM images, we visualize, in real space, particle-in-a-box-like oligothiophene molecular orbitals. We demonstrate that di erent planar conformers with signi cant geometrical distortions of oligothiophene backbones surprisingly exhibit very similar electronic structures, indicating a low degree of conformation-induced electronic disorder. The agreement of these results with gas-phase density functional theory calculations implies that the oligothiophene interaction with the Au(111) surface is generally insensitive to molecular conformation.

The Journal of Chemical Physics 144, 194703 (2016); doi: 10.1063/1.4949765

Benjamen N. Taber,1 Dmitry A. Kislitsyn,1 Christian F. Gervasi,1 Jon M. Mills,1 Ariel E. Rosenfield,1 Lei Zhang,2 Stefan C. B. Mannsfeld,3 James S. Prell,1 Alejandro L. Briseno,2 and George V. Nazin1

1. Department of Chemistry and Biochemistry, Materials Science Institute, Oregon Center for Optical, Molecular and Quantum Science, University of Oregon, 1253 University of Oregon, Eugene, Oregon 97403, USA

2. Department of Polymer Science and Engineering, Silvio O. Conte National Center for Polymer Research, University of Massachusetts-Amherst, 120 Governors Drive, Amherst, Massachusetts 01003, USA

3. Center for Advancing Electronics Dresden, Dresden University of Technology, 01062 Dresden, Germany

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