Local electronic and chemical structure of oligo-acetylene derivatives formed through radical cyclizations at a surface

A. Riss,1 S. Wickenburg, P. Gorman, L. Z. Tan, H.-Z. Tsai, D. G. de Oteyza, Y.-C. Chen, A. J. Bradley, M. M. Ugeda, G. Etkin, S. G. Louie, F. R. Fischer, M. F. Crommie

Department of Physics, University of California, Berkeley, CA 94720, U. S. A.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, U. S. A.
Department of Chemistry, University of California, Berkeley, CA 94720, U. S. A.
Centro de Física de Materiales CSIC/UPV-EHU-Materials Physics Center, 20018 SanSebastián, Spain
1 Present address: Institut für Angewandte Physik, Technische Universität Wien, 1040 Wien, Austria

Nano Lett. 14 (2014) 2251-2255

Semiconducting pi-conjugated polymers have attracted significant interest for applications in light-emitting diodes, field-effect transistors, photovoltaics, and nonlinear optoelectronic devices. Central to the success of these functional organic materials is the facile tunability of their electrical, optical, and magnetic properties along with easy processability and the outstanding mechanical properties associated with polymeric structures. In this work we characterize the chemical and electronic structure of individual chains of oligo-(E)-1,1'-bi(indenylidene), a polyacetylene derivative that we have obtained through cooperative C1-C5 thermal enediyne cyclizations on Au(111) surfaces followed by a step-growth polymerization of the (E)-1,1'-bi(indenylidene) diradical intermediates. We have determined the combined structural and electronic properties of this class of oligomers by characterizing the atomically precise chemical structure of individual monomer building blocks and oligomer chains (via noncontact atomic force microscopy (nc-AFM)), as well as by imaging their localized and extended molecular orbitals (via scanning tunneling microscopy and spectroscopy (STM/STS)). Our combined structural and electronic measurements reveal that the energy associated with extended pi-conjugated states in these oligomers is significantly lower than the energy of the corresponding localized monomer orbitals, consistent with theoretical predictions.

Corresponding authors: Felix R. Fischer and Michael F. Crommie.

Experimental data from this work were used for the cover page of this issue of Nano Letters. This work was also chosen as Result of the Month by Omicron Nanotechnology.

You can download a PDF file of this open-access article from Nano Letters or from the IAP/TU Wien web server.