Seminars Archive

Surface-catalyzed polymer growth in one and two dimensions

Abstract
Conjugated polymers constitute a class of low-dimensional materials of broad scientific interest. While they have been studied and used for several decades, it is only recently that the possibility for surface- controlled polymerization has been investigated. Producing polymers in an ultrahigh vacuum (UHV) environment gives enhanced control of cleanliness and coverage; recent UHV work by other groups has successfully demonstrated surface polymerization using heating as the activation mechanism. However, the use of the surface itself as a catalyst for the surface-confined polymerization reaction has not yet been explored. In the talk I will describe surface confined synthesis of individual conjugated polyphenylene chains by exploiting the classical Ullmann dehalogenation reaction, whereby copper cleaves C- Hal bonds in favour of forming free biradicals and Cu-Hal. The reaction is achieved through deposition and annealing of two isomeric monomers (1,4- and 1,3-diiodobenzene) on the 110 surface of copper, and is subsequently characterized through scanning tunnelling microscopy (STM). We demonstrate that the lines can be grown perfectly straight (for 1,4-diiodobenzene), or with kinks (for 1,3- diiodobenzene) as defined by molecular geometry. As the dehalogenation procedure should work in any geometry, it should be possible to create flat 2D covalently-bonded meshes through choice of a monomer with more than two reactive sites. I will also discuss our recent efforts in growing such structures by use of the monomers 1,3,5- triiodobenzene and tetrathienoanthracene on the 111 facet of copper.