Development of a toolbox of organic synthetic reactions that can be induced on individual molecules by STM

OAK B262 Final Report DOE Grant No.: DE-FG03-01ER15263 ''Development of a toolbox of organic synthetic reactions that can be induced on individual molecules by STM'' Abstract Bommisetty V. Rao, Ki-Young Kwon, Robert Perry, Luke Nysen, Gregory Pavin, Qibin Zhang, Casey Dugger and Ludwig Bartels University of California at Riverside, Pierce Hall, Riverside, CA92521, email: Ludwig.Bartels@ucr.edu The key scientific objective of this project is the development of a set of reliable techniques for the addressal of specific bonds of individual molecules in order to assemble functional molecules on a metal surface at single-atom precision. Success in this direction will open up a conceptually novel route to single molecule chemistry, which can provide its products at any desired surface location without involving any lithographic steps at all. In the course of this project a number of halo-substituted aryls and alkyls where investigated with special concern to two properties: clean deposition of the reactants from the gas phase on metallic surfaces and STM-based addressability of individual substituents of them. In order to prevent contamination of the sample by deposition of solvent residue, a special depositions source was developed that uses a skimmed molecular beam. Exemplary substances studied were 1,3-iodobromobenzene (IBB), 3 bromopropionitrile (BPN) and 4,4'-dibromobiphenyl (DBB). In STM-induced reactions, IBB shows concerted activation of both halogens, which does not allow the individual addressal of one bond at a time. The concept of individual addressabilities of bonds in bi-substituted molecule was confirmed by use of BPN. This reactant is, however, strongly bound to the substrate and, hence, not very suitable for the assembly of larger aggregates, even if the nitrile group could be activated. We found individual activation of one of the bromines of DBB. This molecule lies flat on the surface and it is a promising candidate for the assembly of larger molecular aggregates, if ever future research will address STM-based molecular assembly. In order for STM-based assembly of molecular structures ever to become useful, the rigid attachment of the resultant product molecules to the substrate is a requirement. Unsubstituted aryls are mobile on Cu surfaces even at liquid nitrogen temperatures. In many molectronic schemes aromatic thiols have shown good substrate attachment at sufficient electrical conductivity even at ambient temperatures. We investigated the possibility of depositing aromatic thiols on Cu(111) at low enough temperature, so that the thiolates is not formed spontaneously. Subsequently, we could form the thiol substrate bonds at will on molecules that were located at desired surface location. We also identified effects of surface induced chirality on the adsorption behavior of such molecules. In summary, during this two-years project a molecule suitable for controlled intermolecular attachment was identified. The deposition of the molecules was optimized and a route to proven substrate attachment was established