Study Of Cyanogroup Modified Conjugated Molecular Assembly Structure And Polymerization Reaction On Surface

Self-assembled structures and polymerization reactions of cyanogroup modified conjugated molecules on metal surface have been investigated by the combination of scanning tunneling microscopy(STM) and X-ray photoelectron spectroscopy(XPS). STM observations clearly demonstrate that cyanides form ordered self-assembled double-hydrogen bond structures on silver surface and further reveal that the opposite double hydrogen bond formed among 1,2,4,5-TCNB molecules is much more stable than the neighboring double hydrogen bond among 2,3-DCN molecules. For the first time, conjugated AgPc-type and AuPc-type polymers have been successfully synthesized by 2,9-dihydrodibenzo [fg, op] tetracene-5,6,12,13-tetracarbonirile via cyclization reaction on noble metal Ag(111) and Au(111) surface without the introduction of any type guest metal atoms. Moreover, such conjugated polymers can further aggregate to 1D chain or 2D mesh polymers with the increase of the annealing temperature. Various stages in this kind of cyclization reaction process have been directly observed by STM at molecular level. It is found that at the initial stage, the Au adatoms are connected with the cyanogroups of 2,9-dihydrodibenzo [fg, op] tetracene-5,6,12,13-tetracarbonirile(BTTN) molecules to form the ordered left-handed alternated with right-handed metal coordinate structures, secondly, this mixed structure gradually converts to the left-handed or right-handed metal coordinate structure with the increase of the annealing temperature, finally the surface-assistanted cyclization reaction takes place to form the conjugated polymer of AuPc-type. The introduction of Br atoms to the molecular structure causes two kind of chemical reactions: under the low molecular packing density, the cyanogroup cyclization reaction takes place and the molecules are synthesized to metal-Pc type polymers; under high molecular packing density, Ullmann reaction is dominant and then the molecules are successfully synthesized to ordered conjugated molecular chains. In addition, the steric-hinerance effect derived from the tertiary butyl of 2,9-di tert-butyldibenzo [fg, op] tetracene-5,6,12,13-tetracarbonirile effectively prevents the cyanogroup polymerization reaction.