Synthesis Of One-dimensional Conjugated Polymer Chains Based On Porphyrin Molecules

One of the major goals of the "bottom-up" nanotechnology is to build molecular electronic devices,that is,the working components are based on molecules.For molecular electronic devices,the molecular components should be covalently connected to allow a considerable carrier transport.Conducting molecular wire is an important part to build a molecular device.The synthesis of one-dimensional conjugated polymer chains is of great significance to achieve molecular wires which are suitable for carrier transport.In this dissertation,The formation of various molecular wires with different molecule precursors(including 4,4?-dibromo-p-terphenyl(DBTP),porphine(H-P),5,15-(di-4-ethynylphenyl)porphyrin(DEPP),5,15-(dimesityl)porphyrin(DMP))on metal substrates(including Cu(110),Ag(110))have been systematically studied.The main achievements in this dissertation are presented as below:1.One-dimensional conjugated polymer chains were synthesized on Cu(110)and Ag(110)surface via Ullman coupling reaction of 4,4?-dibromo-p-terphenyl(DBTP)molecules.Scanning tunneling microscopy(STM)observations show that the gradual thermal excitation can induce the convertion of 1D organometallic chains into 1D conjugated polymer chains on all the metal surfaces.In addition,the formation of 1D ladder-shaped conjugated polymer chains has been observed through the direct carbon-carbon coupling of the DBTP molecules at the meta-C sites.2.The influence of metal surfaces on the formation of 1D molculear chains via polymerization of porphine(H-P)molecules have been studied by STM.Porphine(H-P)molecules are firstly deposited on metal surface at 300 K,and then undergo gradual annealing.On Cu(110)surface,Cu atoms are involved into the coupling reaction to form 1D linear organometallic chains via C-Cu-C bonds.Further annealing drives these 1D organometallic chains to conjugate into two-dimensional mesh-like structures.In constrast,the polymerization reaction of the H-P molecules on Ag(110)surface is dominated by carbon-carbon coupling process so that areconjugated polymers are formed.While the coverage of molecular is very high,1D linear short conjugated polymer chains are formed.3.The reaction pathes of the terminal alkyne group on metal surfaces have been studied at the molecular level.On Cu(110)surface,DEPP molecules have been transformed into a polymer chain via thermal treatment when the alkyne groups of DEPP molecules are cracked due to the high surface activity of Cu(110)surface.On Ag(110)surface,vapor deposition of DEPP molecules leads to the formation of self-assembly structure with mixture of DEPP and Ag atoms.Thermal annealing causes the alkyne groups to bond to the Ag atoms,so 1D stable linear organometallic chains have been formed.4.The dependence of the reaction ways of the terminal mesityl groups within5,15-(dimesityl)porphyrin(DMP)molecules on the type of metal surfaces have been investigated by STM.While the DMP molecules aggregate into 1D linear molecular chains due to the interactions of the CH-? bonds,the such 1D molecular chains disappeared with the increasing of the annealing temperature,as a consequence,disordered polymers are left on Ag(110)surface.In contrast,the deposition of DMP molecules on Cu(110)at 300 K leads to the formation of non covalent self-assembly structure.Annealing at 423 K induces DMP molecules to form 1D conjugated polymer chains.This kind of polymerization reaction involves dehydrogenation homocoupling and cyclodehydrogenation,while the reaction sites include methyl,phenyl CH,porphyrin ?CH.Individual and continuous carbon-carbon coupling of DMP molecules are achieved ultimately,in which the latter leads to the formation of2~3 new aromatic rings at molecular junction.