Fabrication And Electrochemical Characterization Of The SAMs Of Various Molecular Wires

Molecular self-assembly provides an ideal technology for the precise control of interfacial properties and surface structure at molecular level,which provides a useful mean for studying many fundamental issues such as electron transfer through interfaces,molecular interaction and interfacial structure-property relations.This thesis studies the self-assembly properties of a series of linear conjugated molecules and explored their potential application in the fields of molecular electronics and chemical sensors.Firstly,the thin film morphologies of a series of dendrimer modified OPE molecular wires on mica surface were investigated and the relation between film morphologies and molecular structure was discussed.Secondly,the electrochemical and spectroscopic properties of a series of diferrocene derivatives were studied.It was found that these molecules exhibit high selective bind with Zn²⁺ cations and could be applied as novel multifunctional chemical sensors.At the last, the self-assembly and electron transfer behavior or a series of ferrocene containing linear aromatic molecules were investigated by electrochemical methods.This thesis is consisted of five parts as the following:Chapter 1:IntroductionThe literature review on the molecular self-assembly is provided,which covers the history,the structural characteristics and properties of self-assembled monolayer (SAMs) and its applications in many fields.Chapter 2:Experimental method and technologyAn introduction is given to the characterization techniques employed in this study and the key instruments involved.Chapter 3:Preparation of thin films from "core-shell" molecular wires and the film morphology controlThin films of series of "core-shell" molecules were fabricated on mica surface by drop casting and their morphologies were studied by atomic force microscope(AFM). For the first,we reported on how the film nanostructures were influenced by the generation of the dendrimer "shells" of the molecules.In addition,the effects of substrate,solvents and solution concentrations have been investigated to find the optimal condition for film fabrication.Chapter 4:Preparation and characterization of SAMs of "core-shell" molecular wires on gold surfaceSAMs of a series of "core-shell" molecular wires were prepared on gold electrode surface via a potential assisted self-assembly method.The SAMs were characterized by XPS,cyelovoltametry and AC impedance analysis.It was found that the molecular packing density decreases with the increase of dendrimer side chains.Chapter 5:Interfacial electron transfer though a series of ferrocene containing molecular wiresA series of ferrocenylthiol compounds with different conjugated framework were designed and synthesized.The self-assembled monolayers(SAMs) of these molecular wires were prepared on gold electrodes and were characterized by electrochemistry and XPS.The interracial electron transferring process in such monolayers were studied by de cyclic voltammetry.Chapter 6:Ion sensing properties of a series of diferrocene compoundsThree linear diferrocene derivatives has been designed and synthesized,which consist of ferrocene(Fc) groups and different conjugated frameworks linked via imine bonds.All the three compunds show highly specific binding with Zn2+ cation and exhibit significant electrochemical and optical response after forming the dimmer complexes.Our results indicate that the conjugation degree of the frameworks has very weak influence on the electrochemical properties.However,the high conjugation degree is beneficial for the spectroscopic responses,including large red shift in electronic spectra and higher fluorescence intensity.Meanwhile,these molecules exhibit interesting ability to reversibly catch and release Zn²⁺ upon solvent change, which may be potentially applied to release Zn²⁺ containing medicines in bio-system. From the fundamental aspect,it is demonstrated that connecting two ferrocene subunits by conjugated "bridges" with cation-binding sites is an attractive strategy for designing new redox-active chemosensors.This work provides useful information for further design and optimization of multifunctional ion sensing materials.Chapter 7:Electrochemical assisted assembly of ferrocene on electrode surface for mediating the heterogeneous electron transfer of Cyt CFerrocene(Fc) containing monolayer were successfully prepared on gold electrode surface using an electrochemical assisted assembly method.The obtained monolayer possesses the shortest separation between the immobilized Fc moieties and the electrode surface.The Fc monolayer could be used as electrochemical media for the heterogeneous electron transfer from Cyt C to the gold electrode.