Electrochemical syntheses and self assembly of nanostructure as modified electrodes for polythiophene preparation

ELECTROCHEMICAL SYNTHESES AND SELF-ASSEMBLY OF NANOSTRUCTURE AS MODIFIED ELECTRODES FOR POLYTHIOPHENE PREPARATION ZHANG CHUNYAN NATIONAL UNIVERSITY OF SINGAPORE 2002 ELECTROCHEMICAL SYNTHESES AND SELF-ASSEMBLY OF NANOSTRUCTURE AS MODIFIED ELECTRODES FOR POLYTHIOPHENE PREPARATION ZHANG CHUNYAN (B. Sc. Nanjing University of P. R. China) A THESIS SUBMITTED FOR DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2002 i Acknowledgments I would like to express my greatest appreciation to my supervisors, Professor Hardy, S. O. Chan and Associate Professor Ng Siu Choon for providing this opportunity for my academic pursuit and for their great help and valuable guidance throughout the years. My heartfelt thanks must go to all the colleagues in the Functional Polymer Laboratory, NUS for their continuous help and encouragement. Special thanks to Dr. Miao Ping and Dr. Richard, Seow Swee How for their kindness in providing bithiophene derivatives for my research and their valuable advice, Dr. Chen Zhikuan, Dr. Dou Zeling, Han Yanhui and Fu Ping for their assistance in lab life, Ong Teng Teng, Xu Lingge, Chen Dizhong, Sun Tong, Xu Jinmei, Lu Hongfang, Ma Yifei, Wong Yeong Ching and many others for their help and accompany. I would also like to thank the sta® of Central Instrumental Lab, Chemical Store in Chemistry Department for their assistance during this project. Many thanks to Physics Department, Material Science Department and Biology Department in using AFM, SEM and TEM instruments. Special thanks to Mr. Wong How Kwong from Physics Department for doing the XPS analysis. Finally, I wish to express my gratitude to my parents for their constant caring ii and support throughout my life. Special thanks go to my husband Zou Yu for his support and help in my thesis editing. Zhang Chunyan 2002 iii Contents Acknowledgments Contents i iii List of Figures x List of Tables xix Abbreviations xxi Summary xxiv Chapter 1. Introduction 1.1 Introduction to Conducting Polymers . . . . . . . . . . . . . . . . 1.2 Conduction Mechanism . . . . . . . . . . . . . . . . . . . . . . . . 1.2.1 Band Theory . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.2 Polaron and Bipolaron Model . . . . . . . . . . . . . . . . 1.2.3 Conductivity of Conducting Polymers . . . . . . . . . . . . 1.3 Chemistry of Polythiophenes . . . . . . . . . . . . . . . . . . . . . 1.3.1 Functionalization of Polythiophenes . . . . . . . . . . . . . 1.3.2 Chemical Syntheses of Polythiophenes . . . . . . . . . . . 10 1.3.3 Electrochemical Syntheses of Polythiophenes . . . . . . . . 10 1.3.4 Factors in Electrochemical Polymerization . . . . . . . . . 12 1.4 Properties of Polythiophenes . . . . . . . . . . . . . . . . . . . . . 13 1.4.1 Electrochemical Properties of Polythiophenes . . . . . . . 13 iv 1.4.2 Spectroscopic Properties of Polythiophenes - UV-vis-NIR Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.3 16 Chemical Environment of Elements - X-ray Photoelectron Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.5 Self-assembly of Polythiophenes . . . . . . . . . . . . . . . . . . . 19 1.6 A Bridge: Conducting Polymers and Metal Nanoparticles . . . . . 21 1.7 An Introduction to Metal Nanoparticle . . . . . . . . . . . . . . . 22 1.7.1 Historic Perspective of Gold Nanoparticles . . . . . . . . . 22 1.7.2 Band Structure of Noble Metal Nanoparticles . . . . . . . 23 1.7.3 Stabilization Methods of Metal Nanoparticles . . . . . . . 24 1.8 Preparative Methods of Metal Nanoparticles . . . . . . . . . . . . 26 1.8.1 Solution Phase Salt Reduction . . . . . . . . . . . . . . . . 26 1.8.2 Brust's Method and It's Applications . . . . . . . . . . . . 27 1.9 Properties and Characterization of Metal Nanoparticles . . . . . . 29 1.9.1 Solubility of Metal Nanoparticles . . . . . . . . . . . . . . 31 1.9.2 Size and Shape of Nanoparticles . . . . . . . . . . . . . . . 31 1.9.3 UV-Visible Spectroscopy . . . . . . . . . . . . . . . . . . . 31 1.9.4 X-Ray Photoelectron Spectroscopy (XPS) . . . . . . . . . 34 1.9.5 Transmission Electron Microscopy (TEM) . . . . . . . . . 35 1.9.6 Atomic Force Microscopy (AFM) . . . . . . . . . . . . . . 36 1.9.7 Electrochemistry: Cyclic Voltammetry (CV) and Di®erential Pulse Voltammetry (DPV) . . . . . . . . . . . . . . . 37 1.10 Scope of Dissertation . . . . . . . . . . . . . . . . . . . . . . . . . 38 Chapter 2. Electrochemical Syntheses of Polybithiophene Derivatives Using BF3¢OEt2 as Electrolyte 41 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 v 2.2.1 Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.2.2 Determination of Monomer Oxidation potential . . . . . . 45 2.2.3 Determination of Polymer Oxidation Potential . . . . . . . 45 2.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . 45 2.3.1 Electrochemically Polymerization of Mono-substituted Bithiophenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 46 Electrochemical Polymerization of Bithiophenes with Alternate Electron-donating and Electron-withdrawing Groups 53 2.3.3 Electrochemically Polymerization of Symmetrically Di-substituted Bithiophenes . . . . . . . . . . . . . . . . . . . . . . . . . 56 2.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Chapter 3. Properties of BF3 ¢OEt2 Doped Polybithiophene Derivatives 66 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.2.1 Preparation of Polymers . . . . . . . . . . . . . . . . . . . 67 3.2.2 Ultraviolet-visible Absorption Spectroscopy . . . . . . . . . 67 3.2.3 X-ray Photoelectron Spectroscopy . . . . . . . . . . . . . . 68 3.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . 68 3.3.1 Electrochemical Analysis of Polymers . . . . . . . . . . . . 3.3.2 Electrolyte in the Electrochemical Syntheses and Electro- 68 chemical Properties of Halogen Symmetrically Disubstituted Polybithiophenes . . . . . . . . . . . . . . . . . . . . . . . 80 3.3.3 Optical Properties of Resulting Polymers . . . . . . . . . . 82 3.3.4 XPS Study of Polymers Prepared from BF3 ¢OEt2 . . . . . 88 3.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 vi Chapter 4. Thienylthiolate Modi¯ed Polycrystalline Au Electrode for Electrochemical Polymerization of Substituted Bithiophenes 95 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 4.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 4.2.1 Self-Assembled Thienylthiolate Monolayer on Polycrystalline Au Electrode . . . . . . . . . . . . . . . . . . . . . . . . . 97 Electrochemical Polymerization on Modi¯ed Electrode . . 98 4.3 Results and Discussions . . . . . . . . . . . . . . . . . . . . . . . 99 4.2.2 4.3.1 Formation of Self-Assembled Thienylthiolate Monolayer on Au Electrode . . . . . . . . . . . . . . . . . . . . . . . . . 99 4.3.2 Monolayer Characterization by XPS . . . . . . . . . . . . 100 4.3.3 Cyclic Voltammetry of Ferrocyanide on Chemisorbed Monolayer Modi¯ed Au Electrode . . . . . . . . . . . . . . . . . 102 4.3.4 Atomic Force Microscopy of Chemisorbed Monolayer . . . 103 4.3.5 Electrochemical Polymerization of Bithiophenes on Thienylthiolate Monolayer Modi¯ed Au Electrode . . . . . . . . . . 105 4.3.6 CV of Polymer-coated Electrode Rinsed by Organic Solvent 109 4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Chapter 5. Microelectrode of Self-Assembled Aqueous Au Nanoparticles on ITO Glass for Electrochemical Polymerization of Bithiophene 114 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 5.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 5.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . 116 5.3.1 Self-assembly of Aqueous Au Nanoparticles on Silanized ITO Glass Electrode . . . . . . . . . . . . . . . . . . . . . 116 vii 5.3.2 Electrochemistry of Various Modi¯ed Electrodes . . . . . . 117 5.3.3 UV-vis Spectroscopy in Characterization of Surface Modi¯cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 5.3.4 Surface Morphology of Modi¯ed Surfaces . . . . . . . . . . 121 5.3.5 XPS Study in Modi¯ed Surfaces . . . . . . . . . . . . . . . 124 5.3.6 Electrochemistry of PBT Synthesized on Various Electrodes 126 5.3.7 Spectroscopic Properties of PBT Synthesized on Various Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 5.3.8 XPS study in PBT Prepared on Modi¯ed Electrode. . . . 128 5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Chapter 6. Thienylthiolates Monolayer Protected Gold Nanoparticles 132 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 6.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 6.2.1 Syntheses of Thienylthiolates as Stabilization Ligands . . . 133 6.2.2 Preparation of Gold Nanoparticles with Stabilization Ligands134 6.3 Results and Discussions . . . . . . . . . . . . . . . . . . . . . . . 135 6.3.1 Monolayer Protected Gold Nanoparticle . . . . . . . . . . 135 6.3.2 Solubility . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 6.3.3 Particle Size and Distribution . . . . . . . . . . . . . . . . 138 6.3.4 Composition . . . . . . . . . . . . . . . . . . . . . . . . . . 144 6.3.5 Spectroscopic Properties . . . . . . . . . . . . . . . . . . . 148 6.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Chapter 7. Coulomb Staircase Feature of Thienylthiolate-Stabilized Au Nanoparticles 152 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 7.1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . 152 viii 7.1.2 Metal Nanoparticles as Building Blocks . . . . . . . . . . . 153 7.1.3 Coulomb Staircase . . . . . . . . . . . . . . . . . . . . . . 153 7.1.4 Solution Ensemble Coulomb Staircase . . . . . . . . . . . . 156 7.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 7.3 Results and Discussions . . . . . . . . . . . . . . . . . . . . . . . 159 7.3.1 CV and DPV of Thienylthiolate Stabilized Gold Nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 7.3.2 Solvent E®ect in Quantized Double Layer Charging . . . . 162 7.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Chapter 8. Electrochemical Polymerization of Bithiophenes Incorporating Thienylthiolate Stabilized Au Nanoparticles 166 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 8.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 8.3 Results and Discussions . . . . . . . . . . . . . . . . . . . . . . . 168 8.3.1 Self-assembly of Nonaqueous Au Colloid on silanized ITO Glass Electrode. . . . . . . . . . . . . . . . . . . . . . . . . 168 8.3.2 Electrochemical Polymerization of Bithiophenes in a Solution Containing Thienylthiolate Stabilized Au Nanoparticles 175 8.3.3 Properties of Polybithiophenes Incorporated with Au Nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 8.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Chapter 9. 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AFM images of (A) ITO, (B) ITOS, (C) ITOSA and (D) ITOSASBT surfaces 122 5.7 2D phase AFM images of (A) ITO, (B) ITOS, (C) ITOSA and (D) ITOSASBT surfaces 123 5.8 S(2p) spectrum of ITOSASBT surfaces 124 5.9 Au(4f) spectra of (A) ITOSA and (B) ITOSASBT surfaces 125 5.10 CVs of PBT deposited on (a) ITO, (b) ITOSA and (c) ITOSASBT in 0.1... arrangement of SSBT adsorbed on the surface of gold cluster 165 xviii 8.1 UV-vis spectra of nonaqueous gold nanoparticles (A) AUSSBT, (B) AURSBT, (C) AU3SBT and (D) Au5SBT adsorbed on silanized ITO glass electrode 169 8.2 AFM (A) 2D phase image and (B) 3D phase image of self- assembled SSBT stabilized Au nanoparticles on ITO glass 170 8.3 SEM image of self- assembled... Polaron and bipolaron structures of polythiophene S S Aromatic Quinoid Figure 1.3: Aromatic and quinoid structures of thiophene Subsequent removal of electrons generates more polarons When the numbers of polarons increase to a certain extent, two nearby polarons tend to combine and form a bipolaron as shown in Figure 1.2 Theoretical studies have shown that the formation of bipolaron via combination of polarons... NBF4 /CH3 CN at scan rate of 50 mV s¡1 112 xv 5.1 Schematic diagram of self- assembled Au nanoparticles onto silanized ITO glass electrode and subsequent self- assembly of 5SHBT molecules (A: !-aminopropyl-triethoylsilane; B: 5SHBT) 117 5.2 Voltametric response of 5.0 mM Fe(CN)4+ in 0.5 M Na2 SO4 aque6 ous solution on (a) ITO, (b) ITOSA and (c) ITOSASBT at scan rate of 50 mV s¡1 ... which is of great interest in both fundamental research and potential application as a nano transistor Different solvents show in°uence in the quantized double layer capacitance of gold core The techniques employed were mainly electrochemical analysis, TEM and XPS xxvi Electrochemical polymerization of bithiophenes were carried out on gold nanoparticle modi¯ed ITO glass electrode through self- assembly. .. molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is known as bandgap energy (Eg ) As shown in Figure 1.1, for metals, the VB and CB are overlapped and the intrinsic conductivity is attributed to the nonexistence of bandgap For semiconductors, the narrow bandgap energy enables electrons be promoted to the CB by thermal excitation at room temperature and the materials become... TEM and (B) AFM height images of AUSSBT nanoparticles 140 6.4 (A) TEM and (B) AFM height images of AURSBT nanoparticles 141 6.5 (A) TEM and (B) AFM height images of AU5SBT nanoparticles 142 6.6 (A) TEM and (B) AFM height images of AU3SBT nanoparticles 142 6.7 TEM Images of AUBRSBT nanoparticles with a surfactant-metal feeding ratio of (A) 1:1, (b) 1:2, (C) 2:1 and (D) 5:1 143 6.8 XPS spectra of. .. Syntheses 191 10.3.1 Preparation of Thienyl Thiols 191 10.3.2 Electrochemical Polymerization 194 10.3.3 Preparation of Colloidal Gold Nanoparticles 194 10.3.4 Electrode Modi¯cation 195 Bibliography 197 x List of Figures 1.1 Illustration of energy band structures of materials VB: valence band, CB: conduction band... derivatives are often considered as a model system for the studies of conducting polymers with non-degenerate ground states [27, 28, 29, 30, 31, 32, 33] 8 1.3.1 Functionalization of Polythiophenes In addition to their good environmental stability and original electronic structure with moderate bandgap, structural versatility of thiophene-based polymers has drawn continuous interest in the research of conducting . ELECTROCHEMICALSYNTHESESAND SELF-ASSEMBLYOFNANOSTRUCTUREAS MODIFIEDELECTRODESFORPOLYTHIOPHENE PREPARATION ZHANGCHUNYAN NATIONALUNIVERSITYOFSINGAPORE 2002 ELECTROCHEMICALSYNTHESESAND SELF-ASSEMBLYOFNANOSTRUCTUREAS MODIFIEDELECTRODESFORPOLYTHIOPHENE PREPARATION ZHANGCHUNYAN (B.Sc.NanjingUniversityofP.R.China) ATHESISSUBMITTED FORDOCTOROFPHILOSOPHY DEPARTMENTOFCHEMISTRY NATIONALUNIVERSITYOFSINGAPORE 2002 i Acknowledgments Iwouldliketoexpressmygreatestappreciationtomysupervisors,Professor Hardy,S.O.ChanandAssociateProfessorNgSiuChoonforprovidingthisop- portunityformyacademicpursuitandfortheirgreathelpandvaluableguidance throughouttheyears. MyheartfeltthanksmustgotoallthecolleaguesintheFunctionalPolymer Laboratory,NUSfortheircontinuoushelpandencouragement.Specialthanksto Dr.MiaoPingandDr.Richard,SeowSweeHowfortheirkindnessinproviding bithiophenederivativesformyresearchandtheirvaluableadvice,Dr.Chen Zhikuan,Dr.DouZeling,HanYanhuiandFuPingfortheirassistanceinlablife, OngTengTeng,XuLingge,ChenDizhong,SunTong,XuJinmei,LuHongfang, MaYifei,WongYeongChingandmanyothersfortheirhelpandaccompany. Iwouldalsoliketothankthesta®ofCentralInstrumentalLab,ChemicalStore inChemistryDepartmentfortheirassistanceduringthisproject.Manythanks toPhysicsDepartment,MaterialScienceDepartmentandBiologyDepartment inusingAFM,SEMandTEMinstruments.SpecialthankstoMr.WongHow KwongfromPhysicsDepartmentfordoingtheXPSanalysis. Finally,Iwishtoexpressmygratitudetomyparentsfortheirconstantcaring ii andsupportthroughoutmylife.SpecialthanksgotomyhusbandZouYufor hissupportandhelpinmythesisediting. ZhangChunyan 2002 iii Contents Acknowledgmentsi Contentsiii ListofFiguresx ListofTablesxix Abbreviationsxxi Summaryxxiv Chapter1.Introduction1 1.1IntroductiontoConductingPolymers. ELECTROCHEMICALSYNTHESESAND SELF-ASSEMBLYOFNANOSTRUCTUREAS MODIFIEDELECTRODESFORPOLYTHIOPHENE PREPARATION ZHANGCHUNYAN NATIONALUNIVERSITYOFSINGAPORE 2002 ELECTROCHEMICALSYNTHESESAND SELF-ASSEMBLYOFNANOSTRUCTUREAS MODIFIEDELECTRODESFORPOLYTHIOPHENE PREPARATION ZHANGCHUNYAN (B.Sc.NanjingUniversityofP.R.China) ATHESISSUBMITTED FORDOCTOROFPHILOSOPHY DEPARTMENTOFCHEMISTRY NATIONALUNIVERSITYOFSINGAPORE 2002 i Acknowledgments Iwouldliketoexpressmygreatestappreciationtomysupervisors,Professor Hardy,S.O.ChanandAssociateProfessorNgSiuChoonforprovidingthisop- portunityformyacademicpursuitandfortheirgreathelpandvaluableguidance throughouttheyears. MyheartfeltthanksmustgotoallthecolleaguesintheFunctionalPolymer Laboratory,NUSfortheircontinuoushelpandencouragement.Specialthanksto Dr.MiaoPingandDr.Richard,SeowSweeHowfortheirkindnessinproviding bithiophenederivativesformyresearchandtheirvaluableadvice,Dr.Chen Zhikuan,Dr.DouZeling,HanYanhuiandFuPingfortheirassistanceinlablife, OngTengTeng,XuLingge,ChenDizhong,SunTong,XuJinmei,LuHongfang, MaYifei,WongYeongChingandmanyothersfortheirhelpandaccompany. Iwouldalsoliketothankthesta®ofCentralInstrumentalLab,ChemicalStore inChemistryDepartmentfortheirassistanceduringthisproject.Manythanks toPhysicsDepartment,MaterialScienceDepartmentandBiologyDepartment inusingAFM,SEMandTEMinstruments.SpecialthankstoMr.WongHow KwongfromPhysicsDepartmentfordoingtheXPSanalysis. Finally,Iwishtoexpressmygratitudetomyparentsfortheirconstantcaring ii andsupportthroughoutmylife.SpecialthanksgotomyhusbandZouYufor hissupportandhelpinmythesisediting. ZhangChunyan 2002 iii Contents Acknowledgmentsi Contentsiii ListofFiguresx ListofTablesxix Abbreviationsxxi Summaryxxiv Chapter1.Introduction1 1.1IntroductiontoConductingPolymers. 121 5.62DheightAFMimagesof(A)ITO,(B)ITOS,(C)ITOSAand (D)ITOSASBTsurfaces 122 5.72DphaseAFMimagesof(A)ITO,(B)ITOS,(C)ITOSAand(D) ITOSASBTsurfaces 123 5.8S(2p)spectrumofITOSASBTsurfaces 124 5.9Au(4f)spectraof(A)ITOSAand(B)ITOSASBTsurfaces