Edited by

Mohamed Mehdi Chehimi

Aryl Diazonium Salts

Related Titles

Pinna, N., Knez, M. (eds.)

Atomic Layer Deposition of Nanostructured Materials

2011

ISBN: 978-3-527-32797-3

Mittal, V. (ed.)

Surface Modification of Nanotube Fillers

2011

ISBN: 978-3-527-32878-9

del Campo, A., Arzt, E. (eds.)

Generating Micro- and Nanopatterns on Polymeric Materials

2011

ISBN: 978-3-527-32508-5

Xanthos, M. (ed.)

Functional Fillers for Plastics

2010

ISBN: 978-3-527-32361-6

Patai, S.

Patai Chemistry of Diazonium and Diazo Groups, Part 1 and 2

Online Book Wiley Interscience

ISBN: 978-0-470-77154-9 (Part 1)

ISBN: 978-0-470-77155-6 (Part 2)

Scott, P. (ed.)

Linker Strategies in Solid-Phase Organic Synthesis

ISBN: 978-0-470-51116-9

Basset, J.-M., Psaro, R., Roberto, D., Ugo, R. (eds.)

Modern Surface Organometallic Chemistry

2009

ISBN: 978-3-527-31972-5

Förch, R., Schönherr, H., Jenkins, A. T. A. (eds.)

Surface Design: Applications in Bioscience and Nanotechnology

2009

ISBN: 978-3-527-40789-7

Bhattacharya, A., Rawlins, J. W., Ray, P. (eds.)

Polymer Grafting and Crosslinking

ISBN: 978-0-470-40465-2

Electrochemical Surface ModificationThin Films, Functionalization and Characterization

Series: Advances in Electrochemical Sciences

and Engineering (Volume 10)

Series edited by Alkire, R. C., Kolb, D. M.,

Lipkowski, J., and Ross, P.

2008

ISBN: 978-3-527-31419-5

Aryl Diazonium Salts

New Coupling Agents in Polymer and Surface Science

Edited by Mohamed Mehdi Chehimi

The Editor

Dr. Mohamed Mehdi ChehimiUniversity Paris DiderotSorbonne Paris CitéITODYSUMR CNRS 708615 rue J-A de Baïf75013 ParisFrance

All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

Library of Congress Card No.: applied for

British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.

Bibliographic information published by the Deutsche NationalbibliothekThe Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at <http://dnb.d-nb.de>.

© 2012 Wiley-VCH Verlag & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN:    978-3-527-32998-4ePDF ISBN:   978-3-527-65047-7ePub ISBN:    978-3-527-65046-0mobi ISBN:    978-3-527-65045-3oBook ISBN:  978-3-527-65044-6

Cover Design  Adam-Design, WeinheimTypesetting  Toppan Best-set Premedia Limited, Hong KongPrinting and Binding  Markono Print Media Pte Ltd, Singapore

V

To Jean Pinson, with gratitude

VII

Contents

1 AttachmentofOrganicLayerstoMaterialsSurfacesbyReductionofDiazoniumSalts  1

JeanPinson1.1  A Brief Survey of the Chemistry and Electrochemistry  

of Diazonium Salts  11.2  The Different Methods that Permit Grafting of Diazonium Salts  31.2.1  Electrochemistry  31.2.2  Reducing Substrate, Homolytic Dediazonation,  

Reaction with the Substrate  41.2.3  Reducing Reagent  51.2.4  Neutral and Basic Media  61.2.5  Ultrasonication  61.2.6  Heating and Microwave  61.2.7  Mechanical Grafting  71.2.8  Photochemistry  71.3  The Different Substrates, Diazonium Salts, and Solvents  

that Can Be Used  71.3.1  Substrates  71.3.2  Diazonium Salts  91.3.3  Solvents  101.4  Evidence for the Presence of a Bond between the Substrate  

and the Organic Layer  111.4.1  Stability of the Layer  111.4.2  Spectroscopic Evidence for a Bond  121.5  From Monolayers to Multilayers  131.5.1  Monolayers  141.5.2  Layers of Medium Thickness  161.5.2.1  Thick Layers  191.6  Structure and Formation of Multilayers  21

Preface XV ListofContributors XVII

VIII Contents

1.6.1  Chemical Structure  211.6.2  The Spatial Structure of the Layers  221.6.3  Compactness of the Layers  231.6.4  Swelling of the Layer  241.6.5  Electron Transfer through the Layers  241.6.6  The Formation Mechanism of Multilayers  251.7  Conclusion  27 References  27

2 Aryl–SurfaceBonding:ADensityFunctionalTheory(DFT)SimulationApproach  37

NanShao,ShengDai,andDe-enJiang2.1  Introduction  372.2  Density Functional Theory  382.3  Bonding between Aryl and Various Substrates  382.3.1  On Graphite/Graphene  392.3.1.1  On the Basal Plane  392.3.1.2  On the Edges of Graphene  422.3.2  On Carbon Nanotubes  442.3.3  On Metal Surfaces  452.4  Summary and Outlook  48  Acknowledgments  49 References  50

3 PatternedMolecularLayersonSurfaces  53 AlisonJ.Downard,AndrewJ.Gross,andBradleyM.Simons3.1  Methods Based on Scanning Probe Lithography  533.1.1  AFM  543.1.2  SECM  543.1.3  Spotting  563.2  Methods Based on Soft Lithography  573.2.1  Printing  573.2.2  Molds  593.2.3  Nanosphere Lithography  593.3  Methods Based on Lithography  603.4  Methods Based on Surface-Directed Patterning  623.4.1  Modification of Si Surfaces  633.4.2  Modified Electrode Arrays  643.5  Summary and Conclusions  66 References  68

4 AnalyticalMethodsfortheCharacterizationofArylLayers  71 KarstenHinrichs,KatyRoodenko,JörgRappich,

MohamedM.Chehimi,andJeanPinson4.1  Introduction  714.2  Scanning Probe Microscopies  71

Contents IX

4.3  UV–VIS Spectroscopy: Transmission, Reflection,  and Ellipsometry  72

4.4  IR Spectroscopy  724.4.1  Transmission Spectroscopy  734.4.2  Reflection Spectroscopy  744.4.3  Infrared Spectroscopic Ellipsometry (IRSE)  754.4.4  IRSE Surface Characterization  774.4.5  InSitu IR Spectroscopy: ATR and IRSE  794.5  Raman Spectroscopy and Surface-Enhanced Raman  

Scattering (SERS)  834.6  X-ray Photoelectron Spectroscopy (XPS)  844.7  X-ray Standing Waves (XSW)  914.8  Rutherford Backscattering  934.9  Time of Flight Secondary Ion Mass Spectroscopy  934.10  Electrochemistry  944.11  Contact Angle Measurements  964.12  Conclusion  96 References  98

5 ModificationofNano-objectsbyArylDiazoniumSalts  103

Dao-JunGuoandFakhradinMirkhalaf5.1  Introduction  1035.2  Electrochemical Modification of Nano-objects  

by Reduction of Diazonium Salts  1055.2.1  Surface Modification of Carbon Nano-objects via Electrochemical 

Reduction of Aryl Diazonium Cations  1055.2.2  Surface Modification of Metal and Metal Oxide Nano-objects via 

Electrochemical Reduction of Aryl Diazonium Cations  1115.3  Chemical Modification of Nano-objects by Reduction  

of Diazonium Salts  1125.3.1  Surface Modification of Carbon Nano-objects via Chemical Reduction  

of Aryl Diazonium Cations  1125.3.2  Surface Modification of Metal and Metal Oxide Nano-objects via 

Chemical Reduction of Aryl Diazonium Cations  1165.4  Summary and Conclusions  119  Acknowledgments  120 References  120

6 PolymerGraftingtoArylDiazonium-ModifiedMaterials:MethodsandApplications  125

SarraGam-Derouich,SamiaMahouche-Chergui,HatemBenRomdhane,andMohamedM.Chehimi

6.1  Introduction  1256.2  Methods for Grafting Coupling Agents from Aryl Diazonium 

Compounds  127

X Contents

6.3  Grafting Macromolecules to Surfaces through Aryl Layers  1306.3.1  Binding Macromolecules to Surfaces by a Grafting  

from Strategy  1306.3.1.1  Surface-Initiated Atom Transfer Radical Polymerization  

(SI-ATRP)  1306.3.1.2  Surface-Initiated Reversible Addition–Fragmentation  

Chain Transfer (SI-RAFT)  1426.3.1.3  Surface-Initiated Photopolymerization  1436.3.1.4  Alternative Methods  1466.3.2  Attachment of Macromolecules through Grafting  

onto Strategies  1476.3.2.1  Photochemical Attachment  1476.3.2.2  Ring Opening  1486.3.2.3  Acylation  1496.3.2.4  Click Chemistry  1496.3.2.5  Diazotation of Substrates and Macromolecules  1506.4  Adhesion of Polymers to Surfaces through Aryl Layers  1516.5  Conclusion  153 References  153

7 GraftingPolymerFilmsontoMaterialSurfaces:TheOne-StepRedoxProcesses  159

GuyDeniau,SergePalacin,AliceMesnage,andLorraineTessier7.1  Cathodic Electrografting (CE) in an Organic Medium  1607.1.1  Direct Cathodic Electrografting of Vinylic Polymers  1607.1.2  Indirect Cathodic Electrografting  1627.2  Surface Electroinitiated Emulsion Polymerization (SEEP)  1647.2.1  Characterization of Poly(Butyl Methacrylate) Films  1667.2.2  Determination of the Film Structure  1677.2.3  Reduction of Protons and the Role of Hydrogen Radicals  1697.2.4  Mechanism of SEEP  1707.3  Chemical Grafting via Chemical Redox Activation (Graftfast™)  1717.3.1  Process without Vinylic Monomer  1727.3.2  Process with Vinylic Monomer  1747.3.2.1  Type of Materials  1747.3.2.2  Parameters Controlled in the Process  1747.4  Summary and Conclusions  177 References  178

8 ElectrograftingofConductiveOligomersandPolymers  181

JeanChristopheLacroix,JalalGhilane,LuisSantos,GaelleTrippe-Allard,PascalMartin,andHyacintheRandriamahazaka

8.1  Introduction  1818.2  Conjugated Oligomers and Polymers  181

Contents XI

8.3  Surface Grafting Based on Electroreduction  of Diazonium Salts  184

8.4  Polyphenylene and Oligophenylene-Tethered Surface Prepared by the Diazonium Reduction of Aniline or 4-Substituted Aniline  187

8.5  n-Doping and Conductance Switching of Grafted Biphenyl, Terphenyl, Nitro-biphenyl and 4-Nitroazobenzene Mono- and Multilayers  187

8.6  p-Doping and Conductance Switching of Grafted Oligo-Phenylthiophene or Oligothiophene Mono- and Multilayers  190

8.7  p-Doping and Conductance Switching of Grafted Oligoaniline Mono- and Multilayers  192

8.8  Conclusion and Outlook  193 References  195

9 TheUseofArylDiazoniumSaltsintheFabricationofBiosensorsandChemicalSensors  197

J.JustinGooding,GuozhenLiu,andAliciaL.Gui9.1  Introduction  1979.1.1  Sensors and Interfacial Design  1979.1.2  Molecular Level Control over the Fabrication  

of Sensing Interfaces  1989.2  The Important Features of Aryl Diazonium Salts  

with Regard to Sensing  2009.3  Sensors and Biosensors Fabricated Using Aryl  

Diazonium Salts  2019.3.1  Chemical Sensors – Sensors Fabricated via the Immobilization  

of Chemical Recognition Species  2019.3.2  Biosensors  2059.3.2.1  Enzyme Biosensors  2069.3.2.2  Immunobiosensors  2089.3.2.3  DNA-Based Biosensors  2109.3.2.4  Cell-Based Biosensors  2139.4  Conclusions  213 References  214

10 DiazoniumCompoundsinMolecularElectronics  219 RichardMcCreeryandAdamJohanBergren10.1  Introduction  21910.2  Fabrication of Molecular Junctions Using Diazonium Reagents  22210.2.1  Substrates for Diazonium-Derived Molecular Junctions  22210.2.2  Surface Modification Using Diazonium Chemistry  22310.2.3  Application of Top Contacts  22510.3  Electronic Performance of Diazonium-Derived  

Molecular Junctions  22610.3.1  Surface Diffusion Mediated Deposition (SDMD)  22710.3.2  Structural Control of Molecular Junction Behavior  230

XII Contents

10.3.3  Redox Reactions in Molecular Junctions  23210.3.4  Microfabricated Molecular Devices Made  

with Diazonium Chemistry  23310.4  Summary and Outlook  235  Acknowledgments  236 References  236

11 ElectronicPropertiesofSiSurfacesModifiedbyArylDiazoniumCompounds  241

JörgRappich,XinZhang,andKarstenHinrichs11.1  Introduction  24111.2  Experimental Techniques to Characterize Electronic Properties  

of Si Surfaces in Solutions  24211.2.1  InSitu Photoluminescence and Photo Voltage Measurements  24211.2.2  InSitu PL and PV Measurements during 

Electrochemical Grafting  24411.2.3  Reaction Scheme of the Electrochemical Grafting via  

Diazonium Ions  24511.2.4  Change in IPL and UPV during Electrochemical Grafting 

onto Si Surfaces  24611.2.5  Change in Band Bending and Work Function after  

Electrochemical Grafting onto Si Surfaces  24811.2.6  pH Dependence and Enhanced Surface Passivation  24911.3  Conclusion and Outlook  251  Acknowledgments  252 References  252

12 Non-DiazoniumOrganicandOrganometallicCouplingAgentsforSurfaceModification  255

FetahI.Podvorica12.1  Amines  25512.1.1  Characterization of the Grafted Layer  25712.1.1.1  Electrochemical Methods  25712.1.1.2  Surface Analysis Techniques  25812.1.2  Chemical Grafting  25912.1.3  Localized Electrografting  26012.1.4  Grafting Mechanism  26112.1.5  Applications  26212.2  Arylhydrazines  26412.3  Aryltriazenes  26612.4  Alcohols  26712.4.1  Observation and Characterization of the Film  26812.4.2  Applications  26912.5  Grignard Reagents  27012.5.1  Characterization of the Layers  27112.5.2  Grafting Mechanism  272

Contents XIII

12.6  Onium Salts  27212.6.1  Iodonium Salts  27212.6.2  Sulfonium Salts  27312.6.3  Ammonium Salts  27312.7  Alkyl Halides  27412.8  Conclusion  275 References  276

13 VariousElectrochemicalStrategiesforGraftingElectronicFunctionalMoleculestoSilicon  283

DineshK.Aswal,ShankarPrasadKoiry,andShivKumarGupta13.1  Introduction  28313.2  Architecture of Hybrid Devices  28413.2.1  Molecular Dielectrics and Wires  28513.2.2  Molecular Diodes  28613.2.3  Resonant Tunnel Diodes  28613.2.4  Molecular Transistors  28613.3  Electrografting of Monolayers to Si  28713.3.1  Essential Requirements  28713.3.2  Experimental Process of Electrografting  28713.4  Negative Differential Resistance Effect in a Monolayer  

Electrografted Using a Diazonium Complex  28813.4.1  Electrografting of DHTT  28813.4.2  NDR Effect in DHTT Monolayers  29013.5  Dielectric Monolayers Electrografted Using Silanes  29313.5.1  Mechanism of Electrografting  29313.5.2  Electrical Characterization  29413.6  Molecular Diodes Based on C60/Porphyrin-Derivative Bilayers  29513.6.1  Fabrication Process  29613.6.1.1  Electrografting of Acceptor C60 Layer on Si  29613.6.1.2  Self-Assembly of Donor Porphyrin Derivative Layer on C60/Si  29713.6.2  Rectification Characteristics of D–A Bilayers  29813.7  Memory Effect in TPP-C11 Monolayers Electrografted  

Using a C=C Linker  30113.7.1  Electrografting of TPP-C11 Monolayer  30113.7.2  Electrical Bistability and Memory Effect  30313.8  Summary  305 References  305

14 PatentsandIndustrialApplicationsofArylDiazoniumSaltsandOtherCouplingAgents  309

JamesA.Belmont,ChristopheBureau,MohamedM.Chehimi,SarraGam-Derouich,andJeanPinson

14.1  Introduction  30914.2  Patents  30914.2.1  The Surface Chemistry of Diazonium Salts  309

XIV Contents

14.2.2  The Surface Chemistry of Other Coupling Agents  31014.2.3  Post-Modification of the Grafted Layers  31014.2.4  Composite Materials  31014.2.5  The Surface Modification of Nano-objects  31214.2.6  Microelectronics  31214.2.7  Biomedical Applications  31214.2.8  Sensors, Biosensors, Surfaces for Biological Applications  31214.2.9  Energy Conversion  31314.3  Industrial Applications  31314.3.1  The Development of Modified Carbon Blacks  31314.3.2  Industrial Applications of the Electropolymerization of Vinylics: 

Alchimer and AlchiMedics  31414.3.2.1  From Research to Development  31414.3.2.2  Application of eG™ to Drug-Eluting Stents: AlchiMedics  31514.3.2.3  Application of eG™ to Copper Interconnects: Alchimer  31714.4  Conclusion  319 References  319

Index 323

XV

Preface

Dear Reader,The diazotation of compounds has first been described in the mid-19th century

by the German chemist Peter Griess. Henceforth, aryl diazonium salts (from the French “diazote”, two nitrogen atoms) are commonly used for the synthesis of a large series of organic compounds such as azo dyes, and are thus the object of numerous articles and book chapters or sections. However, the study of the surface and interface chemistry of these salts remained sparse despite its interest in modi-fying materials surfaces. For example, it was shown in 1958 that the reaction of aryl diazonium salts with mercury electrodes results in electrografting of aryl groups on this liquid metal with formation of phenylmercuric chloride and diphe-nylmercury (Elofson, R.M., Can. J. Chem., 1958, 36, 1207–1210, doi: 10.1139/v58-174; see also Chapter 1). Later in 1961, aryl diazonium salts were proposed as coupling agents in histochemistry for the labeling of enzymes (Burstone, M.S., Weisburger, E.K., J. Histochem. Cytochem., 1961, 9, 301–303, doi: 10.1177/9.3.301).

In modern surface science, Jean Pinson and co-workers described, in 1992, the mechanisms of the reaction between aryl diazonium salts and glassy carbon elec-trodes resulting in surface-tethered aryl groups. Provided that the functional group, in para position of the diazonium, is reactive, it becomes possible to graft polymers, enzymes, catalysts, etc. Since then, the two last decades (1992–2012) witnessed a quantum jump in the number of publications pertaining to surface chemistry and applications of aryl diazonium salts. The interest in using these compounds obviously lies in their ease of preparation, rapid reduction by a large range of methods and strong aryl-surface covalent bonding. Grafted aryl groups can be used as such in order to impart new physicochemical properties, or can serve as coupling agents for additional species. The applications concern electron-ics, electrocatalysis, sensors, nanocomposites, drug delivery, to name but a few, as testified by over 3000 articles and reviews, book chapters, and chapter sections. Several processes involving aryl diazonium salts were also patented and industrial products, though not too many, are on the market (see Chapter 14). Despite these extraordinary academic and industrial achievements, there is no comprehensive book dealing with the fundamental aspects of surface and interface chemistry of the diazonium salts and their use as surface modifiers and coupling agents. The

XVI Preface

book that you are holding in your hands fills this gap in 14 self-contained chapters written by acknowledged experts in their respective fields.

One can distinguish three main parts: fundamental and analytical aspects of diazonium-modified surfaces (Chapters 1–4); applications of diazonium salts in electrocatalysis, polymer science, sensors and biosensors, and electronics (Chap-ters 5–11). The third part concerns related or alternative organic molecules (e.g. amines, triazenes, vinyl, ethynyl, Grignard reagents) for surface treatment in general (Chapter 12) and for the more applied molecule-silicon electronics, in particular (Chapter 13). The book finishes by a contribution summarizing patents and industrial applications of the surface chemistry of aryl diazonium salts and related compounds (Chapter 14).

Dear Reader, we would like to thank you for choosing our book. As you will appreciate, the surface chemistry of diazonium salts and related compounds has progressed at a remarkable pace. The gap between the academic research on dia-zonium salt surface chemistry and its industrial applications has already been filled although this topic of surface science and technology is still in its infancy. Whether you are a student, technician, engineer, teacher or researcher; expert or newcomer, it is hoped that the information provided by all contributors will open new horizons.

As an editor, it has been a very exciting experience to collaborate with acknowl-edged experts from the five continents. I should like to thank them all for kindly accepting my invitations to contribute to this adventure. I am also very much indebted to all reviewers for their guidance. I am grateful to my colleague, Dr. Abderrahim Boudenne (Université Paris Est Créteil, France), for his remarkable help when I started the book project. I must also add here that I, personally, as well as my students, have learned a lot from Professor Jean Pinson. I have enjoyed his teaching of chemical kinetics and magneto-chemistry when I was one of his third year students in 1981 at University Paris 7; it is both and an honor and a privilege to have him as a colleague 30 years later. It therefore gives me great pleasure to dedicate this book to my former professor of chemistry and actual colleague and friend Jean Pinson.

This experience has been intense and exciting over almost 2 years. It would not have been possible to put the book in its final form, in such a short period of time, without the continuous support, encouragement, love, and patience of my daugh-ter Inès, my son Selim, and my wife Heger.

March 2012 Mohamed Mehdi Chehimi

XVII

ListofContributors

Dinesh K. AswalBhabha Atomic Research CentreTechnical Physics DivisionTrombayMumbai 400 085India

James A. BelmontCabot Corporation Business and Technology Center157 Concord RoadP.O. Box 7001BillericaMA 01821USA

Adam Johan BergrenUniversity of AlbertaNational Institute for Nanotechnology11421 Saskatchewan DriveEdmontonAB T6G 2M9Canada

Christophe BureauAdvanced Material Technology Consulting9 Avenue Paul Verlaine38030 Grenoble Cedex 2France

Mohamed M. ChehimiUniversity Paris DiderotSorbonne Paris CitéITODYSUMR CNRS 708615 rue J-A de Baïf75013 ParisFrance

Sheng DaiOak Ridge National LaboratoryChemical Sciences DivisionP.O. Box 2008, MS 6201Oak RidgeTN 37831-6201USAandUniversity of TennesseeDepartment of ChemistryKnoxvilleTN 37966USA

Guy DeniauCEA-SaclayIRAMISSPCSI Chemistry of Surfaces and Interfaces Group91191 Gif-sur-YvetteFrance

XVIII ListofContributors

Alison J. DownardUniversity of CanterburyDepartment of ChemistryMacDiarmid Institute for Advanced Materials and NanotechnologyPrivate Bag 4800Christchurch 8140New Zealand

Sarra Gam-DerouichUniversity Paris DiderotSorbonne Paris CitéITODYSUMR CNRS 708615 rue J-A de Baïf75013 ParisFrance

Jalal GhilaneUniversity Paris DiderotSorbonne Paris CitéITODYSUMR CNRS 708615 rue J-A de Baïf75013 ParisFrance

J. Justin GoodingUniversity of New South WalesSchool of Chemistry and Australian Centre for NanoMedicineSydney 2052Australia

Andrew J. GrossUniversity of CanterburyDepartment of ChemistryMacDiarmid Institute for Advanced Materials and NanotechnologyPrivate Bag 4800Christchurch 8140New Zealand

Alicia L. GuiUniversity of New South WalesSchool of ChemistrySydney 2052Australia

Dao-Jun GuoQufu Normal UniversitySchool of Chemistry and Chemical EngineeringThe Key Laboratory of Life-Organic AnalysisQufuShandong 273165China

Shiv Kumar GuptaBhabha Atomic Research CentreTechnical Physics DivisionTrombayMumbai 400 085India

Karsten HinrichsLeibniz-Institut für Analytische Wissenschaften – ISAS- e.V.Department BerlinAlbert-Einstein-Straße 912489 BerlinGermany

De-en JiangOak Ridge National LaboratoryChemical Sciences DivisionP.O. Box 2008, MS 6201Oak RidgeTN 37831-6201USA

ListofContributors XIX

Shankar Prasad KoiryBhabha Atomic Research CentreTechnical Physics DivisionTrombayMumbai 400 085India

Jean Christophe LacroixUniversity Paris DiderotSorbonne Paris CitéITODYSUMR CNRS 708615 rue J-A de Baïf75013 ParisFrance

Guozhen LiuCentral China Normal UniversityKey Laboratory of Pesticide and Chemical Biology of Ministry of EducationCollege of Chemistry152# Luoyu RoadWuhan 430079China

Samia Mahouche-CherguiUniversity Paris DiderotSorbonne Paris CitéITODYSUMR CNRS 708615 rue J-A de Baïf75013 ParisFrance

Pascal MartinUniversity Paris DiderotSorbonne Paris CitéITODYSUMR CNRS 708615 rue J-A de Baïf75013 ParisFrance

Richard McCreeryUniversity of AlbertaNational Institute for Nanotechnology11421 Saskatchewan DriveEdmontonAB T6G 2M9Canada

Alice MesnageCEA-SaclayIRAMISSPCSI Chemistry of Surfaces and Interfaces Group91191 Gif-sur-YvetteFrance

Fakhradin MirkhalafCoventry UniversitySonochemistry CentreCoventry, CV1 5FBUKNanomedpharma (NMP) LtdEden BuildingLiverpool Hope UniversityHope ParkLiverpool, L16 9JDUK

Serge PalacinCEA-SaclayIRAMISSPCSI Chemistry of Surfaces and Interfaces Group91191 Gif-sur-YvetteFrance

XX ListofContributors

Jean PinsonESPCI, Laboratoire Sciences Analytiques, Bioanalytiques et Miniaturisation10 rue Vauquelin75231 Paris Cedex 05FranceandUniversity Paris DiderotSorbonne Paris CitéITODYSUMR CNRS 708615 rue J-A de Baïf75013 ParisFrance

Fetah I. PodvoricaUniversity of PrishtinaFaculty of Mathematical and Natural SciencesChemistry Departmentrr. “Nena Tereze” nr. 510 000 PrishtinaKosovo

Hyacinthe RandriamahazakaUniversity Paris DiderotSorbonne Paris CitéITODYSUMR CNRS 708615 rue J-A de Baïf75013 ParisFrance

Jörg RappichHelmholtz-Zentrum Berlin für Materialien und Energie GmbHInstitut für Silizium-PhotovoltaikKekuléstraße 512489 BerlinGermany

Hatem Ben RomdhaneCampus UniversitaireFaculté des Sciences de TunisLaboratoire de Chimie Organique Structurale et Macromoléculaire2092 El Manar IITunisia

Katy RoodenkoThe University of Texas at DallasDepartment of Materials Science & EngineeringMail Station RL10800 W. Campbell RoadRichardsonTX 75080-3021USA

Luis SantosUniversity Paris DiderotSorbonne Paris CitéITODYSUMR CNRS 708615 rue J-A de Baïf75013 ParisFrance

Nan ShaoOak Ridge National LaboratoryChemical Sciences DivisionP.O. Box 2008, MS 6201Oak RidgeTN 37831-6201USA

ListofContributors XXI

Bradley M. SimonsUniversity of CanterburyDepartment of ChemistryMacDiarmid Institute for Advanced Materials and NanotechnologyPrivate Bag 4800Christchurch 8140New Zealand

Lorraine TessierCEA-SaclayIRAMISSPCSI Chemistry of Surfaces and Interfaces Group91191 Gif-sur-YvetteFrance

Gaelle Trippe-AllardUniversity Paris DiderotSorbonne Paris CitéITODYSUMR CNRS 708615 rue J-A de Baïf75013 ParisFrance

Xin ZhangHelmholtz-Zentrum Berlin für Materialien und Energie GmbHInstitut für Silizium-PhotovoltaikKekuléstraße 512489 BerlinGermany

1

1

Aryl Diazonium Salts: New Coupling Agents in Polymer and Surface Science, First Edition. Edited by Mohamed Mehdi Chehimi.© 2012 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2012 by Wiley-VCH Verlag GmbH & Co. KGaA.

AttachmentofOrganicLayerstoMaterialsSurfacesbyReductionofDiazoniumSaltsJeanPinson

1.1ABriefSurveyoftheChemistryandElectrochemistryofDiazoniumSalts

Aromatic diazonium salts (ArN2+ X−) are easily synthesized in an acidic aqueous

medium (HBF4) starting from an amine in the presence of NaNO2, and in an aprotic medium (ACN + HBF4 in ether) in the presence of t-butylnitrite or in ACN + NOBF4 [1–2]. As many aromatic amines are available commercially, the preparation of a large number of diazonium salts can be easily carried out. They can be isolated and characterized, but they can be used directly in the solution where they have been prepared [3].

The chemistry of aromatic diazonium salts [1, 4, 5] is dominated by the elec-trophilic character of the azo group; they react with aromatic amines and phenols to give azo dyes (C-coupling) that are important coloring materials [6]. Aliphatic diazonium salts are extremely unstable and up to now only a few examples of grafting on carbon black involving the diazonium salt of 2-aminoethanesulfonic acid and 4-bromobenzylamine have been reported [1, 7].

As we will see below, when a diazonium reacts with a surface, with a few reported exceptions, the diazonium group is lost and the radical reacts with the surface, therefore grafting involves a homolytic dediazonation step; in this respect the dediazonation reactions are important for discussing the grafting mechanism. This dediazonation can take place heterolytically to give Ar+ cations, or homolyti-cally to give Ar. radicals [8]; these spontaneous reactions can be slowed down by reducing the temperature to below 5 °C. The Sandmeyer reaction (1.1) is a first example of an important dediazonation reaction involving a radical; the reduction of the diazonium salt by cupric chloride or bromide ArCl, (Br) gives an aryl radical that abstracts a chlorine (bromine) atom from CuCl (Br) to give ArCl (Br), as shown in the reaction.

2 1 AttachmentofOrganicLayerstoMaterialsSurfacesbyReductionofDiazoniumSalts

ArN Cl CuCl ArCl N2 2+ − + → + (1.1)

A second important dediazonation reaction of diazonium salts in relation to graft-ing is the Gomberg–Bachman reaction; in the presence of a base the diazonium group is lost to give radicals that couple to other aromatic groups, dimers and a number of other coupling products are obtained [9, 10]. The Pschorr reaction is the intramolecular reaction of an aryl radical with an aryl group, the radical is produced, for example, by reduction of a diazonium salt by Cu(0) [11]. Merweein reactions also rely on the formation of radicals [12]. Solvolytic dediazonations are another example, they can take place in a heterolytic or homolytic manner, that is, through the intermediacy of an aryl cation or an aryl radical [13–17]; heterolytic dediazonation takes place in solvents of low nucleophilicity (H2O), while a homo-lytic mechanism is observed in solvents of increased nucleophilicity (HMPT, pyridine), in a number of solvents, such as MeOH, EtOH, DMSO, both mecha-nisms can be observed [14]. For example, in ethanol a slow heterolytic mechanism is observed in an acid medium and a 50 times faster homolytic one in a basic medium [14]. For a given solvent, electron-withdrawing substituents in the aro-matic ring favor homolytic dediazoniations [14].

In an aqueous acidic medium and in aprotic non-nucleophilic solvents diazo-nium salts are present, but at neutral and basic pHs [13–17] equilibria between the diazohydroxide and diazoates are established; they are displaced toward the formation of diazoates; equilibrium and rate constants have been measured [13]. In the presence of alcohols, diazoethers Ar–N=N–OEt [13, 18] , and in the presence of amines, triazenes Ar–N=N-(NR2) are obtained. These derivatives can also be used for surface modification. For example, diazohydroxides can spontaneously dediazonize and the ensuing radical attaches to the surface of gold [19]. Triazenes are interesting because they are transformed into diazonium salts in an acid medium; in 2% HF the oxidized silicon surface is transformed into Si–H and aryldiethyltriazenes are transformed into aryldiazonium salts, followed by sponta-neous grafting of the aryl species to the silicon surface [20]. They can also generate aryldiazonium salts in the presence of electrogenerated acid produced by oxidation of hydrazine [21].

Prior to the discovery of the electrografting reaction, the reduction of diazonium salts ArN2

+ X− had been investigated in an aqueous medium at mercury electrodes [22]. In an aqueous acidic medium two waves are observed; the first is a one-electron wave, while the overall process involves four electrons on the second wave and leads to phenylhydrazine. The formation of the aryl radical was confirmed by coulometry, on a mercury pool, at the potential of the first wave, that provided, nearly exclusively, phenylmercuric chloride and diphenylmercury by reaction of phenyl radicals with mercury. Note that these mercury compounds can be viewed as the result of electrografting on a liquid metal. The involvement of radicals [23] during the electrochemical reduction (on the first wave) of aryldiazo-nium salts was also observed through the Pschorr synthesis of phenanthrene [24], and also by electron spin resonance (ESR) in ACN in the presence of a spin-trap [25].

1.2 TheDifferentMethodsthatPermitGraftingofDiazoniumSalts 3

1.2TheDifferentMethodsthatPermitGraftingofDiazoniumSalts

In this section we describe the many methods that permit the grafting of diazo-nium salts, on many substrates, through a variety of experimental conditions.

1.2.1Electrochemistry

This is the first method that was used for grafting (electrografting) diazonium salts [26–29]. Electrochemistry of diazonium salts in an aprotic medium is very simple, a single, broad, one-electron wave is observed at potentials close to 0 V vs SCE as presented in Table 1.1.

The attachment of the ensuing aryl radical (1.2) + (1.3) (Figure 1.1) to the carbon or metal substrate translates in the fast disappearance of the wave due to the block-ing of the electrode by the organic layer formed on it. This is, most likely, the reason for the broadness of the wave; the surface is modified while the vol-tammogram is recorded. Sometimes a prepeak is observed; on gold, it has been

Table1.1 Some reduction potentials on GC of benzenediazonium salts in ACN.

Diazoniumsalt Reductionpotential,VvsSCE

4-Nitrobenzenediazonium +0.20 [27]4-Bromobenzenediazonium +0.02 [27]Benzenediazonium −0.06 [27]4-t-Butylbenzenediazonium −0.10 [30]4-Methylbenzenediazonium −0.16 [30]4-Diethylaminobenzenediazonium −0.56 [31]

Figure1.1 (a) Cyclic voltammogram and (b) chronoamperometry of 4-nitrobenzenediazonium (c = 5 mM) in ACN + 0.1 M NBuBF4: 1, first and 2, second scan. Gold electrode (d = 1 mm), v = 100 mV s−1, reference Ag/AgCl.

1

(a) (b)

0

1

I/µA

E/mV/(Ag/AgCl)

2−1

−2

−3

−4−900 −700 −500 −300 −100 100

5

−5

I/µA

t/s

−15

−25

−35

−45−2 4 10 16 22 28

4 1 AttachmentofOrganicLayerstoMaterialsSurfacesbyReductionofDiazoniumSalts

assigned to the reduction on the different crystallographic facets of gold, for example, the diazonium salt +N2–C6H4–S–C6F13 presents three voltammetric peaks on polycrystalline gold at +0.14, +0.03 and ∼−0.45 V vs (Ag/Ag+), that are assigned respectively to Au (111), Au (100) and Au (110) + Au (331) [32].

ArN e Ar N2 21+ −+ → +i (1.2)

Surf Surf+ →Ar -Ari (1.3)

Ar e Ari + →− −1 (1.4)

The Ar. radical is responsible for the grafting reaction, its formation and its further evolution are, therefore, important in the context of surface modification. It has been shown, by simulation of the voltammograms, that the reduction of the ben-zenediazonium cation (1.2) is a concerted reaction, which means that, during the electrochemical reduction at the peak potential, there are no intermediates between the diazonium cation and the radical; this also means that the radical is formed directly on the surface, which is a very favorable situation for the grafting reaction [33]. This radical can be reduced, in turn, to an anion (1.4) that is unfavorable for the grafting reaction. The reduction potential of Ar. has been measured not only by simulation of the voltammetric curves: E = −0.64 V vs SCE [33], but also from the number of electrons consumed at different potentials for the reduction of benzenediazonium, diphenyliodonium and triphenylsulfonium salts, which all provide a phenyl radical upon reduction: E = −0.95 V vs SCE [34]. The standard redox potential has been measured by simulation of the voltammograms [33]: E°(Ph./Ph−) = +0.05 V vs SCE; it has also been calculated by DFT methods: E°(Ph./Ph−) = −0.26 V vs SCE [35]. These indicate that the reduction of Ar. is quite easy, which means that during electrografting the potential should not be too negative in order to prevent the reduction of the radical. This is shown by the reduction of different diazonium salts at −1.0 V vs SCE (at a potential where the radical is reduced to an anion), on a mercury electrode, in acetonitrile; azobenzenes were obtained in good yields but no mercury compounds were reported [36].

The formation of the layer can be easily detected, as shown in Figure 1.1, through the disappearance of the reduction wave of the diazonium salt; chronoam-perometry is also very characteristic, instead of a decrease in the current according to a Cotrell law, a very sharp decrease is observed due to the fast blocking of the surface.

1.2.2ReducingSubstrate,HomolyticDediazonation,ReactionwiththeSubstrate

Table 1.1 exemplifies the easy reduction of diazonium salts; if the substrate has reducing capabilities an aryl radical will be formed, close to the electrode, by simply dipping the substrate in the solution of the diazonium salt. In some other examples, where the substrate is less reducing, it is difficult to differentiate a reduction by the substrate from a spontaneous dediazonation. Indeed, a spontane-ous homolytic dediazonation is another route for the formation (in solution) of

1.2 TheDifferentMethodsthatPermitGraftingofDiazoniumSalts 5

aryl radicals. But the substrate can also react chemically with the diazoniums salt or the aryl cation Ar+ (and not the radical) and two examples are described in the section on the grafting mechanism.

Metals such as iron and copper can reduce diazonium salts and 4-nitrophenyl layers are obtained by dipping copper, iron, nickel and zinc in a solution of the corresponding salt [37]. The grafting process is in agreement with a redox reaction: grafting is more efficient on zinc than on iron, and even more than on nickel; this trend follows the open-circuit potential order EOCP(Zn) < EOCP(Fe) < EOCP(Ni) and, on a selected metal, grafting is more difficult with less-easily reduced diazonium salts. Benzenediazonium tetrafluoroborate has been reacted in ACN with various metals (Al, Ca, Cr, Cu, Fe, Ga, In, Mg, Li, Na, or Zn), nitrogen evolution was observed, indicating the reduction of the diazonium salt. With copper a ionization-dissolution was evidenced at high concentration and the formation of a complex [Cu(N2C6H5) (NC–CH3)3]+ was demonstrated [38]. On gold a spontaneous grafting occurs in acidic [19, 39, 40] solution but the mechanism is unclear. These results indicate that the redox properties of both partners (diazonium + metal) are involved in the grafting reaction.

On glassy carbon, the mechanism seems to follow a reductive path as the easily reducible 4-nitro, 4-trifluoromethyl, or 4-bromobenzenediazonium (Ep = +0.20, −0.34, −0.35 V vs SCE, respectively) are grafted spontaneously, but not the diazo-nium salts of diethyl, amino diphenyl, triphenyl aniline (Ep = −0.42, −0.35 and −0.45 V, respectively) [41] nor N,N-diethylaminobenzenediazonium (Ep = −056 V vs SCE) [31]. Moreover, a jump in the open circuit potential of the carbon electrode was observed upon addition of the 4-nitrobenzenediazonium salt in solution [41, 42]. These features point to an electron transfer mechanism and to the interme-diacy of the aryl radical. Spontaneous grafting of diamond has also been observed [43, 44]; the reaction time necessary to obtain a monolayer (72 h in an ACN satu-rated solution of 4-nitrobenzenediazonium) [43] is more in agreement with a homolytic spontaneous dediazonation than with an electron transfer from the surface. Carbon nanotubes (CNTs) can also be modified spontaneously [45]. In pure water (where diazoates should be present), the mechanism has been assigned (through a careful kinetic analysis and ESR measurements) to a spontaneous homolytic dediazonation [46].

Spontaneous grafting can also be achieved on hydrogenated silicon, the sub-strate reduces the diazonium salt to a radical [47], this is described in more detail below. At a scanning electrochemical microscope SECM tip the pH can be modi-fied and fluoride ions transformed into HF that etches the native oxide of a Si wafer, 4-nitrobenzenediazonium can be grafted spontaneously in the holes [48].

1.2.3ReducingReagent

As diazonium salts are very easily reduced, a number of reducing reagents can be used. Hypophosphorous acid (H3PO2) has been used to functionalize the surface of carbon powder [49–54], polymers (polypropylene, polyethylterephthalate,

6 1 AttachmentofOrganicLayerstoMaterialsSurfacesbyReductionofDiazoniumSalts

polyethyletherketone) and inorganic compounds (TiN, SiC, SiO2, SiOC) [55]. Iron powder has also been used as a reducing agent for the grafting of diazoniums alone or diazonium and vinylics [56]; in this last case, the process is very efficient as even the surface of glass or Teflon can be modified. Gold surfaces have been modified in the presence of ascorbic acid [40]. With these methods, the radical is produced in solution and there should be no limitation to the growth of the layers, but no data about the thicknesses are given.

1.2.4NeutralandBasicMedia

In a neutral aqueous medium diazohydroxides are obtained, they rapidly deproto-nate to diazoates that decompose radicals [13]; these radicals react spontaneously with metals [57] and graphene sheets [58]. In basic and neutral media, diazoniums are transformed directly into diazoates; gold surfaces have been modified in this way [19, 40]. Iron oxide magnetite, Fe3O4, nanoparticles have been capped by aryl groups, by adding the 2-hydroxyethylbenzenediazonium tetrafluoroborate (BF4, N2–C6H4–(CH2)2–OH) directly in the pH 9 solution where the nanoparticles are formed [59]. Carbon nanotubes have been modified spontaneously in a diazoate solution at pH 11 [60]. In these cases, a homolytic dediazonation is known to take place [13, 14].

1.2.5Ultrasonication

Grafting of various inorganics and polymers (see above) has been achieved under ultrasonication [55]. Diamond nanoparticles have also been modified under ultra-sonication by 4-nitrophenyl groups in acidic aqueous solution [44]. ITO has been modified by 4-nitrobenzenediazonium, in water, at different frequencies, the lowest one (20 kHz) was shown to be the most efficient [61]. A mechanism has been proposed, based on the known formation of reducing radicals (H., R. from adventitious impurities), these radicals should reduce the diazonium salt [61].

1.2.6HeatingandMicrowave

The surface of polyethylterephtalate has been modified by heating an aqueous solution of sulfanilic acid at 70 °C in the presence of NaNO2 [62]; under these conditions a heterolytic cleavage of the diazonium cation should be favored. Thermal reactions, using in situ generated aryl diazonium salts, have permitted the derivatization of SWCNTs (single wall carbon nanotubes) at 60 °C in dichlo-robenzene for 15 h [45], and MWCNTs (multiwall carbon nanotubes) at 80 °C in concentrated sulfuric acid in the presence of ammonium persulfate and 2,2-azoisobutyronitrile [63]. A microwave-assisted surface modification of CNTs and nanohorns has been described [64–66]. Heating aryldiazonium tetrafluorobo-