Conjugated Polyelectrolytes: Fundamentals and Applications

T his is the first monograph to specifically focus on fundamentals and applications of polyelectrolytes, a class of molecules that gained substantial interest due to their unique combination of properties. Combining both features of organic semiconductors and polyelectrolytes, they offer a broad field for fundamental research as well as applications to analytical chemistry, optical imaging, and opto–electronic devices. The initial chapters introduce readers to the synthesis, optical and electrical properties of various conjugated polyelectrolytes. This is followed by chapters on the applications of these materials in optical sensing and imaging with emphasis on biological systems, while the final section addresses the emerging applications of conjugated polyelectrolytes in optoelectronic devices, concluding with an in–depth discussion of structure–property relationship. The editors and contributors are all pioneers and experts in this expanding field. This monograph is not only for chemists, materials scientists, and physicists, but also a unique source of knowledge for readers with scientific background interested in polyelectrolytes.

Preface XIII List of Contributors XV 1 Design and Synthesis of Conjugated Polyelectrolytes 1 Kan–Yi Pu, Guan Wang, and Bin Liu 1.1 Introduction 1 1.2 Poly(arylene)s 2 1.2.1 Polythiophenes 2 1.2.1.1 Anionic Polythiophenes 2 1.2.1.2 Cationic Polythiophenes 6 1.2.1.3 Zwitterionic Polythiophenes 6 1.2.2 Poly(p–phenylene)s 6 1.2.2.1 Anionic Poly(p–phenylene)s 6 1.2.2.2 Cationic Poly(p–phenylene)s 10 1.2.3 Poly(fluorene)s 12 1.2.3.1 Cationic Poly(fluorene)s 12 1.2.3.2 Anionic Poly(fluorene)s 22 1.2.3.3 Zwitterionic Poly(fluorene)s 31 1.3 Poly(arylene ethynylene)s 31 1.3.1 Poly(phenylene ethynylene)s 31 1.3.1.1 Anionic Poly(phenylene ethynylene)s 31 1.3.1.2 Cationic Poly(phenylene ethynylene)s 37 1.3.2 Poly(fluorene ethynylene)s 42 1.3.2.1 Cationic Poly(fluorene ethynylene)s 42 1.3.2.2 Anionic Poly(fluorene ethynylene)s 45 1.4 Poly(arylene vinylene)s 48 1.4.1 Poly(phenylene vinylene)s 48 1.4.1.1 Anionic Poly(phenylene vinylene)s 48 1.4.1.2 Cationic Poly(phenylene vinylene)s 50 1.4.2 Poly(fluorene vinylene)s 53 1.4.2.1 Cationic Poly(fluorene vinylene)s 53 1.4.2.2 Anionic Poly(fluorene vinylene)s 58 1.5 Conclusion 59 References 60 2 All–Conjugated Rod–Rod Diblock Copolymers Containing Conjugated Polyelectrolyte Blocks 65 Ullrich Scherf, Rachel C. Evans, Andrea Gutacker, and Guillermo C. Bazan 2.1 Introduction 65 2.2 All–Conjugated, Cationic Polyfluorene–b–Polythiophene Diblock Copolymers 67 2.2.1 Synthesis 67 2.2.2 Optical Properties 70 2.2.3 Aggregation Behavior of Cationic PF–b–PT Diblock Copolymers 73 2.2.4 Atomic Force Microscopy 73 2.2.4.1 Confocal Microscopy 75 2.2.4.2 Complexation with Anionic Surfactants 75 2.2.4.3 Complexation with DNA 77 2.2.4.4 Incorporation of PF2/6–b–P3TMAHT into Organic Electronic Devices 79 2.3 All–Conjugated Cationic Polyfluorene–b–Polyfluorene Diblock Copolymers 81 2.3.1 Synthesis 81 2.3.2 Optical Properties 82 2.3.3 Atomic Force Microscopy 83 2.4 Conclusion 85 Acknowledgments 86 References 87 3 Ionically Functionalized Polyacetylenes 91 Stephen G. Robinson and Mark C. Lonergan 3.1 Introduction 91 3.2 Polymers from Ionically Functionalized Cyclooctatetraenes 92 3.2.1 Synthesis and General Properties 92 3.2.2 Electrochemistry 96 3.2.2.1 Electrochemical Doping 96 3.2.2.2 The Donnan Potential 101 3.2.2.3 Internal Compensation 102 3.2.3 Polyelectrolyte–Mediated and Self–Limiting Electrochemistry 103 3.2.4 Junctions 104 3.2.4.1 In situ Electrochemical Manipulation and the Tunable Diode 105 3.2.4.2 Internally Compensated p–n Junctions 106 3.2.4.3 Undoped Ionic Junctions 109 3.3 Polymers from Ionically Functionalized Acetylenes 112 3.3.1 General Properties and Synthetic Approaches 112 3.3.2 Polymer Chain Structure 113 3.3.3 Poly(IA)s with Extended Conjugations 116 3.4 Summary 122 Acknowledgment 122 References 122 4 Aggregation Properties of Conjugated Polyelectrolytes 127 Hugh D. Burrows, Matti Knaapila, Sofia M. Fonseca, and Telma Costa 4.1 Introduction 127 4.2 Aggregation: from Disordered Clusters to Structured Vesicles 128 4.3 Experimental Studies on Aggregation 132 4.3.1 What Scattering Techniques Tell Us 132 4.3.2 Microscopy Studies in Solution and Films 135 4.3.3 Spectroscopic and Photophysical Studies 137 4.3.4 Aggregation as Seen by Electrical Conductivity and NMR Spectroscopy 141 4.3.5 Molecular Dynamics Simulations 144 4.4 Conjugated Polyelectrolyte Aggregation in Solution 146 4.4.1 Effect of Structure and Charge: Intramolecular and Intermolecular Effects 146 4.4.2 Effect of Solvent and Cosolvent 146 4.4.3 Decreasing Aggregation through Side–Chain and Charge Density Modification 150 4.4.4 Aggregation in Ionic Conjugated Block Copolymers 151 4.5 Learning How to Control Aggregation 153 4.5.1 Interactions with Surfactants 153 4.5.2 Conjugated Polyelectrolyte/Polyelectrolyte and Polyelectrolyte/Water–Soluble Polymer Systems 156 4.5.3 Metal–Ion–Induced Aggregation 159 4.5.4 Aggregation and Nanostructuring 161 4.6 Conclusions and Outlook 162 References 164 5 Sensing via Quenching of Conjugated Polyelectrolyte Fluorescence 169 Danlu Wu, Jie Yang, Fude Feng, and Kirk S. Schanze 5.1 Background and Introduction 169 5.2 Small Ions/Molecules Sensing 173 5.2.1 Introduction 173 5.2.2 Small–Ion Sensing 174 5.2.2.1 Positively Charged Ion Sensing 174 5.2.2.2 Negatively Charged Ion Sensing 175 5.2.3 Factors that Influence Amplified Quenching 176 5.2.3.1 Conjugated Polyelectrolyte Aggregation 176 5.2.3.2 Conjugated Polyelectrolyte Chain Length 177 5.2.3.3 Quencher Properties and Binding Mode 177 5.2.4 Small Biomolecules Sensing 179 5.2.4.1 Pyrophosphate Sensing 179 5.2.4.2 Glucose Sensing 180 5.2.5 Summary 181 5.3 Protein and Enzyme Activity Sensing 181 5.3.1 Protein Sensing 181 5.3.1.1 Introduction 181 5.3.1.2 Quencher–Tether–Ligand Approach 182 5.3.1.3 Direct Quenching Approach 184 5.3.1.4 CPE–Coated Fibers 185 5.3.2 Enzyme Activity Sensing 185 5.3.2.1 Introduction 185 5.3.2.2 Fluorescence Turn–On and Turn–Off Assays 186 5.3.3 Summary 191 5.4 DNA sensing 192 5.4.1 Introduction 192 5.4.2 DNA Sensing Methods 193 5.4.2.1 Electrostatic Complex–Based DNA Sensing 193 5.4.2.2 Covalently Linked DNA–CPE Hybrids: Molecular Beacons 194 5.4.2.3 CPE–Based Heterogeneous Sensor Platforms for DNA 195 5.5 Concluding Remarks 196 References 197 6 Sensing Applications via Energy Transfer from Conjugated Polyelectrolytes 201 Fengting Lv, Shu Wang, and Guillermo C. Bazan 6.1 Introduction 201 6.2 DNA and RNA Sensing with Conjugated Polyelectrolytes 206 6.2.1 DNA Sequence 206 6.2.2 DNA Conformation Sensing 210 6.2.3 DNA SNP Detection 211 6.2.4 DNA Methylation 213 6.2.5 RNA Sensing 213 6.3 Protein Sensing with Conjugated Polyelectrolytes 215 6.3.1 Protein Sensing 215 6.3.2 Enzyme Sensing 217 6.3.3 Drug Screening with CPEs 220 6.4 Biological/Chemical Small–Molecules Sensing with Conjugated Polyelectrolytes 222 6.4.1 Metal Ion Sensing 222 6.4.2 Glucose Sensing 222 6.4.3 Cysteine Detection 222 6.4.4 Antioxidant Detection 224 6.4.5 Differential Response Arrays 224 6.5 Conclusion 227 References 227 7 Sensing via Conformational Changes of Conjugated Polythiophenes 231 Even J. Lemieux and Mario Leclerc 7.1 Introduction 231 7.2 Structural Characteristics of Conjugated Polythiophenes 232 7.3 Thermochromic Sensors 233 7.4 Ionochromic Sensors 233 7.4.1 Detection of Cations 233 7.4.2 Detection of Anions 234 7.5 Affinitychromic Sensors 235 7.5.1 Detection of Chemical Compounds 236 7.5.2 Detection of Low–Molecular–Weight Biological Molecules 239 7.5.3 Detection of High–Molecular–Weight Biological Molecules 242 7.5.3.1 Detection of DNA and RNA 242 7.5.3.2 Detection of Proteins 251 7.6 Conclusions 256 References 256 8 Conjugated Polyelectrolyte–Based Biocide Applications 263 Thomas S. Corbitt, Eunkyung Ji, Ying Wang, Anand Parthasarathy, Kristin N. Wilde, Eric H. Hill, Dimitri Dascier, Heather E. Canavan, Eva Y. Chi, Kirk S. Schanze, and David G. Whitten 8.1 Introduction 263 8.2 Dark Bactericidal Activity of Conjugated Polyelectrolytes 266 8.2.1 Action Models of AMPs and Synthetic Cationic Polymers 266 8.2.2 The Lethal Effect of CPEs in the Dark 267 8.2.2.1 The Role of Cell Wall and Cytoplasm Membrane 268 8.2.2.2 The Relationship of CPE Structure to Membrane Selectivity 270 8.3 Light–Activated Biocidal Activity 271 8.3.1 Mechanism 271 8.3.2 Other Interactions 273 8.4 Photochemistry, Photophysics, and Modeling 274 8.4.1 Photochemistry and Photophysical Properties of CPEs 274 8.4.2 Modeling of PPEs 274 8.4.3 Photodegradation 276 8.5 Conjugated Cationic Oligomers and Polymers as Antimicrobials 278 8.5.1 Effect of Molecular Weight on Antimicrobial Activity 278 8.5.2 Effect of Structure on Antimicrobial Activity 279 8.5.3 Thiophene–Based Oligomers 280 8.6 Incorporation into Other Materials and Formats 281 8.6.1 Fabrics 283 8.6.2 Multilayers 284 8.7 Activity against Viruses and Biofilms 284 8.7.1 Antiviral Activity of CPEs 284 8.7.2 Biofilms Biocidal Activity of ‘‘End Only’’ Oligo(phenylene ethynylene)s (EO–OPEs) 287 8.8 Toxicity toward Mammalian Cells 288 8.8.1 Cell Monolayers 289 8.8.2 Tissues 289 8.9 Summary and Outlook 291 References 292 9 Conjugated Polyelectrolyte–Based Imaging and Monitoring of Protein Aggregation 295 K. Peter R. Nilsson and Per Hammarstr¨om 9.1 Introduction 295 9.2 CPEs for Bioimaging 296 9.3 Amyloid Fibrils and Protein Aggregation Diseases 299 9.3.1 CPEs for the Detection of Amyloid Fibrils in Solution 302 9.3.2 CPEs for Histological Staining of Amyloid Deposits in Tissue Sections 303 9.4 Novel Scaffolds for the Detection of a Diversity of Protein Aggregates 307 9.4.1 LCOs for In Vivo Imaging of Amyloid Deposits 310 9.5 Conclusion 312 References 312 10 Charge Injection Mechanism in PLEDs and Charge Transport in Conjugated Polyelectrolytes 315 Peter Zalar and Thuc–Quyen Nguyen 10.1 Introduction 315 10.2 Charge Injection Mechanism in Polymer Light–Emitting Diodes Using Conjugated Polyelectrolytes as Electron–Injecting/Transporting Layers 315 10.2.1 Charge Injection in Organic Semiconducting Devices 315 10.2.2 Charge Injection Mechanism in Multilayer PLEDs Using Thick CPE Electron–Injecting/Transporting Layers 317 10.2.3 Charge Injection Mechanism in Multilayer PLEDs Using Thin CPE Electron–Injecting/Transporting Layers 322 10.2.4 Improving the Turn–on Time of Multilayer PLEDs Using CPE Electron–Injecting/Transporting Layers 325 10.3 Charge Transport in Conjugated Polyelectrolytes 329 10.3.1 Charge Transport in Conjugated Polymers 329 10.3.2 Measuring Charge Transport 332 10.3.3 Measuring Electron Transport in Conjugated Polyelectrolytes 333 10.3.4 Influence of Chemical Structure on Electron Transport 334 10.3.4.1 Effect of Counterion on Electron Transport of Cationic CPEs 334 10.3.4.2 Effect of Conjugated Backbone and Charge Reversal on the Electron Transport of CPEs 336 10.3.4.3 Temperature–Dependent Electron Transport of CPEs 336 10.3.5 Hole Transport in Thiophene and Thieno[3,2–b]thiophene–Based Conjugated Polyelectrolytes 340 10.4 Conclusion 341 References 342 11 Organic Optoelectronic Devices Containing Water/Alcohol–Soluble Conjugated Polymers and Conjugated Polyelectrolytes 345 Sujun Hu, Chengmei Zhong, Hongbin Wu, and Yong Cao 11.1 Introduction 345 11.2 Polymer Light–Emitting Devices Based on Water/Alcohol–Soluble Conjugated Polymers and Conjugated Polyelectrolytes 345 11.2.1 PLEDs Based on Emissive Water/Alcohol–Soluble Conjugated Polymers and Conjugated Polyelectrolytes 345 11.3 Water/Alcohol–Soluble Conjugated Polymers as Efficient Electron Injection/Transport Layer in PLEDs 350 11.3.1 Neutral WSCPs and Their Quaternized Polyelectrolyte Derivatives as EIL/ETL in Multiple Layer PLEDs 350 11.3.2 Water/Alcohol–Soluble Conjugated Polyelectrolytes as EIL/ETL in Multiple Layer PLEDs 359 11.3.3 Water/Alcohol–Soluble Conjugated Polymers and Conjugated Polyelectrolytes as Efficient EIL/ETL in WPLEDs 363 11.4 Water/Alcohol–Soluble Conjugated Polymers/Polyelectrolytes as Cathode Interlayer for Polymer Solar Cells 365 11.4.1 Water/Alcohol–Soluble Conjugated Polymers and Conjugated Polyelectrolytes as Cathode Interlayer for Conventional Device Structure 368 11.4.2 Water/Alcohol–Soluble Conjugated Polymers and Conjugated Polyelectrolytes as Cathode Interlayer for Inverted Device Structure 369 11.4.3 Role of the Cathode Interlayer Played in Improving PSC Performance 371 11.4.4 Water/Alcohol–Soluble Conjugated Polymers/Polyelectrolytes as Electron Donor Materials for Polymer Solar Cells 372 11.5 Applications of Water/Alcohol–Soluble Conjugated Polymers and Conjugated Polyelectrolytes in Other Optoelectronic Devices 373 11.5.1 Polymer Light–Emitting Electrochemical Cells 373 11.5.2 Dye–Sensitized Solar Cells 376 11.5.3 Organic Field Effect Transistors 380 11.6 Summary 381 11.7 Conclusion 382 References 382 12 Optical Processes in Conjugated Polyelectrolytes Dependence on Chain Conformation and Film Morphology 389 Giuseppina Pace and Richard Friend 12.1 Introduction 389 12.2 Hydrophobic and Electrostatic Interactions in CPEs 391 12.3 Amphiphilic CPEs and CPE–Surfactant Complexes: toward Ordered Structures and Controlled Photophysics at the Solid State 393 12.4 Photoluminescence Quenching in CPEs: Fast Exciton Dynamics 397 12.5 Effect of the Ion and Counterion Choice on the CPE Photoluminescence 400 12.6 Nature of the Excited States: Charge–Transfer States and Polarons in CPEs 404 12.7 Conclusions 407 References 408 Index 411

Bin Liu is Associate Professor in the Department of Chemical and Biomolecular Engineering, National University of Singapore (NUS). Her research focuses on the development of water–dispersable conjugated polymers with explorations on their sensing, imaging and device applications. She has over 130 scientific publications and has received several awards including the NUS Young Investigator Award, Singapore National Science and Technology Young Scientist Award and L’Oreal–Singapore Women in Science National Fellowship. Guillermo C. Bazan is Professor of Chemistry and Biochemistry at the University of California, Santa Barbara. He has over 300 publications and an H–index of 72. Much of his work is centered on the applications of conjugated polyelectrolytes in biosensing technologies and the fabrication of optoelectronic devices. Guillermo Bazan’s awards and recognitions include the 2006 ACS Cope Scholar Award, the 2005 Bessel Award and the 2003 National Science Foundation Special Creativity Award. In addition, he serves as a member of the editorial advisory boards of Macromolecules and Advanced Materials.