Peter C. Eklund Apparao M. Rao (Eds.)

Fullerene Polymers and Fullerene Polymer Composites

With 224 Figures and 19 Tables

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Contents

1. Fundamental Properties of Fullerenes M.S. Dresselhaus, G. Dresselhaus 1

1.1 Introduction to Fullerenes as Polymerie Materials and Composites 1 1.1.1 Historical Background to Fullerenes 1 1.1.2 Historical Background to Fullerene Polymers

and Fullerene-Polymer Composites 3 1.2 Structural Properties of Fullerene Molecules 3

1.2.1 Structure of CÖO 3 1.2.2 Structure of C70 and Higher Mass Fullerenes 6 1.2.3 Structure of Metallofullerenes 7

1.3 Synthesis 7 1.4 Structure in Condensed Phases 8

1.4.1 Crystalline C60 9 1.4.2 Crystalline C70 11 1.4.3 Crystalline Phases for Higher Mass Fullerenes 11 1.4.4 Intercalated Fullerene Structures 12

1.5 Polymerized Fullerenes 14 1.5.1 Photopolymerization of Ceo 15 1.5.2 Electron Beam-Induced Polymerization of Ceo 17 1.5.3 Pressure-Induced Polymerization of CÖO 17 1.5.4 Plasma-Induced Polymerization of CÖO 18 1.5.5 Photopolymerization of C70 Films 18

1.6 Vibrational Properties 19 1.6.1 Infrared-active Modes in Ceo 21 1.6.2 Raman-active Modes in Cßo 21 1.6.3 Silent Modes in C60 24 1.6.4 Vibrational Spectra for C70 24 1.6.5 Vibrational Modes in Doped Fullerene Solids 24 1.6.6 Vibrational Properties of Phototransformed Fullerenes . . . . 27

1.7 Electronic Properties 31 1.8 Optical Properties 35

1.8.1 Introduction to Molecular Photophysics 35 1.8.2 Optical Transitions in Photopolymerized Cßo 44

VIII Contents

1.9 Transport and Photoconductivity 46 1.9.1 Electrical Conductivity 46 1.9.2 Photoconductivity 48

1.10 Superconductivity 52 1.11 Concluding Remarks 57 References 58

2. Introduction to Electronic, Optical, and Transport Properties of Conducting Polymers and Fullerene-Polymer Composites P.A. Lane, Z.V. Vardeny 69

2.1 Introduction 69 2.2 Electronic States in Conducting Polymers 69 2.3 Absorption Studies of Conducting Polymers 76 2.4 Excited State Optical Studies 79 2.5 Optical Studies of t ^ C H ) , 81 2.6 Optical Studies of Polythiophene 84 2.7 Optical Properties of Cßo: Polymer Composites 89 2.8 Transport Properties of Conducting Polymers 91 2.9 Device Applications of Conducting Polymers 94 2.10 Summary 97 References 98

3. Supramolecular Photophysics and Photovoltaic Devices of Pullerene-Conjugated Polymer Composites N.S. Sariciftci 101

3.1 Introduction 101 3.1.1 Semiconducting, Conjugated Polymers

as Photoexcited Electron Donors 101 3.1.2 Buckminsterfullerene, C6o, as Electron Acceptor 102

3.2 Experimental Results: Ultrafast, Reversible, Photoinduced Electron Transfer in Conjugated Polymer/Fullerene Composite Films 104 3.2.1 Linear Absorption and Photoluminescence 104 3.2.2 Near Steady State Photoinduced Absorption 107 3.2.3 Sub-Picosecond Photoinduced Absorption 111 3.2.4 Sub-Picosecond Photoinduced Dichrosim 120 3.2.5 Steady State Infrared Photoinduced Absorption 123 3.2.6 Sensitization of Photoconductivity 124 3.2.7 Direct Experimental Evidence for the Metastable Charge

Separation: Light Induced Electron Spin Resonance (LESR) 127

3.3 Effect of the Surrounding Medium: Solution Studies 129

Contents IX

3.4 Photovoltaic and Photodetector Applications: A Molecular Approach to High Emciency Photovoltaic Cells Using Photoinduced Electron Transfer 130 3.4.1 Conjugated Polymer/Cßo Heterojunction Photodiodes . . . . 131 3.4.2 Diodes Made of Conjugated Polymer Composites

with a Network of Internal Heterojunctions 135 3.5 Future Areas 139 References 140

4. Optical Studies of Covalently Linked C 6 0 Solids A.M. Rao, P.C. Eklund 145

4.1 Introduction 145 4.2 Pristine C60 147 4.3 Vibrational Modes of Solid C60 149 4.4 Polymerized C6o Structures 152

4.4.1 Photopolymerized Ceo 153 4.4.2 Charge Transfer Excitons: a Possible Trigger Mechanism

for Photopolymerization 163 4.4.3 Theoretical Predictions 165 4.4.4 Experimental Evidence for CT Excitons in Ceo 166

4.5 Photo-induced Hardening of C60 Crystals 168 4.6 Pressure-induced Ceo Polymers 169 4.7 MiC6 0 Polymers 178

4.7.1 Na4C60 Polymer 180 References 182

5. First-Principles Molecular Dynamical Studies of Polymerized Cßo G.B. Adams, J.B. Page 185

5.1 Method: First-Principles Quantum Molecular Dynamics 185 5.2 Simulation One: Polymerized Ceo 188

5.2.1 Structure and Energy 188 5.2.2 Vibrational Properties 197 5.2.3 Electronic Eigenvalues 210 5.2.4 Energy Barrier to Dimer Separation 212 5.2.5 Summary for Photopolymerized Cßo 213 5.2.6 Other Forms of Polymerized Ceo 215

5.3 Simulation Two: C n 9 216 5.3.1 Predicting the Structure 216 5.3.2 Properties of the Predicted Structure 219 5.3.3 Summary for Cng 222

References 224

X Contents

6. Covalent Bonding Between Pullerenes M. Menon, K.R. Subbaswamy 229

6.1 Introduction 229 6.2 Theoretical Methods 230 6.3 Covalent Bonding Between Fullerenes 230

6.3.1 C60 Dimer 230 6.3.2 C70 Dimer 235 6.3.3 Curvature Dependence of Covalent Bonding 238 6.3.4 Summary 238

References 239

7. Polymerized Fullerite Structures: Experiment and Theory M. Nüiiez-Regueiro, L. Marques, J.L. Hodeau, C.H. Xu, G.E. Scuseria . 241

7.1 Introduction 241 7.2 Bonding Under Pressure 242

7.2.1 Organic Molecules Under Pressure 242 7.2.2 Carbon Under Pressure and New Possible

Carbon Structures 243 7.2.3 C60 Under Pressure 244 7.2.4 Polymerizing C60 246 7.2.5 C60 Dimers 247

7.3 The Polymerized Fullerite Structures 250 7.3.1 1-D Polymers 251 7.3.2 2-D Polymers 255 7.3.3 3-D Polymers 257

7.4 Conclusions 260 References 261

8. Polymerization of Charged Ceo Molecules H. Kuzmany, J. Winter 265

8.1 Introduction 265 8.2 Phases of AC60, A = K, Rb, Cs 266

8.2.1 Phase Separation Versus Structural Phase Transition to the Orthorhombic Phase for ACeo 267

8.2.2 Structure of the Polymerie Phase 271 8.3 Physical Properties of the Polymerie Phases 274

8.3.1 Vibrational Spectra and Optical Transitions 274 8.3.2 Magnetic Resonance 283 8.3.3 Transport 287

8.4 Electronic Structure of AC60 289 8.5 Stability Versus Atmospheric Conditions 291 8.6 Dimeric Phases and Annealing After Quenching of ACÖO 292

Contents XI

8.7 Other Polymerie Forms of C60 Füllendes 295 8.8 Summary and Open Questions 297 References 299

9. Electronic Structures and Optical Excitations in Ceo-Polymers K. Harigaya 303

9.1 Introduction 303 9.2 Models 307 9.3 Polarons in an Isolated Ceo Molecule 310 9.4 Doping Effects and Metal-Insulator Transition

in One-Dhnensional C60-Polymers 312 9.5 Metallic and Insulating States in Two-Dimensional Ceo-Polymers 318 9.6 Magnetism in One-Dimensional Ceo-Polymers 320 9.7 CT-Excitons in Ceo-Dimers and Polymers 325 9.8 Summary 329 References 330

10. Superconductivity of "Fullerene Conducting Polymer" Composites Doped by Alkali Metals A.A. Zakhidov, H. Araki, K. Yoshino 333

10.1 Introduction 333 10.2 Charge Transfer Processes in Pristine CP-Ceo Composites 335 10.3 Models of Cßo-Induced Superconductivity

and Role of Granularity 337 10.4 Low Field Microwave Absorption (LFMA)

in Superconducting CP(C6o)1)Aa; 341 10.4.1 Basics of LFMA as a Sensitive Test for Superconductivity . 341 10.4.2 Features of Superconducting LFMA

in PAT-C60-K and OO-PPV-C60-K 343 10.4.3 Low C60 Concentration y < 0.005 343 10.4.4 Intermediate to High C60 Concentration 0.01 < y < 0.1 . . . 346

10.5 SQUID Magnetometry 356 10.6 General Discussion 357

10.6.1 Paths of Electron Transfer and SC Phases 357 10.6.2 Prospects for Ceo-Induced Superconductivity 361

10.7 Conclusions 364 References 365

11. Solution-State Syntheses of Fullerene-Based Pendant, Pearl Chain, and Dendritic Polymers M.S. Meier 369

11.1 Introduction 369

XII Contents

11.2 Attachment of Fullerenes to Existing Polymers: Charm Bracelet Polymers 370

11.3 Pearl Necklace Polymers 379 11.4 Highly-Crosslinked Polymers 384 11.5 Others 385 11.6 Future Directions 386 References 386

Index 389