Eduard ZenkevichChristian von Borczyskowski

edited by

Self-Assembled Organic-Inorganic

NanostructuresOptics and Dynamics

Self-Assembled Organic-Inorganic

Nanostructures

for the WorldWind PowerThe Rise of Modern Wind Energy

Preben MaegaardAnna KrenzWolfgang Palz

editors

Eduard ZenkevichChristian von Borczyskowski

edited by

Self-Assembled Organic-Inorganic

NanostructuresOptics and Dynamics

Published by

Pan Stanford Publishing Pte. Ltd.Penthouse Level, Suntec Tower 3 8 Temasek Boulevard Singapore 038988 Email: editorial@panstanford.com Web: www.panstanford.com

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

Self-Assembled Organic-Inorganic Nanostructures: Optics and Dynamics

Copyright © 2016 Pan Stanford Publishing Pte. Ltd.

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ISBN 978-981-4745-43-7 (Hardcover)ISBN 978-981-4745-44-4 (eBook)

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Contents

Preface xvAcknowledgments xix

1. StructuralandEnergeticDynamicsinQuantumDot–DyeNanoassemblies 1

Eduard Zenkevich and Christian von Borczyskowski

1.1 Introduction 1 1.1.1 QD Surface Properties and Interface

Phenomena 3 1.1.2 Formation Strategies for QD–Dye

Nanoassemblies 7 1.1.3 Verification of QD Photoluminescence

Quenching in QD–Dye Nanoassemblies 14 1.2 Self-Assembly of Semiconductor Quantum

Dots and Functionalized Dye Molecules 20 1.2.1 Interacting Subunits and Self-Assembly

Approach 21 1.2.2 Nanoassemblies Based on Quantum

Dots and Porphyrin Molecules 22 1.2.2.1 Comparative titration experiments

and nanoassembly formation 22 1.2.2.2 Conditions for nanoassembly

formation 28 1.2.2.3 Quantitative studies of QD PL

quenching and porphyrin fluorescence sensitization in QD–porphyrin nanoassemblies 41

1.2.3 Nanoassemblies Based on QDs and Perylene Diimide Molecules 45

viii Contents

1.2.3.1 Nanoassembly formation and manifestation of surface-related and temperature effects 45

1.2.4 Role of the Solvent Polarity in Competition between FRET and Non-FRET Quenching Processes for QD PL in Nanoassemblies 52

1.3 Single Nanoassembly 61 1.3.1 Quantum Dot Blinking Statistics in

QD–Porphyrin Nanoassemblies 61 1.3.2 PL Quenching, Geometry of Nanoassemblies

and Conformational Stability of PDI Molecules on QD Surfaces 63

1.3.3 Time Dependent Fluctuations of FRET in Single QD–Dye Nanoassemblies 70

1.4 Quantitative Analysis of Non-Radiative Relaxation Pathways for Quantum Dots in Nanoassemblies 75

1.4.1 QD PL Quenching via Foerster Resonant Energy Transfer in QD–Dye Nanoassemblies 76

1.4.2 Size-Dependent Non-FRET QD PL Quenching in QD–Dye Nanoassemblies 90

1.4.3 Competition of FRET and Non-FRET Processes 99

1.4.4 Tuning Quantum Dot Electronic States and Exciton Relaxation Dynamics by One Attached Dye Molecule 106

1.5 Conclusions 123

2. InterrelationofAssemblyFormationandLigandDepletioninColloidalQuantumDots 149

Danny Kowerko

2.1 Introduction 150 2.2 Experimental Methods 152 2.2.1 Bulk Fluorimetry of QDS, PBI Molecules

and QD-PBI Assemblies 152 2.2.2 Single-Molecule Spectroscopy 153 2.3 Data Analysis 154

ixContents

2.3.1 Software and Gauss-Fit Based Analysis 154 2.3.2 Extracting PL Decay Rates and Electronic

States from PL Lifetime–Intensity Distributions 154

2.3.2.1 Monoexponential PL lifetime distributions 155

2.3.2.2 Multi-exponential PL lifetime distributions 157

2.4 Surface-Chemistry of Quantum Dots Studied at the Ensemble and Single-Molecule Level 167

2.4.1 Ensemble Spectroscopy of CdSe/ZnS Quantum Dots 168

2.4.1.1 Ligand depletion and spectral heterogeneity revealed by spectroscopy of diluted CdSe/ZnS QDs 168

2.4.1.2 Non-FRET type PL quenching and spectral blue shifts of CdSe/ZnS QD-dye assemblies 171

2.4.1.3 PL lifetime analysis of diluted CdSe/ZnS QDs 175

2.4.2 Single-Molecule and Single-Particle Spectroscopy 177

2.4.2.1 PL lifetime–intensity relations of single quantum dots 178

2.4.2.2 Correlation of intensity and spectral fluctuations indicates the quantum confined Stark effect 183

2.4.2.3 Photo-oxidation of single CdSe/ZnS QDs investigated by time-resolved single-molecule spectroscopy 184

2.4.2.4 Non-FRET PL quenching in single QD-dye assemblies 187

2.4.3 Comparison of Surface-Related Photophysical Phenomena of Ensemble and Single-Particle Experiments 189

2.5 Conclusion 193

x Contents

3. FluorescenceQuenchingofSemiconductorQuantumDotsbyMultipleDyeMolecules 201

Thomas Blaudeck

3.1 Introduction 201 3.2 Theory of Acceptor Redistribution in

Heteroaggregates 202 3.2.1 Fluorescence Quenching 202 3.2.2 Evaluation of Photoluminescence

Quenching Experiments and Modified Stern–Volmer Formalism 203

3.2.3 Derivation of the Photoluminescence Quantum Yield of a Donor in Presence of Multiple Acceptors 203

3.2.4 Case Study: A Donor with Quasi-Infinite Numberof Binding Sites 206

3.2.5 Case Study: A Donor with a Finite Number of Binding Sites 208

3.3 Application of the Redistribution Model to Experiments 209

3.4 Conclusion 211

4. StaticandDynamicQuenchingofQuantumDotPhotoluminescencebyOrganicSemiconductorsandDyeMolecules 215

Ines Trenkmann, Thomas Blaudeck, and Christian von Borczyskowski

4.1 Introduction 215 4.2 Experimental 216 4.3 Results and Discussion 217 4.3.1 Decrease of Photoluminescence with

Observation Time 217 4.3.2 Stern–Volmer Formalism for

Photoluminescence Quenching 220 4.3.3 Photoluminescence Intensity as a Function

of TPD Concentration 223

xiContents

4.3.4 Photoluminescence Decay Time as a Function of TPD Concentration 226

4.3.5 Deconvolution of Static and Dynamic PL Quenching 228

4.3.6 Ligand-Replacement Model for PL Quenching 230

4.3.7 Static and Dynamic PL Quenching by Functionalized Porphyrin Molecules 233

4.4 Conclusion 238

5. SelectedApplicationsofQDsandQD-BasedNanoassemblies 245

Eduard Zenkevich and Christian von Borczyskowski

5.1 Introduction 245 5.2 A Brief Overview of the Early History of QDs

Applications 248 5.3 Semiconductor Nanostructures for Solar Cells

and Photovoltaics 252 5.4 Singlet Oxygen Generation and Biomedical Aspects

for Semiconductor Quantum Dots and Their Bioconjugates 258

5.5 Quantum Dot-Based Nanoassemblies in Sensing, Imaging, and Diagnostics 264

5.6 Super-Resolution Microscopy with Quantum Dots 271 5.7 Conclusions 276

6. NanolithographyandDecorationofGeneratedNanostructuresbyDyeMolecules 295

Harald Graaf and Thomas Baumgärtel

6.1 Introduction 295 6.2 Silicon Oxide Nanostructures on Alkyl-Terminated

Silicon Surfaces 297 6.3 Attachment of CdSe-Nanocrystals on

Alkyl-Terminated Silicon 303

xii Contents

6.4 Attachment of Charged Dye Molecules 307 6.4.1 Attachment of Rhodamine 6G and Cresyl

Violet to the LAO Oxide Structure 308 6.4.2 Attachment of a Spermine-Functionalized

Perylene Diimide Derivative to the LAO Oxide 316

6.4.2.1 Optical emission at room temperature 318

6.4.2.2 Optical emission at low temperature 320

6.4.2.3 Fluorescence life time investigations 325

6.5 Covalent Attachment of FITC 337 6.6 Conclusion 342

7. IdentificationofHeterogeneousSurfacePropertiesviaFluorescentProbes 353

Daniela Täuber and Christian von Borczyskowski

7.1 Introduction 353 7.2 Impact of Chemical Inhomogeneities of

SiO2 Surfaces 355 7.2.1 Optical Decoration of Silanol Groups 355 7.2.2 Influence of Surface Inhomogeneities on

Diffusion Dynamics in Ultrathin Liquid Films 358

7.3 Decorating Charged Si Nanoparticles with Charge-Sensitive Dye Molecules 362

7.4 Conclusion 366

8. SelectiveSurfaceBindingofDyeMoleculesonHybridHumiditySensors 371

Ines Trenkmann

8.1 Introduction 371 8.2 Experimental 374 8.3 Results 375

xiiiContents

8.3.1 Analysis of the As-Prepared Hybrid Structures 375

8.3.2 Analysis of Rhodamine-Functionalized Hybrid Structures 380

8.4 Discussion 382

Index 385

Preface

The current state and perspectives in sciences are strongly linked to the development of novel complex materials as well as to the availability of sophisticated state-of-the-art experimental tools that enable the investigation and manipulation of the objects at various levels of organization, including single nanoobjects and biological sub-structures. The combination of organic and inorganic materials promises to make use of advantages of both types of materials, e.g., downsizing inorganic materials to the nanoscale (as is typical for state-of-the-art devices) and, e.g., nearly unlimited synthesis of functional organic compounds (even mimicking biologically relevant entities). Of special interest are those organic/inorganic entities that are formed due to self-assembly offering chemically specific and versatile formation routes according to the concepts of supramolecular chemistry. Due to the high functionality of such self-assembled nanostructures, applications are readily envisaged or already realized in nanosensorics, bio-medical applications, and photovoltaics. Recent advancements in nanotechnology permit to produce a variety of functional colloidal semiconductor quantum dots (QDs) and QD-based nanomaterials with unique optical and physico-chemical properties which are principally different from those of bulk materials of the same composition. Science and technology of QDs and QD-based nanomaterials have to deal with (on every length scale, from the molecular to the macro) surface and interfacial phenomena that can be tuned by varying the surface and interfacial energy and by changing the specific chemical interactions with organic compounds attached to such surfaces and interfaces. It means that namely the surface chemistry related to organic/inorganic interactions plays the principal role in the formation of optical properties of QDs and QD-based nanomaterials as well as may be considered as gateway to their possible applications in optoelectronic devices and nanosensors and as optical labels and drug carriers in biomedicine.

xvi

An alternative approach to inorganic/organic self-assembled structures on the nanoscale is to scale down inorganic substrates via nanolithography resulting in functionalized nanostructures or to even make use of inherent chemical heterogeneities of an inorganic surface. Again, in both cases appropriate organic molecules self-assemble on such “artificial” or “natural” nanostructures. In a recent Monograph, Tuning Semiconducting and Metallic Quantum Dots: Spectroscopy and Dynamics, we described the optical properties and photophysics of quantum dots concentrating on interfaces/surfaces and the perspectives of tuning the energies of electronic states and related dynamics. Basically, the present book provides a comprehensive description of the morphology and main physico-chemical properties of QD–dye self-assembled nanostructures and natural or lithographically generated surface inhomogeneities (with focus on results, including even some unpublished ones, obtained in our groups within the past decade, as well as some applications in the field of nanotechnology. It crosses disciplines to examine essential nanoassembly principles of inorganic nanostructures with organic molecules, excited state dynamics in nanoobjects, theoretical models, and methodologies. We show that upon nanoassembly formation, photochemical processes occurring at the interface between inorganic nanostructures and functionalized organic molecules and/or bio-objects are complex and may yield new and unexplored phenomena. Additionally, we discuss what parameters may control the photochemical and optical properties of such structures upon attachment of functionalized moieties and how such attachment onto the respective surface proceeds. Especially, we describe a solid base for the application of QD–dye based nanoassemblies in various fields of nanotechnology and biomedicine. Organized into eight chapters, the book begins with Chapter 1, titled “Structural and Energetic Dynamics in Quantum Dot–Dye Nanoassemblies,” which describes the results of basic research concerning formation principles and energetic dynamics in heterogeneous organic-inorganic QD–dye nanoassemblies, based on CdSe QDs and various dye molecules. Using a combination of ensemble (steady-state and time-resolved technique in a temperature range 77–295 K) and single-molecule spectroscopy

Preface

xvii

of QDs and nanoassemblies, we show that single functionalized dye molecules act as extremely sensitive probes for studying the complex interface physics and exciton relaxation processes in QDs. Our findings discussed here and in Chapters 2 (Interrelation of Assembly Formation and Ligand Depletion in Colloidal Quantum Dots), 3 (Fluorescence Quenching of Semiconductor Quantum Dots by Multiple Dye Molecules), and 4 (Static and Dynamic Quenching of Quantum Dot Photoluminescence by Organic Semiconductors and Dye Molecules) show that surface-mediated processes dictate the probability of several of the most interesting and potentially useful photophysical phenomena observed for colloidal QDs. In fact, Förster resonance energy transfer (FRET), charge transfer, and non-FRET processes are the main reasons for QD photoluminescence quenching in QD–dye nanoassemblies. We have succeeded to quantitatively clarify that the major part of the observed QD photoluminescence quenching in QD–dye nanoassemblies, namely non-FRET processes, can be understood, on one hand, in terms of electron tunneling beyond the CdSe core under conditions of quantum confinement and, on the other hand, by the influence of ligand dynamics. Such a comparative approach is presented in this book for the first time. Chapter 5, titled “Selected Applications of QDs and QD-Based Nanoassemblies,” lists a brief history of QD applications as well as representative selected examples of how QDs and QD-based nanomaterials can be applied in photovoltaics, sensing, biomedicine and sub-diffraction imaging (the last one together with single molecule detection was awarded by the 2014 Nobel Prize in Chemistry). Chapters 6 (Nanolithography and Decoration of Generated Nanostructures by Dye Molecules), 7 (Identification of Hetero-geneous Surface Properties via Fluorescent Probes), and 8 (Selective Surface Binding of Dye Molecules on Hybrid Humidity Sensors) are devoted to the description of the interaction of dye molecules with lithographically generated or “natural” surface inhomogeneities with dye molecules. The bibliography at the end of each chapter contains numerous leading papers, recent reviews, and books in which the readers will find specific references relevant to their subjects of interest.

Preface

xviii

Concluding, this book links interdisciplinary fundamental research (including lithography, surface chemistry, photochemistry of semiconductor QDs, and QD–dye nanoassembly formation), and selected perspectives for applications of QD–dye nanoassemblies and other organic/inorganic nanostructures. It offers an overview for graduate students, academics, researchers, and industry professionals, and anyone interested in this interdisciplinary field of nanomaterials.

EduardZenkevichMinsk, Belarus

Christian von BorczyskowskiChemnitz, Germany

September 2016

Preface