Control of the long-range self-organization of polycyclic aromatic hydrocarbons for device applications [Elektronische Ressource] / Wojciech Pisula

Pisula

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2005
• Nombre de lectures: 4
• Langue: English
• Poids de l'ouvrage: 14 Mo

Extrait

Control of the Long-Range
Self-Organization of Polycyclic Aromatic
Hydrocarbons for Device Applications







Dissertation zur Erlangung des Grades
“Doktor der Naturwissenschaften”

am Fachbereich Chemie und Pharmazie
der Johannes Gutenberg-Universität in Mainz



Wojciech Pisula
geb. in Cieplice Slaskie Zdroj
Mainz 2005


















Tag der mündlichen Prüfung: 28.09.2005


II

















III Contents

Contents

Introduction........................................................................................................................................1
Chapter 1 Supramolecular Organization of Discotic Liquid Crystals......................................6
1.1. Discotic Liquid Crystals............................................................................................................ 6
1.2. Mechanism of the Charge Carrier Transport ........................... 11
1.3. Electronic Devices based on Organic Matierials ................................................ 12
1.4. Homeotropic Alignment ................................................................................. 14
1.5. Alignment Techniques ........................................................... 16
1.5.1. Single Crystal Growth.............................................................................. 16
1.5.2. Vacuum Deposition.......................................................................................................... 16
1.5.3. Simple Solution Processing ..................................................................... 17
1.5.4. Langmuir-Blodgett Technique...................................................................... 18
1.5.5. Epitaxy Growth on PTFE Alignment Layers................................................................... 20
1.5.6. Alignment from the Isotropic Phase ............ 22
1.5.7. Alignment from Solution along a Concentration Gradient.............................................. 23
1.6. Alignment of HBC molecules.............................................................................. 23
Chapter 2 Materials and Alignment Techniques..............................................27
2.1. Materials.................................................................................................................................. 27
2.2. Zone Processing Methods ............................................................................... 31
2.2.1. Filament Extrusion................................................................................... 32
2.2.2. Zone-casting..................................................................................................................... 33
2.2.3. Zone-crystallization ........................................................ 36
Chapter 3 Relation between the Molecular Architecture and the Supramolecular
Organization in Bulk..............................................................................................................38
IV Contents
3.1. Relationship between Core Size, Side Chain Length and the Supramolecular
Organization in the Hexagonal Mesophase.......................................................................... 38
3.2. Investigation of the Supramolecular Structure of Dove-Tailed HBCs ................................... 52
3.2.1. Alkyl Side Chains with Branching at the β-position .................................... 52
3.2.2. Branched Side Chains bearing Ether Linkages........................................ 61
3.3. Examples for pronounced Supramolecular Order................................................ 67
3.4. Control of the Superperiodicity along Columnar Structures .......................... 71
3.4.1. Hexa-peri-hexabenzocoronenes.................................................................... 72
3.4.2. Extended Aromatic Cores of C96 ................................... 85
Chapter 4 Self-organization in Solution and in Solution Processed Thin Films....................87
4.1. Solution Processing of Crystalline Hexa-peri-hexabenzocoronenes ................... 88
4.1.1. Hexakis-dodecyl-hexa-peri-hexabenzocoronene ............................................................. 88
4.1.1.1. Self-Aggregation in Solution and in Drop-Cast Films of HBC-C ...... 88 12
4.1.1.2. Zone-casting of HBC-C .......................................................................................... 91 12
4.1.2. Dove-Tailed Hexa-peri-hexabenzocoronenes................................................................ 123
4.2. Solution Processing of Non-Crystalline Discotics................. 129
Chapter 5 Control of the Thermal Behavior and Processing from the Isotropic Phase .....141
5.1. Control of the Isotropization Temperature by the Introduction of Dove-Tailed Side
Chains ................................................................................................................................. 141
5.2. Morphology Formation (edge-on arrangement) during Crystallization from the
Isotropic Phase of Alkyled HBCs....................................................................................... 145
5.2.1. Processing from the Isotropic Phase ....................................................... 154
5.2.1.1. Zone-crystallization ................................................................................................ 154
5.2.1.2. Effect of the Curvature on the Self-organization from the Isotropic Phase............ 157
5.3. Control of the Thermal Behavior by Asymmetrical Substitution and the Zone-
crystallization of “unwrapped” HBC.................................................................................. 161
5.4. Control of the Homeotropic Alignment of HBCs......................................... 169
5.4.1. HBCs substituted by Dove-Tailed Side Chains with Ether Linkages............................ 170
V Contents

5.4.2. Homeotropic Alignment of All-Hydrocarbon HBCs..................................................... 178
5.4.3. Binary Mixtures of Discotics with Different Molecular Architecture.......... 187
5.4.4. Outlook for TOF Measurements on Homeotropically Aligned Samples ...................... 197
Conclusions.....................................................................................................................................200
Experimental Appendix.........................................................................................202
References .......................................................................................................................................205
List of Publications & Presentations..........................................................................................223














VI
Index of Abbreviations
AFM atomic force microscopy
CD circular dichroism
DSC differential scanning calorimetry
FET field-effect transistor
FFT fast Fourier transformation
g gram
HBC hexa-peri-hexabenzocoronene
HDMS hexamethyldisilazane
HOPG highly oriented pyrolytic graphite
HR-TEM high-resolution transmission electron microscopy
ITO indium-tin oxide
LB Langmuir-Blodgett
LC liquid crystal
LED light emitting diode
NMR nuclear magnetic resonance
POM polarized optical microscopy
PAH polycyclic aromatic hydrocarbons
Pc phthalocyanine
PTFE poly(tetrafluoroethylene)
THF tetrahydrofuran
TOF time-of-flight
UV-Vis ultraviolet/visible
WAXS wide-angle X-ray scattering
XRD X-ray diffraction
VII




























VIII Introduction
Nowadays, people are surrounded by a variety of different and complex electronics with
integrated circuits which are established in plenty of areas. These electronics are integrated in
devices which are of essential importance for our daily life and improve substantially the
peoples standard of living. But due to the rapid technological progression and the introduction
of novel electronics, our close environment is exposed to permanent changes.
Most of the technology is based on metals and inorganic semiconductors. Undoubtedly,
these materials possess excellent conductive properties, but nevertheless other materials with
novel properties are intensively investigated which could fulfill the great demand for further
device miniaturization on the one hand and allow low cost production of these devices on the
other. Following these requirements organic materials appear to be currently the most
potential candidates for the partial replacement of metals and silicon in field-effect transistor,
light-emitting diodes or photovoltaic devices. Furthermore, organic semiconductors are very
promising due to their low cost and their easy processibility. Both academic and industrial
research p