Multichromophoric Arrays of Perylene Bisimide Dyes – Synthesis

237 Pages·2007·5.35 MB·English

Multichromophoric Arrays of
Perylene Bisimide Dyes – Synthesis
and Optical Properties

Dissertation zur Erlangung des
naturwissenschaftlichen Doktorgrades
der Bayerischen Julius-Maximilians-Universität Würzburg

vorgelegt von
Catharina Hippius
aus Jena

Würzburg 2007
Eingereicht am: _____________________
bei der Fakultät für Chemie und Pharmazie

1. Gutachter: _________________________________
2. Gutachter: _________________________________
der Dissertation.

1. Prüfer: _________________________________
2. Prüfer: _________________________________
3. Prüfer: _________________________________
des öffentlichen Promotionskolloquiums.

Tag des öffentlichen Promotionskolloquiums:
_________________________________

Doktorurkunde ausgehändigt am: ___________________________
List of Abbreviations

A (energy or electron) acceptor
Boc tert-Butyloxycarbonyl
CR charge recombination
CS charge separation
CT charge transfer
CV cyclic voltammetry/voltammogram
D (energy or electron) donor
EADS evolution associated difference spectra
ESI electro-spray ionization
FRET fluorescence resonance energy transfer
HOMO highest occupied molecular orbital
HPLC high pressure liquid chromatography
IRF instrument response function
LHS light-harvesting system
LUMO lowest unoccupied molecular orbital
MALDI matrix-assisted laser desorption injection
NIR near infrared
NP normal phase
PET photoinduced electron transfer
PBA perylene-3,4:9,10-tetracarboxylic acid bisanhydride (perylene bisanhydride)
PBI perylene-3,4:9,10-tetracarboxylic acid bisimide (perylene bisimide)
PMI perylene-3,4:9,10-tetracarboxylic acid monoanhydride monoimide (perylene
monoimide)
RT room temperature
SADS species associated difference spectra
TBAHFP tetrabutylammoniumhexafluorophosphate
TLC thin layer chromatography
UV ultraviolet
vis visible

Table of Contents

AIM OF THIS THESIS 1
CHAPTER 1 INTRODUCTION 11
1.1 Perylene Bisimides in Artificial Light-Harvesting Architectures 12
1.1.1 Linear Light-Harvesting Arrays 13
1.1.2 Light-Harvesting Molecular Square Assemblies 16
1.1.3 Dendritic Light-Harvesting Structures 17
1.2 Introduction to Calix[4]arenes 20
1.2.1 Definition and Nomenclature 20
1.2.2 Conformations of Calix[4]arenes 21
1.2.3 Functionalisation on the Wide Rim of Calix[4]arenes 24
1.3 Basic Concepts of Photoinduced Processes in Dye Arrays 26
1.3.1 Energy Transfer 26
1.3.1.1 Dexter Energy Transfer 27
1.3.1.2 Förster Energy Transfer 28
1.3.2 Electron Transfer 30
1.3.3 Optical Properties of Dye Aggregates 33
1.4 References 35

CHAPTER 2 INSTRUMENTATION AND EXPERIMENTAL METHODS 43
2.1 Time-Resolved Spectroscopy Measurements 44
2.1.1 Femtosecond Transient Absorption Measurements 44
2.1.2 Time-Resolved Fluorescence Measurements 45
2.2 Global and Target Analysis 47
2.3 Spectroelectrochemistry 48
2.4 Cyclic Voltammetry 49
2.5 References 49
CHAPTER 3 EXCITED STATE INTERACTIONS IN CALIX[4]ARENE–
PERYLENE BISIMIDE DYE CONJUGATES 51
3.1 Introduction 52
3.2 Synthesis and Structural Characterization 54
3.3 Optical Properties 56
3.4 Electrochemistry and Spectroelectrochemistry 60
3.5 Gibbs Energy of Photoinduced Electron Transfer 64
3.6 Femtosecond Transient Absorption Spectroscopy 66
3.7 Global and Target Analysis 69
3.8 Conclusions 78
3.9 Experimental Section 79
3.10 Appendix 88
3.11 References 93

CHAPTER 4 SEQUENTIAL FRET PROCESSES IN CALIX[4]ARENE-
LINKED ORANGE-RED-GREEN PERYLENE BISIMIDE DYE ARRAYS 99
4.1 Introduction 100
4.2 Synthesis and Structural Characterization 103
4.3 Molecular Structure 105
4.4 Temperature-dependent 1H NMR Studies 107
4.5 Optical Properties 109
4.6 Femtosecond Transient Absorption Spectroscopy 115
4.7 Global and Target Analysis 121
4.8 Conclusions 133
4.9 Experimental Section 134
4.10 Appendix 149
4.11 References 152
CHAPTER 5 PINCHED CONE EQUILIBRIA IN CALIX[4]ARENES BEARING
TWO IDENTICAL PERYLENE BISIMIDE DYES 161
5.1 Introduction 162
5.2 Synthesis and Structural Characterization 165
5.3 1H NMR Studies 168
5.4 UV/vis Absorption Properties 171
5.5 Temperature Dependent UV/vis Absorption Spectra 177
5.6 Steady State Fluorescence Emission Properties 180
5.7 Time-resolved Emission Spectroscopy 184
5.8 Electrochemistry 186
5.9 Femtosecond Transient Absorption Spectroscopy 188
5.10 Global and Target Analysis 191
5.11 Conclusions 194
5.12 Experimental Section 195
5.13 Appendix 200
5.14 References 206

CHAPTER 6 SUMMARY 213
CHAPTER 7 ZUSAMMENFASSUNG 219
DANKSAGUNG/ACKNOWLEDGEMENT 225
CURRICULUM VITAE 228
LIST OF PUBLICATIONS 229

Aim of this Thesis

Aim of this Thesis

The light-driven reactions of photosynthesis are the means by which nature converts
energy of light into a stable electrochemical potential, and accordingly, photosynthesis
represents one of the most important processes in biological systems. It has been
demonstrated that, for example, in purple bacteria in the early steps of photosynthesis the
light energy is absorbed by a network of so-called antenna pigment proteins and very
efficiently transported through energy transfer to the photochemical reaction center where
the energy is converted through a sequence of electron transfer reactions.1 Key requirement
for the high efficiency of this process is the defined organization of a multitude of
chromophores in space. Inspired by these biofunctional systems many organic chemists
aim at artificial structures containing multiple chromophores that provide sequential energy
transfer, but the realization of high efficiency and directionality remains a challenging task.
On the one hand, this is due to the synthetic challenge to position dyes at predefined spatial
positions and, on the other hand, competing processes like photoinduced electron transfer
may take place between photoexcited dyes located in close proximity.2 To date the
majority of covalent multichromophoric architectures showing efficient directional energy
transfer are either based on dendrimers3,4 (in general, with energy transfer from peripheral
chromophores to the core dye) or linear arrays of chromophores that are mostly linked by
rigid π−conjugated spacers.5,6
Numerous classes of functional dyes have been employed in multichromophoric
architectures among which, particularly, perylene bisimides (PBIs)7 became popular to
investigate the basic light-harvesting energy transfer processes.8 Perylene bisimides are
especially suitable for this purpose due to their bright photoluminescence with quantum
yields up to unity, chemical inertness, and exceptional photostability.7,9,10 Moreover,
perylene bisimides show excellent n-type semiconductivity,11 and have been applied
widely as industrial pigments, laser dyes,9,12 probes for single molecule spectroscopy,4a,13
organic thin film transistors,14 and solar cells.15 Recently, their ability to form
1
Aim of this Thesis

supramolecular light-harvesting architectures by π−π-stacking, hydrogen-bonding or
metal-ion-coordination has been explored.7,16,17
Calixarenes are supramolecular building blocks with distinct complexation capabilities
that are obtained from the condensation of formaldehyde with para-alkylphenols under
alkaline conditions.18 They usually consist of phenolic units that are separated by
methylene bridging groups. The name calix which means beaker in Latin and Greek was
suggested by the bowl- or beakerlike shape of the cyclic tetramer in the cone conformation.
Calixarenes are readily available in larger quantities by simple one-pot procedures19 and
are easily modified in various ways by reactions that can be independently carried out at
the narrow rim (the phenolic hydroxy groups) and at the wide rim (the aromatic positions
para to the phenolic hydroxy groups).18,19 Consequently, they represent an ideal scaffold
on which to assemble various desired functionalities such as nonlinear optical dyes,20
electrophores,21 and fluorophores.22 Calixarenes have been also used as versatile building
blocks for the construction of larger species through self-assembly by, for example,
hydrogen bonding,23 or metal-ion-coordination.24 A covalent linkage of calix[4]arenes with
perylene bisimides affords conjugates that combine the interesting properties of the
individual building blocks.25
Aim of this thesis was the synthesis of calix[4]arene functionalized perylene bisimide
dye arrays containing variate chromophoric units. Accordingly, a variety of multichromo-
phoric conjugates composed of up to three different types of perylene bisimide chromo-
phores (orange, red, and green PBIs) connected to each other by calix[4]arene spacers was
envisioned, as well as their monochromophoric reference compounds. The obtained conju-
gates should be characterized with respect to their photochemical properties and light-
harvesting ability by means of several steady state and time-resolved spectroscopic tech-
niques. In this context, a new design principle for artificial light-harvesting architectures
has been realized aiming at a zigzag-type of arrangements of perylene bisimide
chromophoric units (for details see Chapter 4) which is exemplified in the schematic
representation of a newly synthesized PBI-calix[4]arene light-harvesting array depicted in
Figure 1. Furthermore, PBI-Calix[4]arene arrays composed of identical chromophores
should be synthesized to elucidate intramolecular π−π-interactions of the PBI moieties.
2