Polymeric light harvesting antenna

99 Pages·2017·4.72 MB·English

Polymeric light harvesting antenna

Ronald Merckx

Promotor: Prof. Dr. Richard Hoogenboom
Guide: Dr. Eng. Valentin-Victor Jerca

Academic year 2016-2017

A dissertation submitted to Ghent University in partial fulfilment of the
requirements for the degree of Master of Science in Chemistry
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Acknowledgements
In the long run from middle school towards a job, a study at the university is one of the most
important and certainly the largest contribution towards both knowledge and self-
development. A master thesis should be the top of the bill of a 5 year long journey at the
university. In this road towards a Master degree in science, I personally learned a lot of things
about both myself and my skills in chemistry. The evolution I passed through would not have
been possible without certain persons I met along the way, by this short fragment, I would like
to express my gratitude towards these people.
My first resignation goes to Professor Dr. Richard Hoogenboom, whom made it possible that
I could pick and study a subject of my choice. Whenever I faced obstacles in my project both
practical and theoretical, he was able to provide the information that was needed to continue
the research in a so efficient manner as possible. I would also like to thank him for the
opportunity to be part of a most welcoming and friendly Supramolecular Chemistry group.
In this Supramolecular Chemistry group I would like to express my gratitude to someone in
particular, namely my supervisor dr. Valentin- Victor Jerca. Who was always very patient when
something went wrong due to my mistakes, but who was also very helpful when I did not
know how to continue. He helped me to develop and improve my practical skills. But also he
was not only my supervisor, he was more of very smart friend who was always there for a
joke, which created a very nice work environment.
Besides Victor I would like also to thank the other Supramolecular Chemistry group members
(Bart, Joachim, Maarten, Maji, Zhanyao, Xiaowen, Martin, Victor dlr, Ali, Annelore, Brynn,
Glenn and Mathias) and certainly the other thesis students (Willem, Ann, Maria, Wouter, Jana
and Tim) for contributing greatly to the pleasant atmosphere both outside and in the lab.
Additionaly I would like to thank Vincent and Jos from the professor Madder group for their
willingness to help me with various things in the lab.
Finally, I would like to thank my girlfriend and certain friends (Babs, Jasper, Chiel, Luca, Elke
and Philippe) for supporting me throughout the education and my thesis year. And last but
certainly not least I would like to thank my parents for the support. Without all these people
it would have not been possible to achieve this.
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Table of Contents
Abbreviations .......................................................................................................................................... 7
1. Introduction .................................................................................................................................... 9
1.1 Photophysical processes in nature ....................................................................................... 10
1.2 Chlorophyll, carotene and other pigments .......................................................................... 11
1.2.1 Absorption spectra ....................................................................................................... 11
1.2.2 Light harvesting processes and the reaction centre .................................................... 13
1.2.3 Energy transfer from the antenna to the reaction centre ........................................... 14
1.3 Synthetic light harvesting ..................................................................................................... 15
1.3.1 Light harvesting systems .................................................................................................. 15
1.3.1.1 Conjugated polymers .................................................................................................... 15
1.3.1.2 Dendrimers.................................................................................................................... 16
1.3.1.3 Side chain polymers ...................................................................................................... 17
1.4 Photophysical processes in light-harvesting polymers ....................................................... 18
1.4.1 Energy transfer mechanisms on the molecular scale ...................................................... 18
1.4.2 Energy transfer in light-harvesting polymers .................................................................. 20
1.4.2.1 Intermolecular energy transfer .................................................................................... 20
1.4.2.2 Intramolecular energy transfer .................................................................................... 21
1.4.2.3 Energy migration in light-harvesting polymers ........................................................... 22
1.4.2.4 The antenna effect in light-harvesting polymers......................................................... 23
1.5 Goal of the project ................................................................................................................ 26
2. Results and discussion .................................................................................................................. 28
2.1 Photophysical characterization of the starting fluorophores ............................................. 28
2.1.1 UV-Vis characterization ................................................................................................ 28
2.1.2 Steady state fluorescence spectroscopy ...................................................................... 29
2.2 Synthesis of dye–labeled poly-(2-ethyl-2-oxazoline)s ......................................................... 34
2.2.1 Synthesis of single-labeled poly-(2-ethyl-2-oxazoline)s .............................................. 34
2.2.2 Synthesis of α,-ω-dye-labeled poly-(2-ethyl-2-oxazoline)s ......................................... 38
2.3 Light harvesting antenna polymers based on (1-pyrenylpropyl)-2-oxazoline (PyOx) ........ 43
2.3.1 Synthesis route ............................................................................................................. 44
2.3.2 Energy transfer in pPyOx-PEtOx-Cou copolymers ....................................................... 47
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2.3.3 Energy transfer in pPyOx-PEtOx-Cou copolymers in film ............................................ 48
2.4 Light harvesting antennas based on poly-(2-isopropenyl-2-oxazoline) modified polymers
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2.4.1 Synthesis and characterization of poly-(2-isopropenyl-2-oxazoline) modified polymers
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2.4.2 Synthesis of the model compounds ............................................................................. 51
2.4.3 Energy transfer in PIPRO modified copolymers........................................................... 53
2.4.4 Energy transfer in modified PIPRO copolymers in film ............................................... 54
3. Conclusions & Outlook ................................................................................................................. 56
4. Appendix A .................................................................................................................................... 58
4.1 Materials ............................................................................................................................... 58
4.2 Equipment ............................................................................................................................. 58
4.3 Compound synthesis............................................................................................................. 61
4.3.1 Organic compounds ...................................................................................................... 61
4.3.2 Polymer synthesis ......................................................................................................... 65
6. References......................................................................................................................................... 72

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Abbreviations
ACN Acetonitrile
ATP Adenosine Triphosphate
BODIPY boron-dipyrromethene
CROP Cationic Ring Opening Polymerization
DCM Dichloromethane
DMF N, N-dimethylformamide
DMSO Dimethylsulfoxide
DP Degree of polymerization
EtOAc Ethyl acetate
FRET Förster Resonance Energy Transfer
HOMO Highest Occupied Molecular Orbital
LHC Light Harvesting Complex
LUMO Lowest Unoccupied Molecular Orbital
MeOH Methanol
MeOts Methyl p-toluenesulfonate
NADPH Nicotinamide adenine Sinucleotide Phosphate
NMR Nuclear magnetic resonance spectroscopy
PAH Polycyclic aromatic hydrocarbon
PEtOx Poly-(2-ethyl-2-oxazoline)
PIPRO Poly-(2-isopropenyl-2-oxazoline)
PMMA Poly-(methyl methacrylate)
PSU Photosynthetic Unit
PyOx 2-(3-(3,8-dihydropyren-1-yl) propyl)-4,5-dihydrooxazole
RPM Rotations per Minute
SEC (HFIP) Hexafluoroisopropanol Size Exclusion Chromatography
SOCl2 Thionyl chloride
TEA Triethylamine

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1. Introduction

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The world energy consumption is ca. 4,7 ∗ 10 J (450quadrillion Btu) and is expected to grow
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2% each year for the next 25 years. As the world population grows, the demand for natural
resources, in the form of energy increases, while the supply of coal, oil and gas drastically
decreases. Earth’s resources alone are not enough to cover this consumption, so the
anthropological impact should decrease or other sources need to be explored. Concerns about
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global warming have led to high interest in the field of renewable energy. In this area there
were numeral attempts to create energy in a green , more sustainable way (e.g. solar cells,
water and wind turbines, etc...)
In order to improve the existing solar cells, different paths have been explored. Recently,
several major advances have been made in the design of dyes and electrolytes for dye-
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sensitized solar cells. Further efforts, including metal-ligand complexes and other light
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harvesting systems were explored to improve solar cell performances. This master
dissertation will focus on light harvesting systems, more specific on light harvesting antenna’s.
Light harvesting and energy transfer processes of photosynthesis are the fastest and most
efficient known to mankind. In order for researchers to improve our light and energy
harvesting systems, gaining information and understanding about these processes is
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crucial. By doing so, one could find a clean and sustainable source of energy, which might
benefit society in an enormous way.

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1.1 Photophysical processes in nature
Photosynthesis, synthesis aided by light is one of the most important processes in plants, algae
and photosynthetic bacteria. In a process driven by light energy, glucose molecules (or other
sugars) are constructed from water and carbon dioxide, and oxygen is released as a byproduct.
The glucose molecules serve as fuel for cells: their chemical energy can be harvested through
processes like cellular respiration and fermentation which generates a compound named
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Adenosine Triphosphate (ATP). This chemical energy in the form of a molecule can be used
to energize other processes taking place in the organism.
The total photosynthetic reaction can be summarized as follows:
6𝐶𝑂2 + 6𝐻2𝑂 → 𝐶6𝐻12𝑂6 + 602
The photosynthetic process is split up in two steps: light and dark reactions. In green plants
the light reactions occur in the thylakoid membrane and convert the incoming sunlight into
molecules, and are thereby referred to as light dependent. In the stroma within the
chloroplast the dark reactions take place, where they convert carbon dioxide into 6 membered
sugar rings (Fig. 1). The adjective dark is added, because these reactions does not require light
to take place. ATP and NADPH (which are products originating the light reactions) are used to
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drive the dark reaction.

Figure 1. Light and dark reactions contributing to photosynthesis. (Source: Khan Academy)
The Calvin cycle is a biochemical pathway embedded in the dark reactions which uses carbon
dioxide, ATP and NADPH to form sugars. The first product formed in this cycle is a three carbon
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