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Supramolecular chemistry based on redox- active components and cucurbit[n]urils Samir Andersson Doctoral Thesis Stockholm 2010 Akademisk avhandling som med tillstånd av Kungl Tekniska Högskolan i Stockholm framlägges till offentlig granskning för avläggande av doktorsexamen i kemi med inriktning mot organisk kemi fredagen den 15 oktober kl 10.00 i sal F3, KTH, Lindstedtsvägen 26, Stockholm. Avhandlingen försvaras på engelska. Opponent är Professor Werner M. Nau, Jacobs University, Germany.

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Page 1: Supramolecular chemistry based on redox- active ...353246/FULLTEXT01.pdfSamir Andersson, 2010: Supramolecular chemistry based on redox-active components and cucurbit[n]urils, KTH Chemical

Supramolecular chemistry based on redox-

active components and cucurbit[n]urils

Samir Andersson

Doctoral Thesis

Stockholm 2010

Akademisk avhandling som med tillstånd av Kungl Tekniska Högskolan i Stockholm

framlägges till offentlig granskning för avläggande av doktorsexamen i kemi med

inriktning mot organisk kemi fredagen den 15 oktober kl 10.00 i sal F3, KTH,

Lindstedtsvägen 26, Stockholm. Avhandlingen försvaras på engelska. Opponent är

Professor Werner M. Nau, Jacobs University, Germany.

Page 2: Supramolecular chemistry based on redox- active ...353246/FULLTEXT01.pdfSamir Andersson, 2010: Supramolecular chemistry based on redox-active components and cucurbit[n]urils, KTH Chemical
Page 3: Supramolecular chemistry based on redox- active ...353246/FULLTEXT01.pdfSamir Andersson, 2010: Supramolecular chemistry based on redox-active components and cucurbit[n]urils, KTH Chemical
Page 4: Supramolecular chemistry based on redox- active ...353246/FULLTEXT01.pdfSamir Andersson, 2010: Supramolecular chemistry based on redox-active components and cucurbit[n]urils, KTH Chemical

Samir Andersson, 2010: Supramolecular chemistry based on redox-active

components and cucurbit[n]urils, KTH Chemical Science and Engineering,

Royal Institute of Technology, SE-100 44 Stockholm, Sweden.

Abstract

This thesis describes the host-guest chemistry between Cucurbit[7]uril (CB[7])

and CB[8] and a series of guests including bispyridinium cations, phenols and

napthalenes. These guests are bound to ruthenium polypyridine complexes or

ruthenium based water oxidation catalysts (WOCs). The investigations are

based upon utilizing the covalently linked photosensitizer and the electronic

effects and chemical processes are investigated.

The first part involves a careful study of the exited state for the Ruthenium

viologen dyad. It was shown that the complex could form a long-lived exited

state radical as well as a light driven formation of rotaxane.

The second part are based upon a charge-transfer system, investigating the

possible formation of a trimer inside the CB[8] utilizing viologen and a

ruthenium-phenol dyad.

The third part involves a study of a ruthenium photosensitizer and two

different viologen units, where a chemical- or light-driven process is used to

create a psuedorotaxane and a rotaxane.

The fourth part concerns the interactions between a napthol-viologen triad with

CB[7,8] and -CD.

The fifth part contains the investigation of CB[8] in a non-aqueous

environment. The viologen-CB[8] chemistry was investigated and a novel

template based synthesis was designed.

The sixth part is an investigation of water oxidation catalysts and the allosteric

mechanism of such compounds when encapsulated in a CB host. It was found

that the host could regulate the activity of the catalyst, depending on

placement.

Keywords: Cucurbit[n]uril; Molecular motor; Light driven; Water oxidation,

Redox-active; Viologen.

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Abbreviations

CB[n] Cucurbit[n]uril, where n=5, 6, 7, 8, 10

CT Charge-transfer

DHN Dihydroxynapthalene

WOC Water Oxidation Catalyst

OEC Oxygen Evolving Complex

Bpy 2,2'-bipyridine

Dba 2,2'-bipyridine-6,6'-dicarboxylic acid

MV2+

N,N-dimethyl-4,4’-bipyridinium (methylviologen)

V2+

N,N-R,R’-4,4-bipyridinium Viologen, R=alkyl chains

DMV2+

N,N-dimethyl-3,3’dimethyl-4,4’-bipyridinium

DV2+

N,N-R,R’-3,3’dimethyl-4,4’-bipyridinium, R=alkyl chains

DAP2+

Diazapyrenium

EC Electrochemistry

TEA Triethylamine

TEOA Triethanolamine

β-CD β-Cyclodextrin

TA Transient absorption

CV Cyclic voltammogram

LFTA Laser Flash Transient Absorption

Np Napthol

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List of Publications

This thesis is based on the following papers, referred to in the text by their

Roman numerals I-IX:

I. The photoinduced long-lived charge-separated state of Ru(bpy)3-

methylviologen with cucurbit[8]uril in aqueous solution

Shiguo Sun, Rong Zhang, Samir Andersson, Jingxi Pan; Bjorn

Åkermark and Licheng Sun

Chem. Commun. 2006, 40, 4195-4197

II. Host-guest chemistry and light driven molecular lock of Ru(bpy) 3-

viologen with cucurbit[7-8]urils

Shiguo Sun, Rong Zhang, Samir Andersson, Jingxi Pan; Bjorn

Åkermark and Licheng Sun

J. Phys. Chem. B, 2007, 111(47), 13357-63

III. Unusual partner radical trimer formation in a host complex of

cucurbit[8]uril, ruthenium(II) tris-bipyridine linked phenol and

methyl viologen

Shiguo Sun, Samir Andersson, Rong Zhang and Licheng Sun

Chem. Commun. 2010, 46(3), 463-465

IV. Selective positioning of CB[8] on two linked viologens and

electrochemically driven movement of the host molecule

Samir Andersson, Dapeng Zou, Rong Zhang, Shiguo Sun, Bjorn

Åkermark and Licheng Sun

Eur. J. Org. Chem. 2009, 8, 1163-1172.

V. Light driven formation of a supramolecular system with three

CB[8]s locked between redox-active Ru(bpy)3 complexes

Samir Andersson, Dapeng Zou, Rong Zhang, Shiguo Sun, Bjorn

Åkermark and Licheng Sun

Org. Biom. Chem. 2009, 7(17), 3605-3609

VI. Selective binding of cucurbit[7]uril and β-Cyclodextrin with a

redox-active molecular triad Ru(bpy)3-MV2+

-napthol

Dapeng Zou, Samir Andersson, Rong Zhang, Shiguo Sun, Bjorn

Åkermark and Licheng Sun

Chem. Commun. 2007, 45, 4734-4736

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VII. A host-induced intramolecular charge-transfer complex and light-

driven radical cation formation of a molecular triad with

cucurbit[8]uril

Dapeng Zou, Samir Andersson, Rong Zhang, Shiguo Sun, Bjorn

Åkermark and Licheng Sun

J. Org. Chem. 2008, 73(10), 3775-3783.

VIII. Isolated supramolecular Ru(bpy)3-viologen- Ru(bpy)3 complexes

with trapped CB[7,8] and photoinduced electron transfer study in

non-aqueous solution

Thitinun K. Monhaphol, Samir Andersson, and Licheng Sun

Manuscript

IX. An efficient water oxidation system based on a supramolecular

assembly of molecular catalyst and cucurbit[7]uril.

Samir Andersson and Licheng Sun

Manuscript

Paper not included in this thesis:

I. Synthesis, electrochemical, and photophysical studies of

multicomponent systems based on porphyrin and ruthenium(II)

polypyridine complexes

Xien Liu, Jianhui Liu, Jingxi Pan, Samir Andersson and Licheng Sun

Tetrahedron. 2007, 63(37), 9195-9205.

II. Chemical and Photochemical Water Oxidation Catalyzed by

Mononuclear Ruthenium Complexes with a Negatively Charged

Tridentate Ligand

Lele Duan, Yunhua Xu, Mikhail Gorlov, Lianpeng Tong, Samir

Andersson and Licheng Sun

Chem. Eur. J. 2010, 16(15), 4659-4668.

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Table of Contents

Abstract

Abbreviations

List of publications

1. Introduction ..................................................................................... 1 1.1. Supramolecular chemistry ..................................................................... 1 1.2. Cucurbit[n]uril ........................................................................................ 2

1.2.1. Synthetic studies ....................................................................................... 3 1.2.2. Inclusion complexes.................................................................................. 4 1.2.3. Molecular machines .................................................................................. 5 1.2.4. Catalysis of reactions and other improvements ......................................... 6 1.2.5. Drug delivery ............................................................................................ 6

1.3. Our interest in the CB[n] supramolecular chemistry............................... 6 1.4. The aim of this thesis ............................................................................. 7 1.5. General synthetic considerations ........................................................... 7

1.5.1. Mixed-chelate ruthenium complexes ......................................................... 7 2. The Ruthenium-Viologen System ................................................... 8

2.1. Introduction ............................................................................................ 8 2.1.1. The CB[7-8]-viologen system .................................................................... 9 2.1.2. Aim of this study ....................................................................................... 9 2.1.3. General synthetic procedures ..................................................................10 2.1.4. Characterization of the host-guest system ...............................................10

2.2. Laser flash transient absorption measurements .................................. 11 2.2.1. Transient absorption measurements of 1 .................................................12 2.2.2. Transient absorption measurements of 1CB[8] ......................................12 2.2.3. Transient absorption measurements of 1CB[7] ......................................13 2.2.4. Light-driven formation of a [3]-rotaxane ....................................................14 2.2.5. Conclusions .............................................................................................15

3. The Ruthenium-Phenol System .................................................... 16 3.1. Introduction .......................................................................................... 16

3.1.1. The aim of this study ................................................................................16 3.1.2. Synthetic considerations. .........................................................................17 3.1.3. Investigation of the guests with CB[8] ......................................................17 3.1.4. Conclusion ...............................................................................................19

4. The Ruthenium-DV2+

-V2+

System ................................................. 20 4.1. Introduction .......................................................................................... 20

4.1.1. Aim of this study ......................................................................................20 4.1.2. Synthetic procedures ...............................................................................21 4.1.3. Host-guest analysis .................................................................................22

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4.1.4. Molecular dyads 3 and 4 ..........................................................................24 4.1.5. Light driven formation of a [5]rotaxane .....................................................25 4.1.6. LFTA of triad 5 (unpublished works) ........................................................27 4.1.7. Conclusion ...............................................................................................28

5. The Ruthenium-Viologen-Napthol System ................................... 29 5.1. Introduction .......................................................................................... 29

5.1.1. The aim of this study ................................................................................29 5.1.2. Synthetic procedures ...............................................................................30 5.1.3. Interaction with cucurbit[7-8] and CD. ....................................................31 5.1.4. Photochemical investigation with the guest and CB[8] .............................33 5.1.5. Conclusions .............................................................................................35

6. The Ruthenium-Viologen-Ruthenium Rotaxane System

Encapsulating CB[7-8] ............................................................................. 36 6.1. Introduction .......................................................................................... 36

6.1.1. Aim of this study ......................................................................................36 6.1.2. Synthetic procedure and characterization of the host-guest interaction ....36 6.1.3. Non-aqueous photoinduced viologen radical formation ............................40 6.1.4. Conclusions .............................................................................................41

7. An Efficient Water Oxidation System Based on Supramolecular

Assembly of Molecular Catalyst and Cucurbit[7]uril. ............................... 42 7.1. Introduction .......................................................................................... 42

7.1.1. The aim of this study ................................................................................44 7.1.2. Design and synthetic procedures .............................................................44 7.1.3. Host-guest interaction ..............................................................................46 7.1.4. Catalytic water oxidation ..........................................................................46 7.1.5. Theoretical calculations ...........................................................................48 7.1.6. Conclusions .............................................................................................48

8. Concluding Remarks .................................................................... 49

Acknowledgements

Appendices

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1. Introduction

As our daily life becomes more complex, the needs on the chemical industry to

produce both smaller and more advanced active compounds are increasing.

Examples of such systems are smaller transistors, more energy efficient

monitors.

As these compounds become more advanced the complexity of the synthesis

also increases. This increases costs as well as time to manufacture the

compounds needed for a specific process. Here is where the advantage of

supramolecular systems can be implemented, where the relative simplicity of

forming complexes via non-covalent interactions instead of chemical bonds, is

utilized.

This can, for example, be used in multicomponent redox-active systems,

commonly used to mimic and understand biological processes as well as

forming molecular machines. Modifying these complex systems via self-

assembly to supramolecular systems is a simple way of altering the properties

of the systems.

While practical industrial use within this field is still in its infancy,

supramolecular chemistry offers possibilities to improve not only our life but

also our understanding on how the nature works.

1.1. Supramolecular chemistry

Jean-Marie Lehn classified supramolecular chemistry as “chemistry of

molecular assemblies and of the intermolecular bond”.1 The cucurbit[n]uril

(CB[n]) is a macrocyclic host, defined as a molecular receptor that is arranged

as a ring, where the guest (or substrate) bind in the interior of the host. By

classification the CB[n] is generally a cavitand or endoreceptor compared to

exoreceptors or clathrands where the guest binds to the exterior of the host.

When small substrate such as an alkali metal is said to be encapsulated inside

the host, a simple host-guest complexation is formed. However with larger and

more complex systems, the guests can be composed of mechanically

interlocked components. Of these there are 3 basic systems defined, see

Scheme 1.2-3

Rotaxanes are defined as “interlocked dumbbell architecture”.

This means that the macrocyclic host is bound on a rod shaped structure with

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two bulky groups covalently connected on each side preventing the separation

of the components. Catenanes are ring formations mechanically interlocked. In

either case the systems cannot be separated back to their components unless

chemical bonds are broken. Psuedorotaxanes on the other hand have no such

stoppers and the mechanical interaction is as such dependent on non-covalent

interactions, often a precursor to the rotaxanes and catenanes.

Scheme 1. Schematic representation of Psuedorotaxanes(left), rotaxanes (middle)

and catenane(right).

1.2. Cucurbit[n]uril

The name of the cucurbit[n]uril comes from the Latin word “cucurbitaceace”

which is the family name of the pumpkin plants. The CB[n] molecule has

received considerable attention and has been the focus of many different

reviews over the years.4 The molecule is cylinder formed and has a cavity

accessible from the exterior by two polar portals.

Figure 1. Picture of the electrostatic potential of the CB[7] left and molecular

structure right.

Similarly to cyclodextrin the interior is hydrophobic and can bind to

hydrocarbon substrates. Unlike the cyclodextrin, however, the host can bind to

protonated complexes due to the externally pointing carbonyls.

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As our work began, there was already a broad interest towards this field of

study. The research can be said to be broadly aimed towards three different

fields; (1) synthetic studies; (2) new inclusion complexes and the chemically

induced movement of a guest molecule; (3) the host being used to catalyse

chemical processes and reactions.

1.2.1. Synthetic studies

The CB[n] is self-assembled from the acid-catalyzed condensation reaction of

glycoluril and formaldehyde where the cucurbit[6]uril (CB[6]) host was the

first synthesized in 1905 by Behrend and coworkers.5 They were, however, not

able to fully understand the chemical structure, and it was referred to as

“Behrends polymer”. Full characterization was not reported until 1981 by

Mock and coworkers.6 The first study was host-guest interactions, where the

recognition behavior of CB[6] with and variety of guests were explored and

the tight binding with ammonium ions was found in water.7

Day and Kim continued to explore synthetic procedures in milder conditions

forming new homologues n=5, 7 and 8.8 Isaacs and coworkers has continued

the work towards understanding the formation of the CB[n], showing that the

pathway is based upon a step growth cyclopolymerisation.9

The research into improving the solubility or make other adjustment to the

supramolecular properties of the host have also received a significant

attention,4i, 10

with several classes of derivatives including functionalized,

inverted,11

and nor-seco-CB[n].12

Kim and coworkers have for example shown

how addition of reactive groups has been used to attach the host onto solid

surface,10

which can be important for practical industrial use.

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1.2.2. Inclusion complexes

The cavity of the CB[5-8] hosts varies from 4.4 to 8.8 Å in diameter and have,

compared to crown ethers (CE) and CD, a very rigid structure, see table 1. This

varying cavity and portal size is what gives the host its remarkable molecular

recognition properties.4k

Table 1. Cavity sizes of CB[5] to CB[8].

CB[5] CB[6] CB[7] CB[8]

Outer diameter a 13.1 14.4 16.0 17.5

Cavity (inner) b 4.4 5.8 7.3 8.8

Cavity (entrance) c 2.4 3.9 5.4 6.9

Height d 9.1 9.1 9.1 9.1

This difference in size has yielded a wide range of publications investigating

the properties of the homologues. CB[5] has a very small cavity and can

mainly bind at the cavity edge with substrates such as ammonia, lead and

alkali metal ions.13

The CB[6] compound with its slightly larger cavity has been extensively

explored to hold substrates such as diaminoalkanes and alkali group ions.14

Solvents like THF, benzene and xylene derivates have also been investigated,15

as well as thiols and dyes.16

It has also found to bind to transition metals17

as

well as lanthanides.18

CB[7] have a slightly larger cavity size compared to -CD, hence it can bind to

a much wider range of guests compared to the smaller CB[5-6]. These include

aromatic compounds such as imidazoles,19-20

stilleben,21

viologen and

analogues,22-26

and pyridinium27-28

among others.

CB[8] is similar in size to the -CD and can also hold a wide range of

positively charged compounds,4 as well as even larger guests such as cyclen

and cyclam.29

The host has even been found to work as exoreceptor to

fullrene,30

where two guests were bound to the portals. The CB[8]s large cavity

is even large enough to hold two substrates simultaneously.31-52

Even though

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CB[7] in rare cases can hold two guests,53

the larger cavity of CB[8] gives it

the ability to bind to a larger variety.

The two guests bound to CB[8] can be homo-guest pairs, as observed with

naphthalene derivatives,31

stilbene derivatives,32

cinnamic acids,43-44

coumarins,40

viologen derivatives,33-34

tetrathiafulvalenes36

and acridines.47

A

second option is hetero-guest pairs, usually comprising of an electron poor

guest, such as viologen and an electron rich guest such as naphthalene,

dihydroxybenzene or similar. 48-52

The different amounts of units in the host and thus size give considerable

difference in its affinities for the guests, see Figure 2.

Figure 2. Examples of host guest interactions of CB[6-8].

1.2.3. Molecular machines

Molecular machines have been defined as “an assembly of discrete

components designed to perform mechanical-like movements (output) as a

consequence of appropriate external stimuli (input)”.54

The earliest example

containing CB[n] was published by Mock and coworker in the early 1990,55

where a CB[6] was shuttled along a triamine string by changing the pH value.

Several other groups have continued exploring this amine CB[6-7] system

using different stimuli such as UV/Vis and fluorescence. Kaifer and coworker

have been exploring the ferrocence- or acid-linked viologen with CB[7] as

host, utilizing the electrochemical reduction or pH as stimuli to control the

movement of the host.56-57

The charge-transfer interactions have been used to control intermolecular

folding processes, and have been used to create different types of shuttles.58-59

Dendrimer-type structures bound to viologen and phenols have also been

found to form charge-transfer type complexes, and the substrates could shift

controlled by electrochemical stimuli.60

Other examples include formation of

hydrogel or displacing guests via the addition of salt.61-62

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1.2.4. Catalysis of reactions and other improvements

Mock and coworkers were once more the first to recognize the ability of CB[6]

to catalyze a chemical reaction.63

They could increase the rates of 1,3

cycloadditions between alkynes and alkyl halides by a factor of 5.5x104.63

CB[7-8] have been employed to catalyze different types of photocycloaddition

reactions as well as being able to hydrolyze amides.64-71

Isaacs and coworkers

recently reported biological catalysis, utilizing CB[7] to regulate an inhibitor

with DNA.72

1.2.5. Drug delivery

Considerable interest has also been devoted to the use of the host for drug

delivery.73

The drugs investigated with the host are within a broad field.

Examples include medicines used against cancer, leukemia and even for the

stomach. The effect of the host are among others the ability to improve

solubility,73f

reduce toxicity,73b

improve stability or even activate a drug.73e

Recently Nau and coworkers published an in vitro study of CB showing a very

low toxicity.74

1.3. Our interest in the CB[n] supramolecular chemistry

We became interested in the cucurbit[n]uril compounds in early 2005 in our

group due to its unique properties. Its ability to stabilize viologen radical

dimers led to the investigation of CB[n]‟s effect on the electron transfer

mechanisms (paper I and II). As previously presented, the polar cavity edges

can readily form hydrogen-bonds to substrates as well as clathrands (externally

bound guests).

As the main focus of our group is on alternate energy sources, the

understanding of the Oxygen evolving complex (OEC) that exist in the PS II

system is of great importance. This complex system is still one of the mysteries

of nature, and the foundation that gives plants and other photosynthetic

organisms the ability to convert sunlight to chemical energy. The ability to

design systems via self-assembly is a very good way of altering and studying

the PSII system, and more specifically Water Oxidation Catalysts (WOCs).

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1.4. The aim of this thesis

The aim of this thesis is to develop new tools and methods in supramolecular

chemistry with cucurbit[n]uril, and more specifically explore the bindings of

the CB[n] host in systems with photosensitizer bound redox active

components.

1.5. General synthetic considerations

1.5.1. Mixed-chelate ruthenium complexes

The synthetic approach to preparing the ruthenium complexes is shown in

figure 3. For the complexes in this publication two precursors were prepared,

Ru(DMSO)4Cl275

and cis-Ru(bpy)2Cl2,76

in either case the complex RuCl3∙H2O

were used as starting material. The advantage of DMSO ligands are that they

are easily displaced, allowing milder conditions compared to the starting

material.

Figure 3. Synthetic approach to the preparation of mixed-chelate ruthenium

complexes.

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2.

The Ruthenium-Viologen System

(Paper I-II)

2.1. Introduction

To study the photosystem II (PSII) model system and the electron transfer (ET)

mechanisms, where ruthenium polypyridine complexes connected to an

acceptor are commonly used. Bispyridinium ions are some of the most popular,

reversible electron acceptors, where methylviologen (N,N-dimethyl-4,4-

bipyridinium, MV2+

) is most often used.77

Figure 4. The structure of methylviologen (above) and complex 1 (below) used to

explore the long-lived charged separate state.

An earlier study by Mallouk and coworkers investigated photoinduced

intramolecular ET reactions of ruthenium trisbipyridyl-viologen molecules

[(2,2-bipyridine)2Ru(4-CH3-2,2-bipyridine-4)(CH2)n(4,4-bipyridinium-

CH3)4+

] (n=1-8). The lifetime of the photo induced charge separated state was

explored yielding slight changes in the lifetime due to the difference in chain

length.78

Scheme 2. The pathway of the photoinduced charge-separated state.

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The pathway is light driven formation of the Metal to Ligand Charge Transfer

(MLCT) state of the complex followed by an intra or intermolecular electron

transfer to the acceptor, see scheme 2. This unstable system then reverts via

charge recombination to the ground state. β-CD has been used to encapsulate

the spacer chain in order to control the transient state decay rates.78

As MV2+

was known to be completely encapsulated by the CB[7-8] host,25-26,33

the

investigation of its effect on ET mechanism was a natural starting point.

2.1.1. The CB[7-8]-viologen system

In 2002 Kaifer and Kim and coworkers presented the interaction of viologen

with the hosts CB[7] and CB[8] as previously mentioned.25-26,33

In the case of

CB[8], it was found that the substrate could strongly bind inside the cavity

with a Ka= 1.1 x 105. When reduced to its radical form, the MV

+∙ can either

form monomer radical or complex into its dimer radical form. The CB[8]s

voluminous cavity is however large enough to accommodate two

methylviologen and was found to enhance this dimerization process by a factor

of 105, see scheme 3.

CB[7] on the other hand is not large enough to form

dimer radical form and was instead found to hinder the formation of radical

dimer. It was concluded that quantitative control of the addition of host

allowed control of the stoichiometry of the host-guest complex.

Scheme 3. Formation of the viologen radical dimer inside the CB[8] cavity.

2.1.2. Aim of this study

The goal of this study was to explore how the cucurbit[n]uril host would affect

the photoinduced charge-separate state of the Ru-MV system. A second goal

was to investigate the possibility of forming a [3]-rotaxane between two guests

and CB[8].

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2.1.3. General synthetic procedures

Triad 1 was synthesized following the known route as depicted in scheme 4.78

Commercially available 4,4‟-bipyridine was methylated with iodomethane,

affording b after ion exchange to PF6- counterions.

78 4,4‟-dimethyl-

2,2‟bipyridine was reacted with freshly prepared LDA (lithium

diisopropylamine) under nitrogen at -78 0C for 1 h, addition of 1,3-

dibromopropane and purification gave precursor d. Stirring precursor d in

DMF with methylated 4,4′-bipyridine (b) and subsequent purification gave the

bi-dentate ligand e. Coordination with cis-Ru(bpy)2Cl2∙2H2O gave the target

complex 1. In general the cationic complexes described in this thesis were

purified by column chromatography on silica gel with a mixture of

H2O/CH3CN/KNO3 as eluent.

Scheme 4. Synthetic route for complex 1

2.1.4. Characterization of the host-guest system

In order to understand the effect of the host, careful investigation of the

inclusion complexes of 1 and either of the hosts CB[8] and CB[7] was

performed, see scheme 5. It was found that the CB[8] host present itself

squarely on the viologen, while the CB[7] has a more dynamic position. The

latter host could be detected both partly on the inner part of the viologen and

on the carbon linker, see scheme 5 (top figure). This difference in binding

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modes is well established and CB[7]s preference to the linker has been

thoroughly investigated by other groups.79

Scheme 5. Schematic illustration for the 1:1 inclusion complexes of 1 with CB[7] and CB[8].

Confirmation of the inclusion was done by HRMS and UV/Vis titration

confirming the 1:1 binding mode. The stability of the complexes was found to

be very high, with a binding constant of 1.2×105 M

-1 for 1 and CB[7] and

3×105 M

-1 for 1 and CB[8]. These types of strong interactions are consistent

with the above mentioned different binding modes.

2.2. Laser flash transient absorption measurements

To investigate the effect of the CB host on photoinduced ET and charge

recombination, laser flash transient absorption (LFTA) measurements are

commonly used.80

The 1:1 inclusion complexes as well as the well-known

complex 1 were irradiated in water solution. Laser Irradiation was done

utilizing an 8ns laser pulse at 532nm. The absorption spectrum is then

followed on the nanosecond timescale. Any bleaching or negative peaks would

indicate that compound is disappearing from the system, such as changing

oxidation state. Any positive peaks conversely indicate that something is

formed.

The changes of the MV2+

moiety can be observed via bleaching at 253 nm (the

absorption band of the viologen) and peak formations at 400 and 600nm, due

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to the MV2+

→MV+∙

process. Ru2+

(bpy)3, as a photosensitizer, is well

investigated and have both an intense ligand-centered absorption band at 301

nm and a d→* MLCT absorption band at 450 nm.80, 81

The excited state

ruthenium moiety can then be indicated by an absorption from the reduced

bpy∙- ligand in the

3MLCT state at a maximum of 370 nm, and a bleaching at

450 nm.

2.2.1. Transient absorption measurements of 1

Complex 1 alone yielded a transient absorption spectrum dominated by a

bleaching band around 450 nm, as well as a positive absorption band around

370 nm. No clear signals for the formation of the MV+•

radical (at 600 nm or

400 nm) could be observed due to the short lifetime, as seen in figure 5. For

complex 1, the Ruthenium recovery is due to charge recombination was

observed from the 450 nm bleaching and is fitted well with a single-

exponential decay curve with a time constant of 10 ns.78

300 400 500 600 700-10

-5

0

5

10

15

A

/nm

Figure 5. Time-resolved absorption spectra for complex 1 in aqueous solution at

room temperature, the data were recorded at delays of 15 ns, 32 ns, 49 ns, 66 ns, 83 ns, 100 ns following excitation of 532 nm laser pulse.

2.2.2. Transient absorption measurements of 1CB[8]

Figure 6 shows the nanosecond transient absorption spectra of the 1CB[8]

system at different time domains after laser flash. The spectra is dominated by

a bleaching band around 450 nm, together with a positive absorption around

370 nm and also a emission band at 650 nm indicating the excitation of the

sensitizer, as well as a absorption peak at ca 400 nm from the MV+•

radical.

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-2

0

2

4

300 400 500 600 700

A

/nm Figure 6. Transient absorption spectra of complex 1 in the presence of 1 equiv. of CB[8] in aqueous solution at room temperature, data recorded at delays of 170 ns,

335 ns, 500 ns, 665 ns and 830 ns following the excitation of 532 nm laser pulse.

With the CB[8] host the decay curve at 400nm fitted well to a double

exponential process with time constants of 2060 ns (99.85%) and 30 ns

(0.15%), see figure 6. The recovery kinetic at 450 nm could be fitted with a

double-exponential decay by time constants of 424 ns (88%) and 12 ns (12%).

It was found as the host-interacted systems where measured, double

exponential processes were observed. The faster recovery (12 ns) agreed well

to the measurements made before host inclusion, which indicate that the

smaller component most likely was due to dissociation of the 1:1 inclusion

complex. This also showed that the bleaching at 450 nm and subsequently the

formation of the Ru2+

-(bpy)3 ground state was faster compared to the lifetime

of the viologen moiety.

2.2.3. Transient absorption measurements of 1CB[7]

300 400 500 600 700

-10

-5

0

5

10

15

A

/nm

Complex 1 + CB[7]

Figure 7 Time-resolved absorption spectra for 1:1 inclusion complex of 1+CB[7] in

water solution at room temperature, data recorded at delays of 17 ns(■), 34 ns(●), 51 ns(▲), 68 ns(♦), 100 ns(▼) following the laser excitation at 532 nm

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The time resolved spectra for the 1:1 binding mode of 1-CB[7] is displayed in

figure 7. In this case, however, with CB[7] host, no clear signals for the

formation of the MV+•

radical (at 450nm or 600 nm) could be observed as had

been the case in the presence of CB[8]. This result can most likely be

explained by the different binding modes of CB[7] and CB[8] with the MV2+

as previously shown. This indicates that the complete encapsulation is vital for

the long-lived charge separate state.

For this system as in dyad 1 alone, the decay of the bleaching at 450 nm was

instead investigated. The recovery of Ru2+

for 1-CB[7] could, as in the case of

1-CB[8], be fitted with to bi-exponential process with two time constants (11

ns (24%) and 280 ns (76%)). The faster recovery rate constant agreed with the

value for the molecular dyad 1 alone (24%). The main component (76%)

represents the relatively slow charge recombination of Ru3+

-MV+•

due to the

inclusion of 1 into the cavity of CB[7].

This shows that the charge separated state Ru3+

-MV+•

generated after

photoinduced ET can be stabilized to some extent by the binding of the

viologen radical to CB[7]. However when compared to the CB[8] system,

CB[7] is considerably less efficient in stabilizing the charge separated state.

2.2.4. Light-driven formation of a [3]-rotaxane

To investigate the possibility of forming a [3]-rotaxane, and to utilize the high

binding constant of the viologen radical dimer inside the CB[8] cavity, an

external sacrificial electron donor was added. Triethanolamine (TEOA) is a

common and well known sacrificial electron donor,82

and can stabilize the

system and the formed MV+•

radical by reducing the photo-oxidized sensitizer.

The irradiated solution of 1 with CB[8] was investigated with UV/Vis and 1H-

NMR. Slight shifts could be observed from the viologen protons as well as a

broadening of the peaks indicating a paramagnetic complex. The color change

that of the solution indicates that TEOA does sufficiently slow down charge

recombination between Ru3+

and MV+•

so that the viologen radicals can

undergo dimerization, forming a stable dimer leaving the excess CB[8] in

solution.

UV/Vis showed the typical peaks of the radical dimer in the spectral changes.

After addition of 1 equiv. CB[8], two absorption peaks at 370 nm and 540 nm

were observed33,83

The peak intensity increased as the irradiation time

prolonged, and confirmed the radical dimer formation (see figure 8). 1 alone,

when irradiated, gave only the viologen monomeric radical peaks on the

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UV/Vis while the proton peaks completely shifted outside the normal NMR

window confirming the rotaxane formation.

Figure 8. Absorption spectra of 1 (4.0×10-5 M) and TEOA (5×10-2 M) in the absence

of CB[8] (left), and in the presence of 1 equiv. CB[8] (4.0×10-5 M) (right), (a) before

and (b) after 5 min, (c) after 20 min light irradiation. Inset: (d) after 20 min light irradiation, (e) after exposing the cuvette to air (oxygen), the spectral curve returns to the original one.

2.2.5. Conclusions

The binding modes between CB[7] and CB[8] differed, as evidenced by 1HNMR, ESI-MS, and UV/Vis measurements. Due to these different modes of

encapsulation the intramolecular ET gave rise to vastly different long-lived

charged separate states.

In the presence of the sacrificial electron donor, the photoinduced long-lived

charge separated state of molecular dyad 1 with CB[8] gave a very stable

Ru2+

−MV+•

radical, which could be used to create a light driven molecular

“lock”.

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3.

The Ruthenium-Phenol System

(Paper III)

3.1. Introduction

A phenol analogue has been used in conjunction with viologen and CB[8]

previously. 60

It was shown that the system worked well when the guests are

connected to dendrimer type systems, wherein the formed charge transfer

system can be bound together followed by the viologen radical dimer system

see figure 9. Theoretical calculations showed that the cavity of CB[8] indeed

was big enough to hold more than two viologens. In the former cases, the

systems were designed so that only two substrates could be included in the

system. The question we asked was: what would happen if the system was

designed so that a trimer is possible?

Figure 9. A charge transfer systems based upon dialkoxybenzene and viologen.60

3.1.1. The aim of this study

The aim of this study was to investigate the phenol-viologen system when

linked to a photosensitizer and study the radical dimer formation process.

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3.1.2. Synthetic considerations.

The dyad 2 was synthesized following earlier published route as depicted in

scheme 6.110

The commercially available 4,4‟-dimethyl-2,‟bipyridine was

reacted with freshly prepared LDA (lithium diisopropylamine) followed by

addition of 4-(chloromethyl)phenyl acetate yielding bi-dentate ligand h.110

Coordination with cis-Ru(bpy)2Cl2∙2 H2O gave the target complex 2.

Scheme 6. Synthetic route for 2.

3.1.3. Investigation of the guests with CB[8]

No interaction between complex 2 and CB[8] was observed on 1H NMR

experiments. This was due to destabilization of the polar hydroxyl group with

the polar cavity edges of the CB[8] host. As one equivalent of MV2+

was added

into the solution CB[8] and 2, all protons of the ethyl chain and the phenol ring

in 2 underwent an up-field shift indicating an interaction with the cavity of the

host. The protons of the MV2+

moiety underwent a similar up-field shift

indicating an interaction with the cavity of the host, as well confirmed by

HRMS.

The stoichiometry for the binding of 2, MV2+

and CB[8] was established by

UV-Vis absorption titration measurements, giving a 1 : 1 : 1 binding model

with an association constant of 3.8 × 105 M

−1

The complex 2 has three reduction peaks attributed to the reductions of the

three bipyridine ligands, and one oxidation peak at 0.896 V attributed to the

oxidation of Ru(II), which are similar to the ruthenium(II) tris-bipyridine

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complex.84

Electrochemical investigation showed that the oxidation potential of

phenol is 1.208 V from DPV. As the oxidation potentials of Ru(II) is at 0.896 V

vs. Ag/Ag+ which is a clear indication that Ru(III) cannot oxidize the phenol.

The photoinduced ET processes in this system were studied via NMR and

UV/Vis. The 1: 1: 1 host–guest reaction process was monitored by 1H NMR.

No spectral changes were observed, even after several hours of light

irradiation, with no free 2 being observed by 1H NMR. To obtain additional

information three systems were investigated; (1)the documented Ru(bpy)3 +

MV2+

+ CB[8]; (2) the 1:1:1 system as described above with different amounts

of CB[8] and (3) the 2 + MV2+

system see figure 10.

Figure 10. 1H NMR of the three systems a), b), and c) after addition of 10 equiv. of

TEOA and irradiated for 15 min.

It could be concluded that the phenol moiety of 2 indeed still interacts

dynamically with the CB host dynamically, due to the fact that no free 2 could

be detected.

UV-Vis spectra were measured to understand the ET process. It was found that

that a shift in the peaks could be observed. System b gave peaks at 368, 546

and 853 nm. In the case of system a these peaks occurred at 367, 540 and 880

nm. The ca 30 nm shift was consistent and repeatable, and clearly showed that

a third moiety as the phenol in this case, was interfering slightly with the

geometry of the MV radical dimer pair inside the host.85

This behavior can be

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explained in the following fashion. The energy levels of the two interacting

radicals inside the host are due to the electron rich phenol are merged into a

higher ground state and a lower excited state level. The difference between

these two energy levels and therefore the CT excitation energy becomes higher,

see scheme 7.

Scheme 7. A proposed structure for the formation of the stable 2–(MV+∙)2–CB[8] partner radical trimer after photoinduced ET.

3.1.4. Conclusion

In conclusion, accompanied by the positively charged MV2+

, the phenol moiety

of guest molecule 2 can be inserted into the cavity of CB[8], forming a stable

1:1:1 inclusion complex 2-MV2+

-CB[8]. This is an interaction that agrees with

previous published interactions as described above.60

However, when

irradiated in the presence of sacrificial electron donor, a stable 2-(MV+•

)2-

CB[8] partner radical dimer in the CB[8] cavity can be generated with light

and the structure for this radical dimer has been proposed. Molecular oxygen

can quench the radical dimer and regenerate the original 1:1:1 inclusion

complex. These results may indicate a new type of interactions and can

hopefully provide some fundamentals to new types of designs of molecular

devices.

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4.

The Ruthenium-DV2+

-V2+

System

(Paper IV-V)

4.1. Introduction

During the past years, several groups have reported the dynamic interactions of

a CB[n] host to different positions of a guest using either CDs, proton or

electron transfer reactions.86

These had been performed on mainly systems

such as donor-acceptor complexes, ferrocence-acceptor or by proton transfer

from amide based polymers.

Continuing our earlier work with the Ru(bpy)3-MV2+

and CB[7,8], we decided

to expand this area by introducing a secondary viologen derivate to the system

with CB[8]. Dimethyl methylviologen (N,N-dimethyl-3,3‟-dimethyl-4,4‟-

bipyridinium, (DMV2+

) also function as an electron acceptor, but is more

difficult to reduce compared to the parent viologen.87

The properties of DMV and MV when linked have been investigated

previously.88-89

Crown ether was introduced and the changes in the long lived

charged-separate state was investigated.88

The authors concluded that the

crown ether decreased the reorganization energy which according to classic

Marcus theory would increase the lifetime of the charge separate state.

Stoddart and coworkers also designed a molecular “abacus”89

in which crown

ether could shift to the viologen unit when reduced to its radical form.

4.1.1. Aim of this study

The goal of this study was to explore a new guest molecule as well as to

explore if the host could shift position with two different electron acceptors.

Also the photochemical [5]-rotaxane is explored (see scheme 8).

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Scheme 8. The chemical structures of compounds MV2+, DMV2+, 3, 4 and 5.

4.1.2. Synthetic procedures

The dyad 3, 4 and triad 5 was synthesized following the route as depicted in

scheme 10. N,N-dimethyl-4,4‟-bipyridinium was synthesized according to a

procedure of Rebek and coworker.90

A two-step process with sodium based

reductive dimerization utilizing TMSCl, followed by oxidation with KMnO4.

The dyads 3 and 4 were synthesized stepwise where crude purification of the

precursor I, j was performed via precipitation and ion exchange. The synthesis

of triad 5 was performed from a modified procedure of an analogue 88

as seen

below (scheme 9, 10).

Scheme 9. Synthetic route for DMV2+ and precursor i, j

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Scheme 10. Synthetic route for dyad 3, 4 and triad 5

4.1.3. Host-guest analysis

The inclusion complex between the guest DMV2+

and CB[8] can be observed

on 1H NMR spectral changes, and is consistent with similar systems.

33, 86 The

inclusion was as well confirmed via HRMS and UV/Vis titration. A binding

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constant of (2.6±0.3) × 105 L mol

1 was obtained, indicating a preference of the

CB[8] on the DMV2+

moiety compared to the MV2+

moiety.33

This difference in binding constants was observed by dissolving equivalent

amounts MV2+

, DMV2+

in water. The CB[8] host was incrementally added and

a strong preference was found for the DMV2+

-CB[8] interaction. At the 1:1:1

(MV2+

:DMV2+

: CB[8]) system, a broadening of the MV2+

signals was

observed, suggesting a weak dynamic interaction.

The reduction potential of DMV2+

was found to be 400 mV lower compared to

the MV2+

in aqueous solution, indicating that a selective reduction was

possible. When included in a CB[8] host in the presence of 0.5 and 1

equivalents of CB[8] a slight negative shift of a total of 15 mV was detected,

indicating a similar effect as in the MV2+

-CB[7] system.25-26

Spectroelectrochemistry was performed to further analyse the host-guest

interaction see figure 11. The radical cation was clearly observed at 390 and

790 nm87-89

in both aqueous and acetonitrile solution. When performed in

aqueous solution a third peak at 315 nm was detected.

The exact origin of this last peak could not be determined, but can be derived

from either the doubly reduced specie DMV0 or possibly the DMV

+∙ radical

pair. With 1 equivalent of CB[8] added to the solution of DMV2+

the intensity

of the peak at 315 was strongly reduced while the peaks at 390 and 790 nm

were essentially unaffected.

Figure 11. UV/Vis spectroelectrochemistry of DMV

2+ at 5 mM concentration (solid

line), with 1 equiv. CB[8] (dashed line) and baseline (dotted) at 1.1 V vs. Ag/AgCl.

Even though the measurements were conducted at several concentrations of

DMV2+

and amounts of CB[8] no new spectral peaks were found, leading to

the conclusion that the DMV+∙

cannot form a radical dimer inside the CB[8]

host. The same conclusion has been reached with other larger derivate of the

viologen like DQ2+

, DAP2+

and DPT2+

(shown in scheme 10).91

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4.1.4. Molecular dyads 3 and 4

After the interactions of the DMV2+

substrate had been determined, the dyads

followed the same investigation procedure with NMR, HRMS,

electrochemistry and spectroelectrochemistry as mentioned above.

1H NMR analysis indicated a steric hindrance when two equivalents CB[8] was

added to dyad 3. This was not observed on the second dyad (4) where a six

carbon chain was separating the two viologens. Similar dynamics have been

observed on other [2]-psuedorotaxane with dual CB hosts. 75

The linkage as well gave electrostatic interactions between the viologen

moieties, lowering the potential of the MV2+

→MV+·

by up to 100mV. When

CB[8] was added to the system, by one half equivalents a small shift towards

the positive region could be detected on the first reduction wave. This effect

was more strongly seen on the oxidation peak but also the reduction peak

shifted. The electrochemistry was performed at different speeds giving

different shifts of the reduction peak, all in all indicating a chemical process.

However the shift of the V2+

→V+∙

was less pronounced compared to the MV2+

-CB[8] system.33

Confirmation was obtained via spectroelectrochemistry

where the systems was investigated with and without host (see figure 12).

Figure 12. UV/Vis spectro-electrochemistry of 3 (left) and 4 (right) in water solution,

potential applied at 0.56 and 0.66 V vs. SCE respectively. Compound only

(dashed line) and with 0.5 equivalents CB[8] (solid line) and before potential was applied (base line).

The dyads were reduced at a potential of 0.56V vs. SCE, selected so that only

the MV2+

moiety could be reduced. In the absence of CB[8] only the MV+·

radical was detected in both cases with the characteristic peaks at 397 and 600

nm on UV/Vis.

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As one half equivalent of CB[8] were added to the solution peaks at 397 nm or

600 nm were not observed. Instead very strong peaks at 370, 550 and 880 nm

were observed in the UV/Vis spectrum, attributed to the formation of MV+·

radical dimers inside the cavity of the CB[8] (Figure 12, top).33

Stability

measurements were performed by repeating the tests and showed that the

systems were stable.

4.1.5. Light driven formation of a [5]rotaxane

To form rotaxane in a similar way as we previously performed92-93

for 1, the

dyad 3 was covalently linked to a Ru(bpy)3 unit, working both as a stopper and

sensitizer, see scheme 10. When the CB[8] host was included into the system

and investigated via 1H NMR it was found that triad 5 behaved slightly

differently compared to dyad 3. As the second host was introduced the peaks

from the MV2+

moiety shifted and became sharp, indicating strong interaction

compared to the weak interaction discussed above.

Investigation showed that in this instance the CB[8] moved slightly away from

the DMV moiety instead, “making room” for full inclusion of the second host

on the MV moiety. And indeed reported data support this where it has been

found that the CB host shows an increased ability to move away from the

center of an alkylated viologen compared to methylviologen, as previously

discussed.79

Electrochemistry measurements indicated a very complex system but do show

the classic indication of the dimer formation when one half or more

equivalents CB[8] are added to the system. The light driven investigations for

the complex alone showed as expected only the peaks of the free

Ru2+

―DMV2+

―MV+•

monomeric radical, (see Fig. 10b). As two equivalents

of CB[8] to the solution of 5 and TEOA, only a very strong peak at 370 nm and

a broad peak around 540 nm and a broad peak at 870 nm were observed. These

peaks are attributed to the formation of MV+·

radical dimers inside the cavity

of the CB[8], as in the case of the dyads 3 and 4 above.

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Figure 13. UV/Vis spectra of 5 (4 × 10-5) in water solution, with TEOA as sacrificial electron donor. a) before irradiation (solid); (b) after 50 min light irradiation (dashed); c) with 2 equiv. CB[8] before irradiation (dotted); d) after 50 min light irradiation with 2.0 equivalents CB[8] (dotted- dashed).

NMR investigations as well showed that even when irradiated, the DMV units

were still found to be inside a CB[8] host, confirming that the [5]-rotaxane can

be formed as shown in scheme 11.

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Scheme 11: schematic representation of the light driven interaction between 5 and

CB[8], forming the [5]-rotaxane.

§

4.1.6. LFTA of triad 5 (unpublished works)

Triad 5 was investigated via laser flash transient absorption with the CB host,

as discussed in 2.3. The MV+∙

could not be detected at 600 nm, instead for

comparison the decay of the *Ru

2+ (bpy)3 ground-state bleaching at 450 nm

was used. Without any host included, the lifetime of the charge separated

system was 20.3 ± 2.1 ns, which is similar to earlier reported analouges.88

When one equivalent CB[8] was positioned on the DV2+

moiety, the lifetime

was increased to 303 ± 30 ns while when two equivalents of CB[8] were used

a lifetime of 378 ns ± 10 ns was observed. Inclusion into one equivalent CB[7]

has also been investigated yielding a lifetime of 397 ns ± 2 ns.

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4.1.7. Conclusion

The DMV-MV system does work with the CB[8] host. Since the DMV as a

substrate cannot form a radical dimer inside the host, selective movement of

the CB[8], can be performed to the Ru2+

―DV2+

―V+•

monomeric radical,

forming a V+•

radical dimer. Further TA investigations are ongoing, as shown

in the unpublished material section, and indicate that the host greatly stabilizes

the long lived charge-separate state.

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5.

The Ruthenium-Viologen-Napthol System

(Paper VI-VII)

5.1. Introduction

Charge transfer complexes have been used to create molecular machines and

other systems with the CB[8] due to its ability to form a high strength

encapsulation that easily can be broken due to the hosts strong interaction with

the radical dimer. Kim et al made the first system in 200149

and several

systems have since been investigated (scheme 12).58-59

Scheme 12. Example of an earlier published molecular loop, utilizing the charge-transfer system of napthol-viologen vs. the viologen radical dimer-pair.58

5.1.1. The aim of this study

The goal of this study was to explore the dual host-interaction on a guest

complex as well as to explore the stability of the charge-transfer complex when

covalently bound to a photo sensitizer.

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Scheme 13. The structures of Ru2+-MV2+-DHN (triad 6), β-CD and CB[7-8]

5.1.2. Synthetic procedures

The triad 6 was synthesized following the synthetic route as depicted in

scheme 14. A solution of 6-methoxy-naphthalen-2-ol and 1, 6-dibromo-hexane

was stirred in acetonitrile in the presence of K2CO3 was stirred for 24 h at 80

ºC to form precursor m, Several solvent, temperature and bases were tested and

these reaction conditions gave sufficiently good solubility of the base for

optimal yields. Following reaction of m with viologen gave n. The ligand o

was formed by reacting precursor n with d in DMF. The triad 6 was formed by

coordinating the bi-dentate ligand o with cis-Ru(bpy)Cl2•2H2O

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Scheme 14. Synthetic route to triad 6

5.1.3. Interaction with cucurbit[7-8] and CD.

To study the inclusion complex formation of the triad 6 with β-CD and CB[7],

different equivalents β-CD and CB[7] were added to the solution of triad 6, see

scheme 15. After preliminary addition of either host the free positions could be

determined via 1H NMR, indicating that the CB[7] host binds to the viologen

moiety in the complex, see scheme 15,a.

Similar tests upon addition of β-CD, also showed a 1:1 inclusion complex, as

well as revealed that the intermolecular host exchange rate between the free

guest and the β-CD-bound guest is fast on the NMR time scale. The 1H NMR

demonstrated that the β-CD in the 1:1 inclusion complex is positioned on the

naphthalene unit, see 15, b.

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The addition of β-CD into a 1:1 inclusion complex of 6 and CB[7] revealed the

the CB[7] had moved further towards the ruthenium moiety while the β-CD

was mainly positioned at the six carbon chain (15,c). The shift of the CB[7]

was even more pronounced than detected in the 1:1 system of 1-CB[7]. Even

the 2, 2′-bipyridinium ring were partly inside the cavity of the CB[7]. Addition

of CB[7] to the 1:1 inclusion complex of 6 and β-CD yielded the same final

product, showing the two possible pathways, as shown in scheme 15.

These observations indicated that β-CD can be displaced by CB[7] from the

1:1 inclusion complex of 6 + β-CD, forming the 1:1 transit-complex of triad 6-

CB[7]. We conjecture that both hosts moving closer to “stopper” is due to the

shielding effect of the CB[7] on the MV2+

positive charges when partly

included in the cavity. This lessens the cationic influence on the β-CD, which

then can shift position to the six-carbon chain, tightening the „„nut‟‟ on the

„„bolt‟‟. In addition, the positive charges of Ru(II) might also have some

influence on this process. This phenomena is in agreement with earlier

observations from Liu and co-workers with the -CD and CB[7].86

Scheme 15. Schematic illustration of the interaction of A: 6 with CB[7] (1:1 equiv.); B: 6 with β-CD (1:1 equiv.); C: changes of interaction by addition of equivalent β-CD into a 1:1 inclusion complex of 6 and CB[7]; D: formation of the 1:1:1 ternary

inclusion complex by addition of equivalent CB[7] into a 1:1 inclusion complex of 6 and β-CD.

The 6CB[8] system with β-CD was also investigated. The well-known CT

complex was formed,49

where the 2,6-dihydroxynaphthalene moiety of 6 folds

back with viologen moiety inside the cavity of CB[8]. This interaction could

also be readily detected via UV/Vis where the complex show a distinctive peak

(λmax =566 nm) as discovered by Kim and co-workers (figure 14).49

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400 500 600 700 8000,00

0,02

0,04

0,06

0,08

0,10

0,12

0,14

0,16

0,18A

bs

Wavelength (nm)

400 500 600 700 800

0,0

0,1

500 600 700 800

0,00

0,01

0,02

Abs

Wavelength (nm)

Figure 14. Absorption spectra of ligand (left) and triad 6 (right) in the absence (solid

line) and in the presence of 1.0 equiv. (dashed line) of CB[8], inset showing the enlarged CT-band area.

The experiments were controlled by addition of β-CD host to the substrate 6

forming the above mentioned 1:1 host-guest complex, however when CB[8]

was added the complex yet again formed the charge-transfer complex and no

interaction could be detected between the complex and the β-CD.

Stoichiometry measurements of triad 6 with CB[8] by UV-Vis absorption

titration measurements verified this interaction. The data fitted to a 1:1 binding

model with a binding constant of 2.62×105 L mol

1. This value is very close to

the binding constant (3×105 L mol

1) of the molecular dyad where Ru(bpy)3 is

covalently linked to MV2+

by a four carbon chain as previously presented.92-93

5.1.4. Photochemical investigation with the guest and CB[8]

To study the possible photoinduced electron transfer processes in a system

containing the triad 6 without the presence of CB[8], an external sacrificial

electron donor, TEOA, was added to the solution of 6 as previously described. 1H NMR spectral changes clearly supported the formation of the Ru

2+- MV

+•

radical in triad 6. The broadened 1H NMR peaks are due to the paramagnetic

effect of the MV+•

radical. The measurements were repeated with addition of

CB[8]. Again, when the NMR tube was degassed with argon and irradiated for

3 h with light, the color of the solution changed from brown to dark green. 1H

NMR showed no proton shift in the NMR spectra before or after irradiation.

In contrast, the formation of V+•

radical dimer inside CB[8] has been observed

for a similar system as mentioned in the introduction. We concluded that the

steric factors designed into the system can withhold the formation of a radical

dimer, even with external viologen added to the solution.

The light-induced formation of the stable Ru2+

-MV+•

monomeric radical was

further confirmed by UV/Vis absorption. The two absorption peaks at 399 and

605 nm were readily observed while prolonged irradiation gave no further

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peaks. These two peaks are well known and due to formation of the monomeric

radical.25-26

The CB[8] induced CT complex gave rise to the two absorption peaks at 401

and 607 nm. The small redshift can be attributed to the electron rich DHN moiety

affecting the viologen. When comparing the spectrums, no other significant effect

on the spectrum could be found, see scheme 16.

Scheme 16. The formation of MV+• radical in 1:1 inclusion complex of 6 + CB[8] after photoinduced intramolecular electron transfer.

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5.1.5. Conclusions

The Molecular triad 6 can form a stable 1:1 inclusion complex with CB[7] and

β-CD. Two self-sorting system are found, where the β-CD either can be

released from the DHN moiety by the addition of CB[8] or shifted in position

in the case of CB[7]. Light irradiation in the presence of CB[8] only yields the

monomeric MV+•

. The formation and behaviors of the 1:1 inclusion complex

of the photoactive molecular triad 6 with CB[8] can provide basic

understanding for the future design of more advanced systems.

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6.

The Ruthenium-Viologen-Ruthenium Rotaxane System Encapsulating CB[7-8]

(Paper VIII)

6.1. Introduction

In contrast to cyclodextrin, the solubility of the CB[n] hosts is low. Especially

the CB[8] has a very low solubility even in aqueous solutions unless it

encapsulates a guest molecule. While few literatures have reported on the

inclusion of CB[7] in organic media,94

however none has been presented with

CB[8]. Work has instead been focused on modifying the CB host itself.11

6.1.1. Aim of this study

The goal of this study was to explore the possibility of moving the

cucurbit[8]uril complex into a purely non aqueous solution to investigate if the

host still was able to promote the dimer formation.

6.1.2. Synthetic procedure and characterization of the host-guest interaction

A dual ruthenium complex was designed with a central viologen moiety, upon

which the CB host could be encapsulated. A four carbon linker was used for its

known ability to have different binding interactions between the two CB[7,8]

hosts and sensitizer,93-93

see scheme 17.

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Scheme 17. Chemical structures of ligand p and complexes 7, 7CB[7], 7CB[8].

Complex 7 was synthesized, by reacting ligand p with 2.5 equivalents

Ru(bpy)2Cl2 in degassed H2O and stirring the solution overnight at 900

C. The

synthesis with CB[7] followed the same procedure, but with addition of CB[7]

to ligand p before reaction with Ru(bpy)2Cl2. The interaction between the

ligand and CB[7] host was easily determined both by NMR and ESMS.

Synthesis of complex 7CB[8] could not proceed in a similar fashion. Instead

a mono-ruthenium psuedorotaxane was produced with the unbound 2,2‟-

bipyridine chelate forming a charge transfer interaction with viologen moiety

inside the host cavity.

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Scheme 18. Synthetic pathway of 7CB[8]

Investigating the interaction between ligand p and CB[8], via NMR and

UV/Vis, showed that the intramolecular stabilized charge-transfer (CT)

complex between 2,2‟-bipyridine and the viologen moiety (scheme 18, p-q)

had been formed.[5d]

This CT complex was strong enough to stop the rotaxane

formation. The issue was solved via introducing a stronger electron donor, 2,6-

dihydroxynapthalene (DHN) (scheme 18, r). DHN subsequently formed a CT-

complex with viologen inside the CB[8] cavity. This interaction could easily be

confirmed via ESMS, NMR and UV/Vis measurements, where in the latter

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case, the CT band between viologen and DHN was found at 340 nm. Reaction

with cis-Ru(bpy)2Cl2 produced complex s. DHN was removed using sephadex

LH20 column chromatography. Additional cleanup steps yielded the pure

7CB[8].

Characterization of the complexes, surprisingly, showed that the host in either

case was dynamically positioned upon the carbon linker. In the case of CB[8]

some of the protons of the bi-dentate ligands were also found to interact with

the cavity of the host, see protons 9-11 marked in scheme 18. Such an

interaction with the ligands is not surprising considering the size of the host.

Electrochemistry of 7 in acetonitrile gave two successive one-electron

reduction waves, corresponding to the two redox-peaks of the viologen moiety.

For the complex 7, the first and second reduction are observed at -0.68 and -

1.10 V whereas -0.86 and -1.37 V were observed for both 7CB[7] and

7CB[8]. This similar reduction potential for both hosts indicates that no

viologen radical dimer could be created with only the formed complex.

The oxidation potential of 7 was found at 0.93V vs. Ag+/AgNO3. Surprisingly

the complexes with host gave dual oxidation potentials at 0.93 V and at a lower

potential. Ca 100 and 200 mV lower for CB[8]-[7] respectively. A likely reason

for this observation is that host positions itself close to one metal center during

oxidation as depicted in scheme 19. Measurements were performed at different

speeds from 0.01 to 3 V/s but showed no significant changes. This is assumed

to be due to the dynamic shift of the host is very fast, also indicated from the

NMR investigations.

Scheme 19. Selective positioning of the CB[7,8] host during the oxidation of

7CB[7,8] in acetonitrile.

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6.1.3. Non-aqueous photoinduced viologen radical formation

The possibility of viologen radical dimer formation based on complex

7CB[8], with and without CB[8] was one of the main reasons for this project

and was analyzed via 1H NMR, electrochemistry and photochemistry.

1 equivalent MV2+

and TEOA were added directly into the acetonitrile solution

containing the 7CB[8] and irradiated. During irradiation for 50 min, the color

of solution changed slowly from orange to dark brown. Due to the excess of

TEOA the complex retained its Ru(II) oxidation state, during the following 1H

NMR experiments, as seen in figure 15.

Figure 15. 1H NMR in CD3CN of 7CB[8]: MV2+ 1 equiv. (8.26×10-4 M) in the

presence of TEOA 5x10-2 M (a) before irradiation, (b) irradiation for 50 min and (c) expose to the air (O2).arrows indicate the shift of the atoms on the chelate

(numbered 9-11) in scheme 18.

It was observed by 1H NMR experiments, when irradiated with TEOA and

external viologen, that the CB[8] host shifted away from the metal centers

towards a more central position as the viologen units were reduced, as seen in

figure 15. This effect were not observed when free viologen was absent from

the system. Electrochemistry measurements, although complex, also indicated

a chemical process during the irradiation.

To confirm that both 1H NMR and electrochemical shift were due to 7CB[8]-

V+

+ MV+

radical dimer formation, UV/Vis spectroscopy was performed (see

figure 16). Irradiation for a total of 40 minutes, gave a typically brown colored

solution, both the radical monomer at 397 and 600nm as well as the radical

dimer absorption peaks at 370 and 555 nm and broad absorption band

around 800-1100 nm were detected (Amax=970 nm).85

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Figure 16. Absorption spectra of 7CB[8] in the presence of MV2+ 1 equiv. (6.4×10-

5 M) and TEOA (5×10-2 M) in acetonitrile before irradiation (black), irradiate for 25

(red), 40 minutes (green) and expose to the air (O2) (blue)

.

6.1.4. Conclusions

A template-based synthesis has been presented to form a rotaxane which is

able to provide the possibility to move the CB[8] host-guest complex into non-

aqueous solution with high solubility. It was found that the host could stabilize

the radical dimer system in non-aqueous solution, however preliminary results

suggest that the stabilization of the radical dimer is weaker compared to

aqueous solution.

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7.

An Efficient Water Oxidation System Based on Supramolecular Assembly of Molecular

Catalyst and Cucurbit[7]uril.

(Paper IX)

7.1. Introduction

The Oxygen evolving complex (OEC) that exist in the PS II system has

received much attention but is still one of the mysteries of nature. This

complex system is the foundation that gives plants and other photosynthetic

organisms the ability to convert sunlight to chemical energy. With the current

need to find new green energy sources, this process has received considerable

attention, as such possible energy source.96

In nature PSII is a large

homodimeric protein-cofactor complex where the water oxidation catalytic

center is a Mn4OxCa cluster surrounded by different types of proteins.97

The

precise reason of the proteins is not known but there have been suggested that

they facilitate the electron transfer via tyr z. Inspired by the OEC in PSII,

significant improvements on the turnover frequency [TOF] of Water Oxidation

Catalysts (WOC), using alternative transition metals, such as ruthenium,98-108

since the “blue dimer” was first reported by Meyer and coworkers. 98

Scheme 20. Meyers “blue dimer” (left)98 and example of a WOC with dimeric

pathway (middle) 107 and monomeric pathway (right).105

In our group we have investigated WOCs that have a TOF of up to 4/s using

Ce(IV) in pH 1 solutions. These complexes are based upon a negatively

charged backbone ligand and the ability to form dimeric complexes in water

during the water oxidation process confirmed by crystal structure and by

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theoretical calculations as seen in scheme 20.108

One problem with the WOCs

of today is the low Turn Over Number (TON), which needs a significant

increase for any practical use. For the 2,2‟-bipyridine-6,6‟-dicarboxylic acid

(dba)-based complexes, experiments have shown that, the oxidation of the two

mono dentate axial ligands is one possible reason for the degradation of the

WOCs and the low TONs.107

To solve this issue as well as investigate the

dimeric pathway; the CB[n] looked to be a prime component.

Scheme 21. Proposed mechanism for water oxidation via the bimolecular process, red arrows indicating the removal of protons.

As previously mentioned the host family has been used as catalysts to good

effect in different types of reactions.63-72

For the WOCs a host-guest interaction

with the CB[n] could have several effects. The first would be to shield the

sensitive axial mono-dentate ligands from oxidation. A secondary effect would

be to act as a second sphere ligand,109

helping in the proton transfer mechanism

away from the Ru-O…

O-Ru center, via hydrogen bonding between the

carbonyl groups on the CB[n] cavity edges and the bound water molecule

increasing the proton transfer rate.

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7.1.1. The aim of this study

The aim of this study was to explore the possibilities of regulation of a WOC

catalyst, by inclusion into a CB[7] host.

7.1.2. Design and synthetic procedures

The principle was designing two different WOC‟s with the ability to bind

towards CB[7]. By modifying two known catalysts105-107

different binding

modes towards a host were created. The host CB[7] can bind either axial close

to the reaction center (WOC 8), or away from the reaction center on the

tridentate backbone ligand (WOC 9) as shown in scheme 22.

Scheme 22. Supramolecular systems of WOC 8∙2CB[7] and 9∙CB[7].

The backbone tetra-dentate ligand for 8 was formed by oxidizing 6,6‟-

dimethyl-2,2‟-bipyridine with sodium dichromate in conc. Sulphuric acid to

form the biscarboxyl backbone ligand according to literature.110

coordination

with Ru(DMSO)4 and methylated axial ligand gave the finished product.105

The

Synthetic procedure of complex 9 was a seven step route as shown in scheme

23 below. Cheldamic acid was reacted with PBr5 forming the 4-

Bromopyridine-2,6-dicarboxylic acid dimethyl ester.111

The pyridine was

introduced by Suzuki coupling.112

Different reaction conditions (catalyst, time,

temperature, solvent) were investigated. The best choice of catalyst was

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Pd(dppf)Cl2∙CH2Cl2 due to stability. Under microwave irradiation, this reaction

showed good yields. Methylation in CH2Cl2 gave intermediate y, followed by

hydrolysis. Coordination to Ru(DMSO)4Cl2 was conducted in methanol with

TEA as base, followed by a second coordination step with 4-piccoline which

yielded WOC 9.

Scheme 23. Synthetic pathway of WOC 9

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7.1.3. Host-guest interaction

Both complexes were investigated and characterized via NMR and HRMS and

as designed, showing the possibility to hold two (WOC 8) or one (WOC 9)

CB[7] host(s). As potential water catalysts the electrochemistry is of high

importance. Cyclic voltammetry was used to determine the redox potentials of

the catalysts. WOC 8 in a PH 1 solution of TFA (Trifluorosulphonic acid) show

a reversible redox couple, assigned to RuII/Ru

III process with E1/2 being 0.76 V

vs. NHE. A slight oxidation ridge can be detected at around 1.23 V vs. NHE.20

Complex 9 shows as its analogue107

two oxidation potentials at 100mv/s

depending on solvent interaction, When CB[7] was added to the solutions a

slight decrease of the oxidation potential of 0.03-0.04 V was detected for the

RuII/III

redox potential in both cases.

7.1.4. Catalytic water oxidation

The catalytic water oxidation was performed utilizing a simple two-component

molecular system consisting catalyst and Ce(IV)(aq.) as an oxidant in pH 1.0

aqueous solution, see scheme 24.

Scheme 24. Catalytic water oxidation using molecular catalysts 8 and 9.

The oxygen formation through water oxidation was measured with an oxygen

sensor, while continuous GC measurements were performed to measure the

amount of oxygen generated.106-107

Table 2. Dioxygen evolution rates using Ce(IV) as oxidant

complex TON[a]

Rate[b]

8 600 0.99[c]

8∙2CB[7] 1486 2.11[c]

9 300 1.20[c]

9∙CB[7] 300 1.18[c]

[a] Measured by oxygen sensor and calibrated by GC. [b] Initial rate in turnover/s. [c] A linear fitting of the first 3 minutes for 8 and 5

minutes in the case of 9 was used to obtain the rate.

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The expectations from this inclusion were to find a lower TOF due to change

in mechanism, where the host-guest system is unable to form the dimer with

the bulky host, as well as an increased TON due to the protected axial ligands.

In the case of 8∙2CB[7] not only did we detect a better TON but also a faster

TOF compared to 8 alone. In the case of 9∙CB[7] and 9 however, no

significant changes could be seen, see table 2 and figure 17.

0 500 1000 1500 2000

0

20

40

60

80

100

120

140

mic

rom

ol O

2 fo

rme

d

Time/s

82CB[7]

8

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5

-10

0

10

20

30

40

50

60

mic

rom

ol O

2

Time (h)

9

9CB[7]

Figure 17. (left) Oxygen evolution of complex 8 and 8∙2CB[7] recorded in gas phase

by oxygen sensor and calibrated by GC. (Right) Oxygen evolution of complex 9 and 9∙CB[7] recorded in gas phase by oxygen sensor and calibrated by GC.

To understand the high TON and TOF of the 8∙2CB[7] assembly, it was

investigated kinetically via UV/Vis where the absorption decay of Ce(IV)

could be monitored at different concentrations, see figure 19,106-107

when

combined into one graph the rate dependence on concentration could be

observed, as shown in figure 18.

0,5 1,0 1,5 2,0 2,5 3,0

0,5

1,0

1,5

2,0

2,5

3,0

Ko

bs x

10

6 (

Ms

-1)

[1] x 10-6 [M]

pure

2 equiv

Figure 18. Plot of the initial rate (kobs) vs. concentration of complex 8 with and without CB[7]. The initial kobs was calculated from the first 60 seconds data of the

kinetic experiments

The kinetic measurements indicated that there are two different pathways. In

the case of 8 a second order mechanism was observed, as its analogue (scheme

17, middle). In the case of 8∙2CB[7] a first order mechanism was detected.

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Possibly due to the size of the CB[7] hindering the dimerization, between two

8∙2CB[7] systems.

7.1.5. Theoretical calculations

To understand the higher TOF of 8∙2CB[7] above 8 alone, theoretical analysis

was performed on a simplified system of 8∙1CB[7], as shown below in figure

19. The theoretical calculations did indeed show a significant hydrogen

bonding interaction. The distance between the CB7 carbonyl oxygen and

hydroxyl proton was calculated to 1.8 Å indicating a significant hydrogen

bonding interaction.

Figure 19. Optimized geometry (M06-L/LACVP)113 of a model complex containing one tmebipy+Cl- ligand binding to a CB7.

7.1.6. Conclusions

The theoretical data, based on a simplified structure clearly show that the

system could hinder the dimerization process. Kinetic measurements indicate a

possibility for the complex to proceed via a mono-mechanism compared to

dimer based mechanism without host. That complex 9 has no increase or

change in TOF or TON proves the importance of the positioning of the host.

Further research is in progress with the supramolecular catalytic systems.

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8. Concluding Remarks

The number of possible uses of the cucurbit[n]uril host is almost infinite. In the

introduction I have described several different types of uses, like catalysis,

drug treatment as well as molecular machines.

My work, presented here, has been based upon the goal of understanding the

host‟s interaction with different ruthenium based photosensitizers. As always

there are many paths within even this narrow field that are yet to be explored.

We have explored the ET transfer and stabilizing abilities of the host when

ruthenium is connected with phenols, viologens to name a few. The host is also

clearly stabilizing these complexes, preventing degradation. We have also

shown several instances of molecular machines, however the supramolecular

machine in its classic sense is still far away from practical uses.

It is hard to debate where the first practical industrial use of the host will

emerge. However due to the low toxicity, I believe that the pharmaceutical

industry will be the first to benefit from the host.

Catalytic uses are I assume already in use in laboratories due to the multitude

of publications within this field. It is my hope that our work with water

oxidation catalysts, catalyzed and stabilized by CB[7] will be one of the

processes that are industrialized.

.

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Acknowledgements

I would like to express my gratitude to:

Professor Licheng Sun. Thank you for accepting me as a PhD student and for

your guidance as well as your happiness.

The Swedish Research Council, Swedish Energy Agency and the K & A

Wallenberg foundation for financial support of this study.

The Aulin Erdmann foundation for funding to make it possible for me to go to

several conferences.

Also past and present group members and for fruitful discussions and

collaborations; Yunhua Xu, Daniel Hagberg, Peng Quin, Lele Duan, Shiguo

Sun, Dapeng Zou, Martin Karlsson, Erik Gabrielsson, Lianpeng Tong, Mikhail

Gorlov, Haining Tian, Fuyu Wen, Xien Liu. This is truly a wonderful group of

people.

Also Jingxi Pan and Rong Zhang for help with kinetic measurements as well as

HRMS.

A special thank you to professor Torbjörn Norin, Juho Bah, Lele Duan and

Yunhua Xu for valuable comments of this thesis.

Lena Skowron, Henry Challis and Ulla Jacobsson for help with practical

matters.

All past and present coworkers on the Organic chemistry department

My friends; for the good times.

Mom, Dad and my brothers and sister and my older brothers daughter Lea.

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51

Appendix A

The following is a description of my contribution to Publications I to IX, as

requested by KTH.

Paper I: Minor contribution to the formulation of the research problems.

Performed parts of the synthesis as well as performed a majority of the UV/Vis

electrochemistry measurements and wrote parts of the manuscript.

Paper II: Minor contribution to the formulation of the research problems.

Performed parts of the synthesis as well as performed a majority of the UV/Vis

measurements and wrote parts of the manuscript.

Paper III: contributed to the formulation of the research problems. Performed

parts of the synthesis and measurements as well as wrote the parts of the

manuscript.

Paper IV: Major contribution to the formulation of the research problems.

Performed the synthesis and measurements as well as wrote the manuscript.

Paper V: Major contribution to the formulation of the research problems.

Performed the synthesis and measurements as well as wrote the manuscript.

Paper VI: Major contribution to the formulation of the research problems.

Performed parts of the synthesis and measurements as well as wrote parts of

the manuscript

Paper VII: Major contribution to the formulation of the research problems.

Performed parts of the synthesis and measurements as well as wrote parts of

the manuscript.

Paper VIII: Major contribution to the formulation of the research problems.

Performed parts of the synthesis and measurements as well as wrote the parts

of the manuscript.

Paper IX: Major contribution to the formulation of the research problems.

Performed the synthesis and measurements as well as wrote the manuscript.

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calculations were performed with Jaguar 7.6 by Schrodinger LLC. See supporting

information for more details.