2,616 research outputs found
Copper(I) polypyridine complexes. the sensitizers of the future for dye-sensitized solar cells (DSSCs)
No full textThe thesis concerns the development of novel dyes for the photosensitization of titanium
dioxide for incorporation into dyes-sensitized solar cells (DSSCs). The majority of dyes
utilized to date are based upon heavy transition metals such as ruthenium. Although these
are efficient (>10%), they have disadvantages in the cost of the materials and also in the
availability of the very rare platinum group metals. The thesis investigates the use of
copper(I) complexes of oligopyridines, which are known to have similar photophysical
properties to ruthenium(II) tris(oligopyridine) species but which have not been widely
used in solar cells. The labile nature of the copper(I) centre precluded previous systematic
investigation of the complexes for this application.
Synthetic methods for a series of carboxylate and phosphonate functionalized 2,2'-
bipyridine ligands with substituents at the 6- and 6'-positions have been developed. The
carboxylate or phosphonate functionality is required for the binding of the ligands and
complexes to the titanium dioxide surface and the substituents adjacent to the nitrogen
stabilise the photoexcited state with respect to quenching and oxidation.
DSSCs were prepared using the basic protocols established for ruthenium dye-sensitizers,
involving the doctor-blading of a TiO2 paste onto an ITO or FTO electrode followed by
annealing, absorption of the dye and cell construction with conventional iodide-triiodide
electrolyte. The cells were tested in Basel using a home-built cell tester or a modified
scanning electrochemical microscope and in Lausanne at the EPFL in the laboratory of
Prof. Michael Graetzel using an industry standard protocol. The surprising results were
that the copper-functionalised DSSCs had efficiencies approaching 2.5% for the
prototype compounds.
The lability of the copper(I) complexes has allowed us to develop an entirely novel
strategy for the design of solar cells in which the carboxylated or phosphonated ligand L
is first attached to the TiO2 surface and subsequently metallated by reaction with any
[CuL'2] complex to give a surface bound [CuLL'] species and the method is likely to lead
to the future use of libraries of complexes to achieve full spectrum coverage rather than
the design of "black" dyes
Octyl-decorated Fréchet-type dendrons : a general motif for visualisation of static and dynamic behaviour using scanning tunnelling microscopy
No full textFirstly, a short overview on supramolecular chemistry including definitions, basic principles and examples taken from the literature of 2D and 3D self-assembly processes is given in Chapter 1. The introduction is completed by some general ideas of dendrimer chemistry. In the second Chapter the techniques used in this thesis are introduced with a special focus on scanning tunnelling microscopy (STM). Besides the mode of operation and the data processing, the historical background is briefly described. The following four Chapters present STM studies of monolayers formed by different types of compounds, all functionalised with Fréchet-type dendrons. Not only static features of monolayers such as conformational analysis of single molecules have been investigated, but also dynamic processes such as delayed conversion of a whole domain and conformational changes by protonation have been examined. The 2D properties of monolayers on a graphite surface have been compared with the X-ray data of 3D single crystals. For two compounds, the same molecular arrangement has been detected in monolayers on graphite and in single crystals. Together with organic molecules, the self-assembly of metal complexes possessing tpy ligands and organometallic species with platinum(II) bis(alkynyl) units has been examined. Not all of these metal complexes were stable under the scanning conditions used in STM. A synthetic programme leading to dendrimer-functionalised organic and organometallic compounds has been developed. Discussions of synthetic routes are given at the beginning of each Chapter. Chaptercompares X-ray diffraction methods with STM, the two main analysis tools used for investigation of self-organised assemblies in the solid state in this thesis. In the second part of Chapter 7, the results presented in the previous Chapters are discussed with some general reflections on the self-assembling properties of Fréchet-type dendrimers with pendant octyl groups. Additional to the studies of self-assembled monolayers, the formation of metallomacrocycles has been investigated using two novel homoditopic tpy ligands. This work is presented in Chapter 8. It was demonstrated that the ring-size depends on the metal used for the cyclisation. Furthermore, some of the macrocycles formed self-assembled monolayers on graphite, which have been examined using STM. One homoditopic ligand formed a molecular square by complexation with an iron(II) salt which was analysed using single crystal X-ray diffraction. This thesis has brought together the realms of chemical design with studies of the physical behaviour of the envisioned molecules on the surface. It has been demonstrated that Fréchet-type dendrimers with octyl end-groups are a general motif for visualisation of static and dynamic behaviour using STM
New oligopyridine ligands for transition metal complexes and their applications
No full textThis thesis concerns the synthesis of polypyiridine ligands, their use for preparation of
transition metal complexes and finally, the application of the transition metal complexes for
Dye Sensitized Solar Cells (DSCs) and Light Emitting Electrochemical Cells (LECs).
Chapter 1 gives a short introduction of the ligands, the metal complexes which were
involved in this work, as well as, their applications.
Chapter2 defines the objectives of this work.
Chapter 3 describes the synthetic approaches to new polypyridine ligands with either the
classical KRÖHNKE method or with less used and for some substituents not reported methods.
These include direct coupling of lithium organyls or the Jahng reaction, followed by the
discussion of their characterization and properties.
Chapter 4 describes the synthesis of homoleptic copper(I) complexes and their
characterization. Difficulties with NMR experiments and the reason thereof are discussed in
detail along with electrochemical experiments. Their use in the preparation of DSCs is given
at the end of this chapter.
Chapter 5 regards the synthesis and characterization of novel iridium(III) complexes, as well
as, the results for some LECs devices.
Chapter 6 shows the results obtained with novel ruthenium(II) complexes based on new bpy
or tpy ligands, respectively. ----------
Parts of this work have been published:
B. Bozic‐Weber, E. C. Constable, C. E. Housecroft, P. Kopecky M. Neuburger, J. A. Zampese,
Dalton Trans. 2011, 40(46), 12584. --
E. C. Constable, C. E. Housecroft, P. Kopecky, M. Neuburger, J. A. Zampese, G. Zhang,
CrystEngComm 2012, 14(2), 446. --
E. C. Constable, C. E. Housecroft, N. Hostettler, P. Kopecky, M. Neuburger, J. A. Zampese,
Dalton Trans. 2012, 41, 2890
How structural factors influence the performance of copper(I) bis(diimine) based DSCs
No full textAbstract
This PhD thesis is based on the synthesis of new homoleptic copper(I) complexes and their applications in dye-sensitized-solar-cells (DSCs).
Chapter I: Is an evaluation of the anchoring ligands effect upon device performance containing ancillary ligands of 1st and 2nd generation hole transport triphenylamino-dendrons.
Chapter II: Describes the influence of six different substituents in the 6,6’-positions of the ancillary ligands on the device performance.
Chapter III: Is a short study of a more atom economic device assembling method, where the copper(I) complex is formed in situ on the TiO2 surface.
Chapter IV: Shows the influence of the dye conentration used during the dyeing process of the semi-conductor.
Chapter V: Is a study of how the enhanced photon absorption, achieved by extending the aromatic system of the ancillary ligand, affects the cell performance.
Chapter VI: Describes the use of different solvents during the dyeing process of the photoanode and their influence on DSC performance.
Chapter VII: Addresses issues concerning the TiO2 surface such as the aggregation of dye molecules and how the addition of co-adsorbants during the dyeing cycle may prohibit the formation of such aggregates.
Parts of this work have been published:
• B. Bozic-Weber, S. Y. Brauchli, E. C. Constable, S. O. Fürer, C. E. Housecroft and I. A. Wright, Phys. Chem. Chem. Phys., 2013, 13, 4500-4504.
• B. Bozic-Weber, S. Y. Brauchli, E. C. Constable, S. O. Fürer, C. E. Housecroft, F. J. Malzner, I. A.Wright and J. A. Zampese, Dalton Trans., 2013, 34, 12293-12308.
• S. Y. Brauchli, B. Bozic-Weber, E. C. Constable, N. Hostettler, C. E. Housecroft and J. A. Zampese, RSC Advances, 2014, 4, 34801-34815.
• S. Y. Brauchli, F. J. Malzner, E. C. Constable and C. E. Housecroft, RSC Advances, 2014, 4, 62728-62736.
• S. Y. Brauchli, E. C. Constable, C. E. Housecroft, Dyes and Pigments, 2015, 113, 447-450.
Summary
Within this study, 18 ligands (L1.1-L3.6) and their homoleptic copper(I) complexes [Cu(L1.1-L3.6)2][PF6] have been synthesized. They were fully characterized by 1H and 13C NMR, mass spectrometry, solution absorption spectrometry, melting point, elemental analysis and infrared spectrometry. Furthermore, all homoleptic Cu(I) complexes were electrochemically analysed by cyclic voltammetry and square-wave voltammetry.
By increasing the aromatic system in the ligands (Scheme 26), the light harvesting was effectively enhanced (e.g. going from L1.1 -> L2.1 -> L3.1). An increase in absorption by extending the aryl system was achieved in the homoleptic Cu(I) complexes, with an extinction of about twice that the free ligands.
Scheme 26: Representative ligands to illustrate the extension of the aryl system.
Furthermore, the substituents in the 6,6´-positions on the bipyridine were varied within each ligand generation (Scheme 26). All complexes were incorporated in DSCs.
In Chapter I, the first focus is on the influence of the anchoring ligand on the performance of a DSC. For this study, two representative capping ligands were introduced by treating an anchoring ligand covered photoanode with complexes [Cu(L2.1)2][PF6] and [Cu(L3.1)2][PF6]. By using these two example dyes, a set of four anchoring ligands was screened to identify the one that yielded the best conversion efficiency in the device.
Scheme 27: Set of anchoring ligands with phosphonic and carboxylic acids as anchoring groups.
It turned out that devices with anchoring ligands decorated with phosphonic acids (ALP and ALP1) generally achieve higher efficiencies than those with carboxylic acids (ALC and ALC1). Additionally, the influence of the extended aryl system on the ancillary ligands (L2.1 vs. L3.1) was examined in this set. Indeed, higher conversion efficiencies were obtained from devices incorporating the more conjugated ancillary ligand L3.1 compared to L2.1.
Scheme 28: Ancillary ligands L1.1-L1.6 examined in Chapter II.
In Chapter II, the influence of 6 different substituents in the 6,6’-positions of the bipyridine ancillary ligands (Scheme 28) in combination with anchoring ligands ALP and ALP1 was examined. It was found that DSCs incorporating anchoring ligands ALP1 reach much higher conversion efficiencies than those with ALP. Ancillary ligands L1.3 and L1.5 reached remarkably higher efficiencies, which was attributed to the reduced charge recombination rate.
Scheme 29: Two approaches to introduce a copper metal ion and an ancillary ligand on a TiO2 coated photoanode.
In Chapter III, a new strategy for incorporating heteroleptic complexes on the TiO2 surface was tested and compared with the state of the art methodology. The state of the art method works as followed. After an anchoring ligand has been adsorbed on a semiconductor surface, the photoanode is immersed in a solution of homoleptic Cu(I) complex. Due to the labile nature of Cu(I) complexes, a ligand exchange with the previously anchored ligand occurs, leaving with heteroleptic copper dye on the surface.
In the second methodology it becomes needless to prepare the homoleptic Cu(I) complex beforehand. By using the new method (stepwise methodology), an additional step during the dyeing process is required. Nevertheless, it is more economic than the conventional process. After the anchoring ligand is bound to the TiO2 surface, the anode is immersed in a solution of [Cu(MeCN)4][PF6]. At this stage the copper(I) binds to the anchoring ligand and it is assumed that a heteroleptic complex with two coordinating acetonitrile molecules is formed. In the last step, the anode with the intermediate heteroleptic complex on the surface is immersed in a solution of pure ligand, which replaces the acetonitrile molecules due to the chelating effect. The main outcome of this survey was that devices prepared by the state of the art method achieve a higher final conversion efficiency than those prepared from the stepwise assembly. However, using this new method, devices exhibited a higher initial efficiency than those prepared from the old method.
In Chapter IV, devices were prepared from four different concentrations of dye solutions ([Cu(L2.1)2][PF6] in CH2Cl2 at 2.0, 1.0, 0.5 and 0.1 mM). Their initial efficiencies and their development over several days were compared. The results showed that devices prepared from the least concentrated dye solutions reached their maximum efficiency immediately after assembling the cells and this efficiency was maintained over the whole measuring period. Additionally, it was found that DSCs prepared from the more dilute dye solutions reach a higher maximum conversion efficiency than those prepared from concentrated dye solutions.
In Chapter V, the focus was on the change in device performance by extending the aromatic systems of the ancillary ligands. Ligands L2.1-2.6 and L3.1-3.6 were introduced into the DSCs by applying the state of the art ligand exchange method using complexes [Cu(L2.1-2.6)2][PF6] and [Cu(L3.1-3.6)2][PF6]. Except for ancillary ligand L3.1, no increase in efficiency was recorded by extending the aromatic system and increasing the absorption. Although the solid state UV-vis absorption spectra of the photoanodes showed an increase in absorption intensity, no gain in Jsc was achieved.
Chapter VI addresses the use of two different solvents during the dyeing process of the photoanodes. The cells were prepared either from acetone or CH2Cl2 dye solutions of [Cu(L2.1-2.6)2][PF6] and [Cu(L3.1-3.6)2][PF6]. By measuring solid state absorption spectra of dye loaded photoanodes, it turned out that upon using acetone during the dyeing process a severe increase of dye adsorption on the TiO2 surface was achieved. Moreover, by using acetone dye solutions the devices incorporating the more conjugated ancillary ligands (L3.1-3.6) reach generally higher efficiencies than cells with ligands L2.1-L2.6. DSCs prepared from acetone dye solutions containing capping ligands L3.1-3.6 also exhibit higher efficiencies than those with the same ancillary ligands prepared from CH2Cl2 solutions. For devices with capping ligands L2.1-2.6, no clear trend could be discovered by comparing cells prepared from acetone and CH2Cl2 dye solutions.
In Chapter VII, the main attempt was to minimize the dye aggregation on the surface by adding a co-adsorbant (chenodeoxycholic acid) to the dye solution during the dyeing process of the photoanode. The homoleptic complexes [Cu(L3.1)2][PF6] and [Cu(L3.5)2][PF6] served as example dyes. Additionally, cells were prepared again from acetone and CH2Cl2 dye solutions. Interestingly, all devices prepared from CH2Cl2 in the presence of cheno showed a clear increase in efficiency compared to the control devices without co-adsorbant. Furthermore, the device with ancillary ligand L3.5 prepared from acetone dye solution with cheno showed a higher conversion efficiency than its control cell. The device with the capping ligand L3.1 obtained from an acetone dye solution with cheno did not show an increased performance.
Conclusion
It has been shown that by increasing the aromatic system of the ancillary ligand, a gain in absorption intensity and an increase in conversion efficiency was achieved under certain circumstances. The studies revealed the huge number of possible tuning sites of DSCs, such as structural properties of the dye, dye concentration and solvent used during the dyeing cycle, and aggregation issues concerning the molecular size of the dye. Nevertheless, this work showed that a dye that does not seem to yield a reasonable conversion efficiency at first might reveal its full potential after some time. Screening of dyes is quite delicate because it is simply impossible to know the optimal conditions for every dye and it is likely to miss a potentially good dye.
Outlook
For the future, one may want to think to test more solvents during the dyeing process of the photoanode in order to obtain even higher device performances. Additionally, it might be reasonable to add a co-adsorbant to all of the synthesized dyes during the dyeing process of the photoanode in order to reduce dye aggregation, reduce charge recombination and increase the efficiency. Furthermore, that it is also sensible to test new electrolytes in combination with these dyes in attempt to obtain, for example, a higher Voc
From self assembled monolayers to clickable gold nanoparticles
No full textThe aim of the present PhD thesis was the investigation of the behavior of gold nanoparticle stabilizing oligo thioether ligands on gold surfaces and further on to develop a protocol for the directed assembly of mono functionalized gold nanoparticle into defined oligomer structures.
Outline
The present cumulative PhD thesis consists of the following parts:
In the Introduction the research field of gold nanoparticles is presented with to point out their unique electronic and physical properties. The second focus will be on the controlled interlinking and functionalization of gold nanoparticles using click chemistry and their potential applications, which will be submitted as a review article.
Within Concept and Strategy the goals of the research project are introduced and the concepts and outputs of the resulting publications are presented.
The Publications are accumulated with their respective Supporting Information, in the order in which they were prepared:
“Loops versus Stems: Benzylic Sulfide Oligomers Forming Carpet Type Monolayers“ F. Sander, T. Peterle, N. Ballav, F. Wrochem, M. Zharnikov, M. Mayor J. Phys. Chem. C, 2010, 114, 4118 – 4125.
“Add a Third Hook: S-Acetyl Protected Oligophenylene Pyridine Dithiols as Advanced Precursors for Self-Assembled Monolayers“ F. Sander, J. P. Hermes, M. Mayor, H. Hamoudi, M. Zharnikov PCCP, 2013, 15, 2836 – 2846.
“Dumbbells, Trikes and Quads - Click Gold Nanopartricles together“ F. Sander, U. Fluch, J. P. Hermes and M. Mayor Small 2014, 10, 349 – 359.
“Click Chemistry with Gold Nanoparticles – A Tool for Functionalization, Interlinking and Labeling” Fabian Sander and Marcel Mayor, manuscript prepared for submission.
Finally, within Conclusion and Outlook the main results are briefly summarized and further potential research is proposed
The application of Cu(I) phenanthroline dyes in DSCs with optimized I⁻/I₃⁻ and Co(II/III) electrolytes
No full textThe world faces an energy and climate crisis. After an unprecedented worldwide increase in energy consumption, which has largely been based on the use of fossil fuels, mankind is challenged by global warming and its consequences. The demand for renewable energy has focused our attention on capturing the inexhaustible solar energy. Photovoltaic (PV) devices based on silicon have been and remain the most popular choice. However, the high purity demands of this technique are a drawback for cheap energy production from solar power. Dye sensitized solar cells (DSCs) are a valuable alternative for low-cost PVs since the separation of light-harvesting and charge transport implicates less stringent purity demands of the built-in compositions. Replacing rare ruthenium used in Grätzel-type n-type DSCs by more Earthabundant and sustainable metals is a goal of our research group. This thesis describes the use of heteroleptic Cu(I) dyes using phenanthroline ancillary ligands to harvest light.
Chapter 1 gives a short overview of the current energy problems and outlines the current status of the literature relevant to this thesis. Chapter 2 describes the methods for the characterization of the investigated dyes and their application in dye sensitized solar cells (DSCs). Chapter 3 shows the synthesis and characterization of ligands and of copper(I) complexes designed for application in DSCs. Chapter 4 compares the performances of DSCs containing heteroleptic Cu(I) complexes made from [Cu(13)2][PF6] (ligand 13 contains a peripheral hole-transporting NPh2 group) and four different anchoring ligands with carboxylic acid (ALC1) or phosphonic acid (ALP, ALP1 and ALP1 TBA) anchors. Chapter 5 investigates the differences between heteroleptic Cu(I) dyes from several phenanthroline based ancillary ligands in combination with anchoring ligand ALP1. Chapter 6 deals with the optimization of I−/I3− electrolytes for [Cu(15)(ALP1)]+ sensitized solar cells (ligand 15 contains a peripheral hole-transporting domain related to that in ligand 13). Chapter 7 shows the incorporation of [Co(bpy)3][PF6]2/3 electrolyte in DSCs using [Cu(13)(ALP1)]+ and [Cu(15)(ALP1)]+ sensitizers. Chapter 8 lists the experimental details. Chapter 9 concludes the work and gives an outlook for future work
Part I: Characterization of Cr3C2-25% NiCr reactive plasma sprayed coatings produced at different pressures
No full textThe present work was performed with the aim of characterizing various plasma sprayed Cr3C2-NiCr coatings produced by using different processing pressures between 300 and 1200 mbars, in a nitrogen controlled atmosphere CAPS system. X-Ray diffraction was carried out on all coatings by using Bragg-Brentano geometry. The phases identified in the as-supplied powder Cr3C2/Ni-Cr were fcc Ni-Cr and orthorhombic Cr3C2. In contrast to the original powder, the coatings showed evidence of Cr3C2, Ni-Cr and either Cr6.2C3.5N0.3 or Cr3C1.52N0.48 carbo-nitride phases depending on the ratio of C/N in the coating. The presence of Cr7C3 and CrO2 was also identified in the coatings deposited at atmospheric pressure. The volume fraction of carbide plus nitride phase in the coating was always less than the volume fractions of the carbide phase in the original feed stock powder. The volume fraction of carbide plus nitride phase was found to depend quite markedly on the spraying parameters such as pressure, power input, spraying distance and substrate cooling. The results have been presented in terms of spraying efficiency, ξ. The highest value of ξ (86.4%) was obtained for coatings produced at 1200 mbar pressure, a spraying distance of 120 mm, without N2 cooling and the lowest value (25.2%) was found for the coatings deposited at 300 mbar for the same spraying distance but with N2 cooling. The presence of graphitic carbon was detected in all samples especially for specimens where the fraction of carbide plus carbo-nitride phases was the greatest. The influence of spraying parameters such as pressure, power input, spraying distance and substrate cooling on the microstructure was determined. The highest microhardness value of 2296 HV50 was found for the carbide plus carbo-nitride phase contained in the specimens produced at 1200 mbar spraying pressure, 120-mm spraying distance and substrate heating at 600°C. © 2001 Elsevier Science B.V. All rights reserved
Self-assembled photonic mesostructures for water splitting photoanodes
No full textSolar water splitting is a relevant principle for the production of green hydrogen fuel. A wealth of different designs has been envisioned to produce hydrogen using sunlight. Among those designs photoelectrochemical water splitting offers possible advantages regarding components integration and costs. This technology requires blending many materials requirements in a single component, such as solar light absorption, high electric conductivity, resistance to photocorrosion, and electrocatalytic properties. To achieve this goal it is necessary to build materials with emerging properties by discovering complex architectures at the micrometric and nanometric scales that can overcome bulk material limitations.
Materials of interest for application as photoanode for photoelectrochemical water splitting are metal oxides because of their resistance to corrosion. In this thesis I focused on two of these oxides, namely hematite (alpha-Fe2O3) and monoclinic tungsten oxide (mWO3) since these materials have a relatively narrow band gap allowing absorption of a significant part of sun's irradiance. In a photoanode they were implemented as thin films on a conductive substrate. I proposed to investigate inexpensive and upscalable structuration processes for the formation of such photoanodes thin films with a controlled microstructure and studied the impact of such structures on the film photoelectrochemical performance.
Self-assembly strategies are bottom-up approaches which allow to grow structures with original morphologies at a low cost compared to top-down techniques such as lithography. I was particularly interested in strategies that would grant a fine control of the feature sizes. Two different processing techniques were implemented, a polymer templated sol-gel route and electrohydrodynamic lithography. Both techniques allowed to obtain metal oxides structures at the meso- to nanoscale. The polymer templated sol-gel route was the most successful strategy. It allowed to produce microspheroids with a tungsten oxide core and a hematite nanometric overlayer with control on the structure dimensions.
In addition to an in depth understanding of the different bottom-up approaches investigated, I proposed a complete description of the relationship between form and function in the film composed of tungsten oxide / hematite microspheroids. These films have significant photonic features linked to their original morphology and I discussed how their photoactivity is influenced by light trapping in these films
From STM to LEECs. syntheses and applications of multifunctional bipyridine ligands and their iridium(III) complexes
No full textThe theoretical background for this thesis is given in Chapter 1. It covers the field of supramolecular chemistry including the phenomena of self-assembly, the history and synthesis of dendrimers, the concept of coordination chemistry and the chemistry of iridium, the history and principles of the scanning tunnelling microscope (STM), and the theory and applications of solid state lighting, especially of the light-emitting electrochemical cells (LEECs). The background chapter is followed by a short introduction to the materials, methods, and instruments used in this thesis (Chapter 2). In the following two chapters, the syntheses of achiral and chiral Fréchet dendrimers (Chapter 3) and the subsequent reactions to the achiral and chiral Fréchet dendronised 2,2'-bipyridine ligands (Chapter 4) are described. Additionally, for most of the compounds presented in these chapters, the monolayer behaviour on graphite was studied with STM. For example, for 3,5-bis(dodecyloxy)phenylmethanol, a very highly resolved image could be detected and detailed considerations of the adopted monolayer could be performed. Chirality was introduced into the molecules for the purpose of altering the preference for a particular conformation, as it has been shown before by L. Scherer[1] that these type of ligands tend to adopt different conformations when adsorbed on graphite. Unfortunately, the measurements of the chiral ligands did not reveal any significant information. Therefore, no detailed discussion of the conformations in the monolayer could be given. Nevertheless, in a monolayer of the diastereomeric mixture of 4,4'-bis(1-(3,5-bis(dodecyloxy)phenyl)propoxy)-2,2'-bipyridine, two clearly differing patterns could be observed which were attributed to different stereoisomers. Chapter 5 deals with the synthesis of dendrons decorated with perfluorinated alkyl chains and their use in the functionalisation of 2,2'-bipyridine ligands. Adsorbed monolayers on graphite of such a ligand were studied with STM. Due to a, apparently, lower propensity to establish monolayers, only few examples of visualised patterns could be observed. The following three chapters cover the synthesis and STM-visualisation of 2,2'-bipyridine-based ligands (Chapter 6), their iridium(III) complexes (Chapter 7), and the use thereof in LEEC devices (Chapter 8). In Chapter 6, simple and more advanced ligands were synthesised and characterised. In the case of the ligands which were functionalised with dendrons presented in Chapter 2, STM studies of monolayers on graphite are discussed. Chapter 7 presents the synthesis and characterisation of iridium(III) complexes obtained from ligands described in the previous chapter. The characterisation comprises measurements of NMR, MS, UV-Vis, photoluminescence, electrochemistry, and, where single crystals could be obtained, their solid state structures. For the complexes bearing dendronised ligands, STM measurements were performed which revealed highly resolved patterns. In the last chapter (Chapter 8), results from LEEC devices fabricated with complexes described in Chapter 7 are shown. The device preparation and the measurement of their characteristics were performed by the group of H. Bolink who kindly allowed the publication of their results in this thesis. It could be shown that for all complexes exhibiting an intramolecular π-π stacking, the stability of their devices was increased dramatically. This thesis has brought together the realms of chemical design with, firstly, studies of the physical behaviour of the envisioned molecules on the surface and, secondly, systematic structural optimisation of iridium(III) complexes for the application in solid state lighting. With the work presented in this thesis, a major breakthrough for long-lived LEECs has been achieved allowing lifetimes of several thousands of hours, an increase of several orders of magnitude compared to the best-performing devices reported to date (see Chapter 1 and Chapter 8)
Manipulating connecting nodes through remote alkoxy chain variation in coordination networks with 4′-alkoxy-4,2′:6′,4″-terpyridine linkers
No full textThe effects of increasing the length of the alkoxy substituent in 4′-alkoxy-4,2′:6′,4′′-terpyridines when they are combined with cadmium(II) nitrate under conditions of room temperature crystallization and in the same cadmium : ligand (1 : 3) ratio have been investigated. The divergent ligand 4′-n-propoxy-4,2′:6′,4′′-terpyridine (2) reacts with Cd(NO3)2·4H2O to give [{Cd2(NO3)4(2)3}·3CHCl3]n in which the Cd atoms act as 3-connecting nodes and assemble into a (6,3) net with each ligand 2 linking adjacent Cd atoms. One of the three independent n-propoxy groups nestles into a cleft in the next 2-dimensional sheet; this ‘tail-in-pocket’ interaction restricts the length of the alkyl chain that can be accommodated. Replacing the n-propoxy by an n-pentoxy, n-hexoxy or n-heptoxy substituent results in a switch from a (6,3) to (4,4) net; in [{Cd2(NO3)4(3)4}·3CHCl3]n (3 = 4′-n-pentoxy-4,2′:6′,4′′-terpyridine) and [{Cd2(NO3)4(4)4}·CHCl3·MeOH]n (4 = 4′-n-hexoxy-4,2′:6′,4′′-terpyridine), each Cd atom is a 4-connecting node with trans-nitrato ligands, while in [{Cd(NO3)2(5)2}·2MeOH]n (5 = 4′-n-heptoxy-4,2′:6′,4′′-terpyridine) a cis-arrangement of nitrato ligands is observed. The reaction between Cd(NO3)2·4H2O and 4 was also investigated using a 1 : 1 ratio of reagents; this leads to the assembly of the 1-dimensional ladder [Cd2(NO3)4(MeOH)(4)3]n in which each Cd atom is a 3-connecting node. In each structure, face-to-face π-stacking of the central pyridine rings or of pyridine/phenyl rings of ligands in adjacent sheets or chains is a primary packing interaction; the role of van der Waals interactions as the chain length increases is discussed. Powder diffraction confirmed that each coordination polymer or network characterized by single crystal X-ray crystallography was representative of the bulk sample. The solid-state emission properties of ligands 2, 3 and 4 and their coordination polymers are reported; the blue emission of the free ligands is red-shifted by up to 59 nm upon formation of the coordination networks, and quantum yields are in the range 11–22%
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