Reflexivity and the process of maturation of students in a work-based learning programme

This thesis presents the outcomes of a five-year ethnographic research project of a work-based learning programme, the BA in Social Pedagogy (hereafter, the BA), which was provided in partnership with a university by a residential school for vulnerable children and young people (hereafter, the School) to its workers. The aim of the research was to develop an understanding of how the organisational fields of the School influenced learning practices and identities of workers undertaking the BA (hereafter, students). Two theoretical frameworks, of Pierre Bourdieu and Margaret Archer, were applied consecutively in the analysis of collected data. Bourdieu’s theory of practice, applied first, allowed an investigation of the conditioning by the School’s organisational fields of students’ dispositions and actions, as well as of a function of the BA in the mechanism of social reproduction of the School’s communities. Limitations of Bourdieu’s theoretical framework in examining students’ personal transformations in the course of their work and studies prompted a turn to Archer’s Morphogenetic Approach and theories of reflexivity and personal development. Re-analysis of collected data indicated that the expansion of the BA curriculum triggered and then sustained cultural and structural changes in the School. Such changes created enabling conditions for the process of maturation of students, with the BA educational practices and School work practices facilitating this process. This research project contributes to the field of applied sociological studies. Firstly, it develops an explanatory theory of processes at a work-based learning programme and its hosting institution. Secondly, it demonstrates that Archer’s theoretical framework presents methodological and analytical advantages, compared to Bourdieu’s theory of practice, for the investigation of social phenomena both on the level of an institution and on the level of individual actors, in particular when the institution undergoes cultural and structural changes and the individuals are progressing in their maturational development

Metaphors of Work-based Vocational Education for Residential Care

Within an ethnographic study of effects of organisational cultures on work-based learning, two students’ practice portfolios and interviews were analysed applying Bourdieu’s theoretical tools. Analysis pointed to two types of habitus, one being characterised by the student’s propensity to immerse herself in the “lifespace” of her local community and to cultivate a sense of belonging and trust, and the other by a disposition on the other student’s part to establish “boundaries” in her interaction with colleagues and to attain a “balcony view” of the turbulent events in the wider organisation. Metaphors used by the students in their writing indicated transformation of students’ habitus on their trajectories through the organisational fields

Metallosupramolecular assemblies : development of novel cyclometalated Pt(II) and Ir(III)-based capsules

Inspired by nature’s use of self-assembled systems to carry out virtually all biological processes, chemists have taken to building simplified synthetic systems that mimic the biotic world. Although transition metal-ligand interactions are rarely used for the purpose of biological self-assembly, they have several advantages over other weak noncovalent interactions, such as pronounced directionality and significant strength. These particular attributes have allowed chemists to construct a comprehensive library of self-assembled polygons and polyhedra, using different transition metal-ligand motifs. Many of these supramolecular assemblies possess cavities of defined shape and size, which are able to accommodate guest molecules. It has further been realised that isolation of guest species from the bulk phase can lead to many interesting functions, such as containment, sensing and catalysis. Herein, a new self-assembly strategy has been used to construct novel cyclometalated Pt cages and assembly of the first known [Ir(ppy)2]-based capsule has also been achieved. Chapter 1 includes an introduction to metallosupramolecular assemblies, followed by a comprehensive review of three-dimensional architectures with accessible cavities, their synthetic strategies and applications. Chapter 2 reports on the construction of novel Pt(II)-based trigonal prisms using an unusual, kinetically controlled protocol. By exploiting asymmetric cyclometalated 2-phenylatopyridine based platinum corner units that possess both labile and non-labile cis-coordination sites, trigonal prismatic stereoisomeric architectures have been selectively prepared by altering the sequence of addition of ditopic 4,4′-bipy (4,4′-bipyridine) and tritopic tpt (2,4,6-tris(4-pyridyl)-1,3,5-triazine) molecular structural components using a template free method. Collision-induced-dissociation mass spectrometry experiments were used to differentiate between the structural isomers due to their significantly different fragmentation profiles. Chapter 3 describes the synthesis and characterisation of the first molecular capsule based on an [Ir(ppy)2]+ 90° metallosupramolecular acceptor unit. Initial work focused on pyridine-based donor ligands from which an Ir2L2 metallamacrocycle was assembled. However, when the highly conjugated tpt “panels” were used, due to postulated constraints in the dihedral angle, self-assembly of the Ir6tpt4 octahedral was unsuccessful. The constraints in the dihedral angle were eliminated by swapping pyridine for nitrile-based ligands and following the development of a method to resolve rac-[(Ir(ppy)2Cl)2] into its enantiopure forms, homochiral Ir6tcb4 (tcb = 1,3,5-tricyanobenzene) octahedral capsules where realised. Photophysical studies on the Ircapsules have shown that the ensemble of cooperative, weakly coordinating ligands can lead to luminescence not present in the comparative mononuclear analogues. X-ray crystallographic analysis revealed that the Ir capsules possess cavities large enough to accommodate 4 triflate counterions. Through a series of titration experiments the ability of the capsules to act as anion sensors was also exposed. Further exploration into the host-guest chemistry of the Ir6tcb4 capsule is reported in Chapter 4. Subsequent experiments have shown that self-assembly is highly dependent on the counterions associated with the system. While a number of different anions (OTf-, BF4 -, ClO4 -, PF6 -) facilitate the formation of the same octahedral scaffold, when triflimide was employed as a bulkier counterion, no capsule was observed. On subsequent addition of smaller counterions, such as triflate, the same Ir6tcb4 cage assembles, demonstrating that the anions also act as templates. Kinetic stability experiments, undertook by monitoring the rate of scrambling of the Δ and Λ-[Ir(ppy)2]+ components within the preformed ensembles, show that the Ir capsules are up to 1.4×104 times more stable than their mononuclear analogues. The counter anions were also observed to play a crucial role in the capsule’s stability with measured scrambling half-lives ranging from 4.7 mins with tetrafluoroborate to as long as 4.5 days with triflate. In contrast, the rate of ligand exchange in simple mononuclear complexes, as ascertained using EXSY NMR experiments, was found to be approximately independent of the associated anion

Photoinduced energy- and electron-transfer from a photoactive coordination cage to bound guests.

In a coordination cage which contains an array of twelve naphthyl chromophores surrounding a central cavity, photoinduced energy or electron-transfer can occur from the chromophore array to the bound guest in supramolecular host/guest complexes

Stepwise synthesis of mixed-metal assemblies using pre-formed Ru( ii ) ‘complex ligands’ as building blocks

Two families of heteronuclear coordination complexes have been prepared in a stepwise manner using pre-formed, kinetically inert [RuL3]2+ building blocks, in which L is a bis-bidentate bridging ligand with two pyrazole–pyridyl termini, coordinated at one end to the Ru(II) centre. These pre-formed ‘complex ligands’ – with three pendant binding sites – react with additional labile transition metal dications to complete the stepwise assembly of mixed-metal arrays in which labile [Co(II)/Cd(II)] or inert [Ru(II)] ions strictly alternate around the framework. When L = the thiophene-2,5-diyl spaced ligand Lth, the complex [Ru(Lth)3]2+ is formed in the expected 3[thin space (1/6-em)]:[thin space (1/6-em)]1 mer[thin space (1/6-em)]:[thin space (1/6-em)]fac ratio: reaction with labile Co(II) or Cd(II) ions completes formation of a heteronuclear square [Ru2Co2(Lth)6]8+ or one-dimensional coordination polymer {[CdRu(Lth)3]4+}∞, respectively. In these only the mer isomer of [Ru(Lth)3]2+ is selected by the self-assembly process, whereas the fac isomer is not used. When L = a 1,3-benzene-diyl spaced ligand (Lph), the complex ligand [Ru(Lph)3]2+ formed in the initial step is enriched in mer isomer (80–87% mer, depending on reaction conditions). Two quite different products were isolated from reaction of [Ru(Lph)3]2+ with Co(II) depending on the conditions. These are the rectangular, hexanuclear ‘open-book’ array [Ru3Co3(Lph)9]12+ which contains a 2[thin space (1/6-em)]:[thin space (1/6-em)]1 proportion of fac/mer Ru(II) metal centres; and the octanuclear cubic [Ru4Co4(Lph)12{Na(BF4)4}]13+ cage which is a new structural type containing all mer Ru(II) vertices and all fac Co(II) vertices. The cavity of this cubic cage contains a tetrahedral array of fluoroborate anions which in turn coordinate to a central Na(I) ion – an unusual example of a metal complex [Na(BF4)4]3− acting as the guest inside the cage-like metal complex [Ru4Co4(Lph)12]16+

Polymeric hole-transport materials with side-chain redox-active groups for perovskite solar cells with good reproducibility

Two monomers, M:OO and M:ON, and their corresponding polymers, P:OO and P:ON, were prepared from styrene derivatives N,N-diphenyl-4-vinyl-aniline with different substitutents (-OCH3 and –N(CH3)2) in the N-phenyl para positions. The polymers were synthesised and fully characterised to study their function as hole transport materials (HTMs) in perovskite solar cells (PSCs). The thermal, optical and electrochemical properties and performance of these monomers and polymers as HTMs in PSCs were compared in terms of their structure. The polymers form more stable amorphous glassy states and showed higher thermal stability than the monomers. The different substituent in the para position influenced the highest occupied molecular orbital (HOMO) level, altering the oxidation potential. Both monomers and polymers were employed as HTMs in perovskite solar cells with a device configuration FTO/bl-TiO2/mp-TiO2/CH3NH3PbI3/HTM/Au resulting in power conversion efficiencies of 7.48% for M:OO, 5.14% for P:OO, 5.28% for P:ON and 3.52% for M:ON. Although showing comparatively low efficiencies, the polymers showed much superior reproducibility in comparison with Spiro-OMeTAD or the monomers, suggesting further optimisation of polymeric HTMs with redox side groups is warranted

Thermally Activated Delayed Fluorescence (TADF) and Enhancing Photoluminescence Quantum Yields of [Cu^I(diimine)(diphosphine)]⁺ Complexes—Photophysical, Structural, and Computational Studies

The complexes [Cu(I)(POP)(dmbpy)][BF4] (1) and [Cu(I)(POP)(tmbpy)][BF4] (2) (dmbpy = 4,4'-dimethyl-2,2'-bipyridyl; tmbpy = 4,4',6,6'-tetramethyl-2,2'-bipyridyl; POP = bis[2-(diphenylphosphino)-phenyl]ether) have been studied in a wide temperature range by steady-state and time-resolved emission spectroscopy in fluid solution, frozen solution, and as solid powders. Emission quantum yields of up to 74% were observed for 2 in a rigid matrix (powder), substantially higher than for 1 of around 9% under the same conditions. Importantly, it was found that the emission of 2 at ambient temperature represents a thermally activated delayed fluorescence (TADF) which renders the compound to be a good candidate for singlet harvesting in OLEDs. The role of steric constraints within the complexes, in particular their influences on the emission quantum yields, were investigated by hybrid-DFT calculations for the excited triplet state of 1 and 2 while manipulating the torsion angle between the bipyridyl and POP ligands. Both complexes showed similar flexibility within a +/- 10 degrees range of the torsion angle; however, 2 appeared limited to this range, whereas 1 could be further twisted with little energy demand. It is concluded that a restricted flexibility leads to a reduction of nonradiative deactivation and thus an increase of emission quantum yield

Luminescent Polymer Films from Simple Processing of Coronene and Europium Precursors in Water

We describe the preparation and optical characterisation of a coronene tetracarboxylate salt (CS) in polyvinyl alcohol (PVA) thin film solutions processed from water, neat or mixed with varying ratios of a europium tris(hexafluoroacetylacetoanto) diaquo complex [Eu(hfac)3(H2O)2]. Neat CS-PVA showed not only well-defined fluorescence peaks but also a long-lived phosphorescence emission, persisting for more than 1 second. Interaction between the CS and EuIII molecules, mediated by means of carboxylate coordination to the EuIII, was attained by simple incorporation into the PVA polymer matrix and resulted in energy transfer from the coronone antenna to the europium centre. Under various blend ratios of CS and the EuIII complex, total photoluminescence quantum yields of typically around 30 % were achieved. The straightforward processing of this type of self-assembled chromophore-lanthanide system into a luminescent polymer film offers potential for application to other chromophores, lanthanides and polymers