Design and development of novel self-assembled luminescent lanthanide complexes in solution and in soft materials

This thesis describes the design, synthesis and characterisation of naphthyl-dipicolylamide (naphthyl-dpa) ligands for sensitisation of lanthanide, Ln(III), emission. Chapter 1 provides an introduction to the fundamental physical and chemical properties of LnIII ions with particular focus on the photophysical properties. The features of emissive Ln(III) ions will be reviewed, an overview given to the mechanisms available to access this f-metal-centred luminescence and the key design features for ligands highlighted. This is followed by a review of current literature and the immediate prior art from the Gunnlaugsson laboratory. Chapter 2 will describe the design and synthesis of naphthyl-dpa derivatives functionalised with sulfonate groups, ensuring aqueous solubility of these ligands. A pair of enantiomeric ligands will be presented, the photophysical properties of these ligands and their complexes with Eu(III) are probed in both aqueous and organic solutions, showing total quantum yield enhancements in the aqueous environment. The self-assembly behaviours of the ligands is investigated using spectroscopy. Chiral spectroscopy is exploited to analyse the photophysical properties and self-assembly in greater depth and global stability constants determined by non-linear regression analysis.This chapter concludes in the formation of gelled soft matter at higher concentration, using insights from dynamic light scattering (DLS), isothermal titration calorimetry (ITC) and scanning electron microscopy (SEM). In Chapter 3, the extension of the naphthyl-dpa scaffold into responsive luminescent probes will be investigated. A family of chiral ligands and their complexes with Eu(III) are characterised in acetonitrile and methanol. The influence of the ligand substitution pattern and peripheral covalent structure is probed, revealing ?spectral fingerprints? and responsive behaviours in ligand- and metal-centred emissions. Self-assembly processes are probed in, showing similar processes between ligands, however differing significantly in their emission properties during self-assembly. A PET response is exploited in the development of acidity probes and one complex is calibrated in 5% methanol:water as a pH probe, showing a sensitive pH response in both ligand- and metal-centred emissions. This chapter concludes by describing the fabrication of a hydrogel-based pH sensor using Eu(III)-centred luminescence, clear spectroscopic and visual responses are demonstrated to both solution and vapour stimuli. Chapter 4 focusses on the design of molecular logic gate mimics (MLGMs) in solution and polymer gels. This example represents one of the first soft materials-based MLGMs using Ln(III) luminescence. Firstly, a brief introduction will present the fundamentals of logical analysis and the limited examples of exploiting Ln(III) luminescence. A mixed Eu(III):Tb(III) system will be discussed showing luminescence responses to H+ and F-. These responses are characterised in methanol and organogels parameterised as logic functions; both clear logical and visual outputs are demonstrated to unambiguously identify input states. Chapter 5 details the preliminary studies undertaken towards the covalent grafting of naphthyl-dpa binding sites to a bulk polymer chain and introduction of EuIII-based supramolecular crosslinks. Two naphthyl-dpa ligands with pendent methacrylamide moieties, and their Eu(III) complexes, are synthesised. The photophysical properties characterised spectroscopically. The self-assembly processes are characterised and particular attention is made to the luminescence lifetime distributions in a range of other solvents. Copolymers with p(HEMA-co-EGMDA) are synthesised and characterised thermally from which luminescent hydrogels are demonstrated. The emission properties characterised to elucidate the nature of the crosslinking complexes. The chapter concludes by presenting the preliminary mechanical analysis, showing inconclusive results; approaches to address, extend and exploit these preliminary results are presented. Finally, Chapter 6 outlines experimental details as well as compound characterisation. This is followed by literature references and Appendices containing relevant supplemental experimental data to that presented herein

Lanthanide luminescent logic gate mimics in soft matter: [H(+)] and [F(-)] dual-input device in a polymer gel with potential for selective component release

Non-covalent incorporation of responsive luminescent lanthanide into a polymer gel produces three-output logic circuit with significant naked-eye colour changes.</p

Quantifying the formation of chiral luminescent lanthanide assemblies in an aqueous medium through chiroptical spectroscopy and generation of luminescent hydrogels

Herein we present the synthesis and the photophysical evaluation of water-soluble chiral ligands (2·(R,R) and 2·(S,S)) and their application in the formation of lanthanide directed self-assembled structures. These pyridine-2,6-dicarboxylic amide based ligands, possessing two naphthalene moieties as sensitising antennae, that can be used to populate the excited state of lanthanide ions, were structurally modified using 3-propanesultone and caesium carbonate, allowing for the incorporation of a water-solubilising sulfonate motif. We show, using microwave synthesis, that Eu(III) forms chiral complexes in 1 : 3 (M : L) stoichiometries (Eu·[2·(R,R)]3 and Eu·[2·(S,S)]3) with these ligands, and that the red Eu(III)-centred emission arising from these complexes has quantum yields (Φtot) of 12% in water. Both circular dichroism (CD) and circular polarised luminescence (CPL) analysis show that the complexes are chiral; giving rise to characteristic CD and CPL signatures for both the Λ and the Δ complexes, which both possess characteristic luminescence dissymmetry factors (glum), describing the structure in solution. The self-assembly process was also monitored in situ by observing the changes in the ligand absorption and fluorescence emission, as well as in the Eu(III) luminescence. The change, fitted using non-linear regression analysis, demonstrated high binding affinity for Eu(III) which in part can be assigned to being driven by additional hydrophobic effects. Moreover, using CD spectroscopy, the changes in the chiroptical properties of both (2·(R,R) and 2·(S,S)) were monitored in real time. Fitting the changes in the CD spectra allowed for the step-wise binding constants to be determined for these assemblies; these matched well with those determined from both the ground and the excited state changes. Both the ligands and the Eu(III) complexes were then used in the formation of hydrogels; the Eu(III)-metallogels were luminescent to the naked-eye

Luminescent lanthanide cyclen-based enzymatic assay capable of diagnosing the onset of catheter-associated urinary tract infections both in solution and within polymeric hydrogels

Herein we present a supramolecular (delayed luminescent) Eu­(III)-based pH-responsive probe/sensor with the ability to detect the urease-mediated hydrolysis of urea in aqueous solution. A series of photophysical titrations show this Eu­(III) chelate behaves as an “<i>on–off</i>” luminescent switching probe, with its luminescence being quenched upon urea being enzymatically converted into ammonia and carbon dioxide. Calculation of the rate constant (<i>k</i>) and activation energy (<i>E</i>_a) for this hydrolysis reaction are detailed; the results demonstrate a direct observation of enzymatic activity in solution by the sensor. The potential application of this probe in detecting the onset of catheter-associated urinary tract infections (CAUTIs) is also demonstrated by incorporating <b>1.Eu</b> into water-permeable hydrogels that can be utilized as an alternative coating for catheters

Towards “drug-like” indole-based transmembrane anion transporters

A series of mono-ureas and mono-thioureas, some incorporating a trifluoromethyl group, have been synthesised and their ability to facilitate ion transport assessed using a combination of ion selective electrode and fluorescence techniques. Chloride/nitrate and chloride/bicarbonate antiport and HCl symport processes were examined using phospholipid vesicles as a model system. In general, the trifluoromethyl functionalised receptors showed greater transport activity than unfluorinated analogous systems, corresponding with increased clogP. The most active transporter facilitated chloride efflux from phospholipid vesicles at receptor to lipid ratios as low as 1:20,000. In addition, in vitro fluorescence and viability assays indicated that the most potent anion transporters induced apoptosis in human cancer cell lines.<br/