Development of a molecular toolbox for multifunctional lanthanide-based supramolecular materials : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University, Albany, New Zealand

Abstract

Using simple building blocks to develop functional supramolecular materials is an active area of research. To this extent the use of lanthanide ions (Ln³⁺ to direct supramolecular self-assembly with organic ligands has become a popularised method whereby the interesting photophysical properties of Ln³⁺ can be manipulated by simple modification of the organic architecture. Applications of such systems vary from solar waveguides, OLEDS, molecular sensors, contrast agents, bio-probes, security inks and barcodes. Herein, a synthetic strategy has been developed and investigated to readily functionalise the organic scaffolds 2,6-pyridinedicarboxamide (PDA) and 6-carbamoylpyridine-2-carboxcylic acid (PDC), using 1,2,3-triazole “click” chemistry. Using this approach, we have synthesised and assessed the f-directed self-assembly ability of some novel PDA-based and PDC-based assemblies. Initial studies focused on symmetrical incorporation of the 1,2,3-triazole linker into the PDA motif via side carbonyls. This resulted in the development of four ligand architectures (1-4), which in the presence of Eu³⁺ and Tb³⁺ self-assemble into Ln(L)₃ (CF₃SO₃)₃ (where L = 1-3) luminescent assemblies. While results of the PDA systems were promising, the systems were relatively unstable in competitive solvents, and as a result subsequent systems focused on the unsymmetrical modification of the PDC motif. Incorporation of our synthetic strategy into the PDC motif was straightforward and additionally improved both Ln³⁺ complex stability and emission intensity. Using this approach, amphiphilic ligand 5 and visibly emissive amphiphilic complexes Ln(5)₃ (where Ln = Eu³⁺, Tb³⁺, Sm³⁺ and Dy³⁺) were synthesised. The incorporation of a long alkane chain via the 1,2,3-triazole in ligand 5 allowed for the fabrication of ultra-thin luminescent films by Langmuir-Blodgett (LB) technique resulting in bright visibly emissive monolayer films. Furthermore, mixing of the emissive Ln(5)₃ complexes resulted in tunable emission dependent on the composition in both solution and monolayer film. Following this, single component dual emissive systems Ln(6)₃, [Ln(7)₃](CF₃SO₃)₃ and Ln(8)₃ were developed. This entailed the incorporation of blue emissive 1,8-naphthalimide (6 & 7) and pyrene (8) via the 1,2,3-triazole linker. When complexed with Eu³⁺ it resulted in dual emissive systems which were colour-tunable, changing colour dependent on the excitation wavelength, and in the case of Eu(6)₃ and Eu(8)₃ it results in white emissive solids and solutions. These properties were transferable to thin films, by spin coating techniques. Finally, the synthetic strategy was used in the initial development of multi-nuclear assemblies forming three multitopic ligands (9-11) and initial complexation studies were undertaken.