Studies of a series of Benzene-1,3,5-derivatives and some other supramolecular building blocks and their self-assembly properties

Abstract

This thesis, titled Studies of a series of Benzene-1,3,5-derivatives and some other supramolecular building blocks and their self-assembly properties , describes the synthesis and characterisation of novel tripodal systems based on the benzene-1,3,5-tricarboxamide (BTA) motif. As will be outlined in the introduction, the ability to design, tune and control supramolecular materials formed through self assembly processes is an area of great importance and increasing interest. The introduction will provide the reader with an overview of functional supramolecular materials, the various interactions that drive their formation and their properties. Some of the most relevant advances in the literature are reviewed, with a particular focus on soft materials showing gelation. While gelation is a behaviour very well known for high molecular weight systems, such as covalent polymers, the field of low-molecular weight gelators (LMWGs), i.e. systems able to achieve gelation through networks of supramolecular interactions has gained increased attention in the last few decades and will be hereby discussed. Several tripodal systems based on the BTA motif possessing these properties will be outlined. Furthermore, the introduction will present an overview of the lanthanide metal ions, detailing their photophysical properties, their role in the formation of the metal-directed self-assemblies, supramolecular polymers etc, and finally the chapter will close describing some of the most relevant advancement to supramolecular chemistry achieved by the Gunnlaugsson group in the recent years. Chapter 2 will describe the design rationale and the synthesis of the tripodal BTA systems presented in the thesis, their purification procedures and the chemical characterisation. An alternative synthetic pathway will also be presented, and a second family of supramolecular building blocks will be shown. Chapter 3 will focus on the spectroscopic and morphologic investigations of the systems presented in the previous chapter. The interactions of the BTA ligand with the Eu(III) ions is investigated by performing titration at two different ligand concentrations; ultraviolet-visible spectroscopy as well as fluorescence is recorded and used to gain some insight on the ground and excited states of the ligands, while metal centred emission studied through phosphorescence spectroscopy. The data obtained from these titrations is processed using non linear regression analysis to determine speciation and stability constants, while proposing a mode for the formation of the self assembled species. The formation of such aggregates in solutions is then investigated including their morphology using scanning electron microscopy (SEM) of their dried solutions; furthermore, the formation of various gels is investigated using the same technique. Chapter 4 will describe a collaboration work performed with a fellow Gunnlaugsson group member in which one of the BTA systems will be used in conjunction with a Tb(III) cyclen-based complex to form a ternary system able to self assemble into a higher order aggregates. The synthesis of the ternary system, as well as the spectroscopic and morphologic characterisation is presented. Chapter 5 will present a series of aggregating systems based on two well known motifs, squaramide and 1,8-naphthalimide. The studies highlight the processes leading to their self-assembly properties and how the appropriate design influences the forces that lead to the aggregation, correlating the structures with the morphologies observed through SEM imaging. Chapter 6 contains the experimental details and will be followed by references in Chapter 7. The additional information, such as data for the work described, characterisation etc, can be found in the Appendix.