Two-Dimensional Assembly of Functional Organic Molecular Networks

Two-dimensional nanomaterials—such as graphene and its composites—hold enormous potential for use in advanced electronics, energy, separation, and even lubrication materials applications. However, small covalent changes to the relatively simple chemical composition of these carbon nanomaterials can cause rather large effects on their properties, thus making it difficult to rationally design them for target applications. Materials derived from supramolecular self-assembly processes have the potential to overcome the drawback by taking advantage of simpler-to-design molecular components that can organise themselves into complex nanostructures via favourable non-covalent intermolecular interactions such as hydrogen and halogen bonding. As a spontaneous equilibrium process, self-assembly of the molecular components proceeds via an initial nucleation event that is followed by growth to form an ordered nanostructure that represents minimum free-energy state of the system. By carrying out these thermodynamically-controlled processes on a surface, we can gain access to well-defined two-dimensional, nanometres-thick architectures whose morphology (e.g., surface pattern and architecture), density and/or porosity, and inherent functional properties arise from the precise configuration and non-covalent interactions of its constituent molecules.

Initially, building blocks will be based on aromatic lactim–lactam bonding motifs that are easily accessed in a few synthetic steps using straightforward organic chemistries and purification procedures. Aromatic lactim–lactam derivatives are known to possess luminescent properties in solution and upon aggregation; they also have the potential to reversibly store and release multiple electrons, which encourages their use as functional chemical sensors and active materials for optoelectronic and energy applications. The PhD student will exploit the highly directional hydrogen bonding interactions of self-complementary aromatic lactim–lactam units to assemble these electronically-active molecular building blocks into nanoscopically thin two-dimensional networks on conductive surfaces (e.g., Cu, Au and/or graphene). Using synthetic chemistry, the PhD student will vary the size, shape and number of hydrogen bonding sites present in these molecules to gain a better understanding of how their structural design affects the packing morphology, density and porosity of the resulting two-dimensional material in a systematic manner. They will assess fundamental self-assembly mechanisms on surfaces and probe two-dimensional network structures using a variety of advanced spectroscopies, X-ray diffraction, and materials imaging analyses. Solid-state electrochemical and conductivity measurements will be carried out on single crystals and as-prepared films to assess the effectiveness of densely-packed hydrogen bonds to transfer electrons through-space, i.e., across the self-assembled layers, to afford high conductivity. π-Electronic interactions between the aromatic centres of multi-layered films and at the substrate–nanofilm interface will also be investigated in the context of high surface conductivity. The work carried out during this project will contribute to research efforts in the rapidly growing field of low-/two-dimensional materials, which has included advances in metal coordination polymers, covalent organic frameworks (COFs) and supramolecular polymers.

Goals: to (i) develop a deeper understanding of how intermolecular interactions of functional molecules on surfaces can influence the electronic properties of a two-dimensional ensemble in order to (ii) rationally design better materials with predictable properties, i.e., for advanced energy, tribology and separations applications. Initially, the student will investigate the electronic structure–property relationship of non-porous two-dimensional materials possessing a highly dense network of hydrogen bonds. Such graphene-mimetic materials may exhibit properties suitable for implementing them as high-mobility conductive films, modified electrodes for energy storage devices and lubricating layers for tribology applications. As our fundamental understanding of these systems grows, you will then move on to investigate the structure–property relationships of two-dimensional self-assemblies that incorporate well-defined pores and edge defects into the two-dimensional nanostructure. The straightforward organic synthetic methods we will use to these materials means that the structure and porosity of two-dimensionally assembled molecule networks can be systematically investigated and their properties tuned for desired applications. In particular, porous conductive networks are gaining attention in the research communities nowadays for their high-utility potential to address challenges in active mass transport, advanced separations and high-rate/high-energy density organic rechargeable batteries.

You will fundertake cohort-based training to support development of scientific, transferable and employability skills.

You will receive training in:
– multi-step organic synthesis and standard purification techniques
– theoretical background in molecular recognition and non-covalent interactions
– solution- and solid-state NMR spectroscopy, FTIR and optical spectroscopy
– X-ray crystallography and X-ray photoelectron spectroscopy
– surface imaging and morphology analysis of organic thin films

You will become well-versed in the use of supplementary software for research planning/management, data processing and analysis.

This PhD will formally start on 1 October 2019. Induction activities will start on 30 September.