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.



Highly directional hydrogen bonding interactions of self-complementary hydrogen bond motifs (azoles, lactam-lactim, amide) units will be exploited to assemble redox-active molecular building blocks into nanoscopically thin two-dimensional networks on conductive surfaces (e.g., Cu, Au and/or graphene). The size, shape and number of hydrogen bonding sites present in these molecules will be modified systematically in order to gain a better understanding of how their structural design affects the packing morphology, density and porosity of the resulting two-dimensional material. Fundamental self-assembly mechanisms on surfaces and probe two-dimensional network structures will be assessed using a variety of advanced spectroscopies (X-ray photoelectron spectroscopy), powder X-ray diffraction, wide and small-angle X-ray diffraction, and high resolution scanning tunneling and electron microscopies. Solid-state voltammetry, electrochemical impedance and conductivity measurements will be carried out on single crystals and as-prepared microcrystalline thin films to assess the effectiveness of densely-packed hydrogen bonds to transfer electrons through space, i.e., laterally across the self-assembled layers, to afford high conductivity. Finally, through collaborations with Engineering groups, we will also investigate the nanotribological properties of these self-assembled hydrogen bonded surfaces, which are anticipated to provide a new paradigm for generating low friction as a result of hydration lubrication mechanisms. 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, and will be highly relevant to the interests of EPSRC Priority (Grow) Areas: Energy storage, Materials for energy applications, as well as Maintain Areas: Condensed matter (electronic structure), Electrochemical sciences, Graphene and carbon nanotechnology, Surface science, Synthetic supramolecular chemistry.