Overview of key results:
(1) The self-assembly of carboxyphenyl-substituted porphyrins into highly ordered nanostructures selectively at the interface between two immiscible liquids (Journal of Physical Chemistry C, 2020, 124, 6929). The unique physicochemical properties of the liquid-liquid interface are exploited to provide a one-step method in which the self-assembly of porphyrin molecules into crystalline nanostructures is triggered by manipulating the pH of the porphyrin aqueous solution. The photoactivity of the these free-floating porphyrin films is demonstrated in situ by illumination of the electrified liquid-liquid interface.
(2) The electrochemical analysis of the kinetics and thermodynamics of ion intercalation into solid matrices through purely ionic processes, not linked to a redox reaction. The dynamics of ion intercalation into a floating film of inorganic zinc porphyrin interfacial nanostructures are driven by electrifying an immiscible liquid-liquid interface (Journal of Physical Chemistry C, 2020, 124, 18346). Modelling using a Frumkin isotherm suggested a positive cooperativity mechanism for ion intercalation linked with structural rearrangements of the porphyrins within the nanostructures as a function of potential applied at the liquid-liquid interface.
(3) The reversible structural rearrangement of a soft porphyrin membrane under an electrical potential stimulus in the absence of solid-state architectures (Chemical Science, 2021, 12, 10227). The free-floating porphyrin membrane lies at the interface between immiscible aqueous and organic electrolyte solutions and is formed through interfacial self-assembly of zinc(II) meso-tetrakis(4-carboxyphenyl)porphyrins. In situ UV/vis absorbance and polarisation-modulated fluorescence spectroscopies in total internal reflection mode show that ionic intercalation and exchange involving the organi electrolyte cation induces a structural interconversion of the individual porphyrin molecules in the membrane from an H- to a J-type molecular configuration. These structural rearrangements are reversible over 30 potential cycles. Soft molecular assemblies that respond reversibly to external stimuli are attractive materials as on/off switches, in optoelectronic, memory and sensor technologies.
(4) The first conclusive proof that pathway complexity occurs at interfaces, in this case an interface formed between two immiscible liquids, and not just in bulk solutions (Journal of the American Chemical Society, 2021, 143, 9060). The consequences of this insight are profound since, by understanding the kinetics of the pathway complexity process, we can adjust the experimental conditions to favour one self-assembly pathway over another. This means that nanostructures with widely diverging physiochemical properties, such as their morphology, may be formed from the same initial monomers at the liquid|liquid interface. The model species studied is zinc(II) 5,10,15,20-(tetra-4-carboxyphenyl)porphyrin (ZnTPPc), a dye molecule of particular interest for solar energy conversion and storage applications. ZnTPPc has a strong absorbance in the visible range and is therefore highly amenable to UV/vis spectroscopic analysis. By combining a custom in situ UV/vis spectroscopy in total internal reflection methodology (TIR-UV/vis) methodology at the liquid-liquid interface and use of advanced chemometric tools to analyse the spectra, the complex mechanism by which self-assembly proceeds using kinetic model calculations (isodesmic and cooperative, respectively) was explained. Two parallel and competing pathways leading to the different ZnTPPc nanostructures were revealed.
(5) Electropolymerisation of thin films of free-standing conducting polymers at an electrified water-oil interface (Journal of the American Chemical Society, 2022, 144, 4853). Poly(3,4-ethylenedioxythiophene), known as PEDOT, the most commerically exploited polymer, was used as a model system. In a major breakthrough, the precise experimental conditions to electropolymerise a thin film of PEDOT were optimised using an aqueous oxidant (cerium) to oxidise the EDOT monomer exclusively at the electrified water-oil interface. This unique “direct-to-2D” method yielded PEDOT thin films with beyond-the-state-of-the-art biocompatability and outstanding conductivity.
