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Pathway Complexity in Supramolecular Porphyrin Self-Assembly at an Immiscible Liquid|Liquid Interface

submitted on 05.03.2021, 13:11 and posted on 08.03.2021, 05:33 by Iván Robayo-Molina, Andrés F. Molina-Osorio, Luke Guinane, Syed A.M. Tofail, Micheal D. Scanlon

Nanostructures that are inaccessible through spontaneous thermodynamic processes may be formed by supramolecular self-assembly under kinetic control. In the past decade, the dynamics of pathway complexity in self-assembly have been elucidated through kinetic models based on aggregate growth by sequential monomer association and dissociation. Immiscible liquid|liquid interfaces are an attractive platform to develop well-ordered self-assembled nanostructures, unattainable in bulk solution, due to the templating interaction of the interface with adsorbed molecules. Here, we report time-resolved in situ UV/vis spectroscopic observations of the self-assembly of zinc(II) meso-tetrakis(4-carboxyphenyl)porphyrin (ZnTPPc) at an immiscible aqueous|organic interface. We show that the kinetically favoured metastable J-type nanostructures form quickly, but then transform into stable thermodynamically favoured H-type nanostructures. Numerical modelling revealed two parallel and competing cooperative pathways leading to the different porphyrin nanostructures. These insights demonstrate that pathway complexity is not unique to self-assembly processes in bulk solution, and equally valid for interfacial self-assembly. Subsequently, the interfacial electrostatic environment was tuned using a kosmotropic anion (citrate) in order to control the influence the pathway selection. At high concentrations, interfacial nanostructure formation was forced completely down the kinetically favoured pathway and only J-type nanostructures were obtained. Furthermore, we found by atomic force microscopy (AFM) and scanning electron microscopy (SEM) that the J- and H-type nanostructures obtained at low and high citric acid concentrations, respectively, are morphologically distinct, which illustrates the pathway-dependent material properties.


Science Foundation Ireland (SFI) Grant no. 13/SIRG/2137

European Research Council (ERC) Starting Grant (Agreement no. 716792)

Irish Research Council’s (IRC's) Enterprise Partnership Scheme under the project ID: EBPPG/2016/271


Email Address of Submitting Author


University of Limerick



ORCID For Submitting Author


Declaration of Conflict of Interest

The authors declare no competing financial interest.

Version Notes

Manuscript is currently submitted to a journal for peer-review.