Seminar: The Electrical Properties of Porphyrins and Other Single Molecule Wires

ABSTRACT

We have exploited STM based methods for making single molecule measurements on a wide variety of molecular targets from short molecular bridges, to redox active organometallic molecular wires and for complex supramolecular assemblies. Such measurements have been made as two-terminal determinations and also under electrochemical potential control with electrolytes varying from aqueous solutions to ionic liquids. The lecture presents detailed measurements of the electrical properties of a variety of molecular wires with a focus on porphyrins and other more complex molecular structures. In the case of porphyrin molecular wires this lecture discusses how single molecule measurements have contributed to understanding charge flow through and the current-voltage response of porphyrin wires. This presentation will review some of our findings on the electrical properties of porphyrin molecule wires as well as presenting our latest data recorded using the STM break junction method, with a focus on mechanisms and stochastics of charge transport in porphyrin single molecule wires. Given time I will also discuss examples of our work on electrochemical switching of single molecules, with switching of single molecule radicals and also defined metal clusters discussed.  In the latter case a pyridyl-capped polyoxometalate has been used to fabricate electrochemically switchable single-molecule junctions. Using the in-situ electrochemical STM has allowed us to probe charge transport through different oxidation states of the polyoxometalate, and an efficient three-state transistor is reported on. These results show the promise of polyoxometalates in nanoelectronics and give an insight into their charge transfer and their single-molecule electrochemical behaviour.

References:

1.         Xu, W.J., et al., A Peierls Transition in Long Polymethine Molecular Wires: Evolution of Molecular Geometry and Single-Molecule Conductance. Journal of the American Chemical Society, 2021. 143(48): p. 20472-20481.

2.         Qiao, X., et al., Single-Molecule Junction Formation in Deep Eutectic Solvents with Highly Effective Gate Coupling. Journal of Physical Chemistry C 2023, 127 (26), 12802-12810, Article. DOI: 10.1021/acs.jpcc.3c03129.

3.         Sil, A., et al., Zero-Bias Anti-Ohmic Behaviour in Diradicaloid Molecular Wires. Angewandte Chemie-International Edition 2024, 63 (44), Article. DOI: 10.1002/anie.202410304.

BIOGRAPHY

Professor Nichols currently heads a research team investigating aspects of conduction in single molecules, single molecule electrochemistry, probe microscopy, nanoscale electrochemistry, interfacial electrochemistry, metal plating and in-situ spectroscopic methods for studying electrode surfaces. He is an expert in the field of scanning probe microscopy, particularly as applied to in-situ electrochemical measurements and single molecule electronics.  He has ~200 publications in peer-reviewed journals (h-index on Google Scholar = 67) and he is known internationally for pioneering in-situ electrochemical STM work. He was one of the first to carry out high-resolution studies of electrode processes, including the growth of metal electrodeposits. He received the 2003 Tajima prize from the International Society of Electrochemistry and was elected a Fellow of the International Society of Electrochemistry in 2008. He was awarded Geoffrey Barker Medal of the Royal Society of Chemistry.