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Single Molecule Junctions With Non-Conventional Architectures, Crafted In Silico

Periodic Reporting for period 1 - SMJCY (Single Molecule Junctions With Non-Conventional Architectures, Crafted In Silico)

Reporting period: 2016-11-01 to 2018-10-31

Unimolecular electronics is a cutting-edge field of materials research. It employs the ability of an organic molecule to sustain electric current when bridging a nanogap between the conducting leads. Such architecture is found in the scanning tunneling microscopy and atomic force microscopy, used to study the intricate details of molecular structure, and holds promise as a component of miniature electronic devices with target properties. While state-of-the-art experimental techniques have been developed to manufacture and characterize the single molecule junctions (SMJs), empirical trial-and-error approach, predominant in this field so far, struggles to address some of the common shortcomings and deduce the design principles for future devices. In this proposal, fundamental physical-organic chemistry concepts and high-level computational chemistry methods are employed to overcome this obstacle and further this fascinating area of research. Various non-conventional candidate architectures are developed to achieve improved performance and broaden the functionality of the SMJs. Both common and in-house computational chemistry tools are used to identify molecular-level performance descriptors and deduce the relevant structure-function relationships. The key objectives of this project are to offer guidance for the mix-and-match design of future experiments and yield new and improved SMJ architectures.
Several molecular junction types have been studied in silico so as to identify the key descriptors connecting molecular structure with the junction conductance and develop more conductive systems. 1) For thiophene-based wires with tunable charge carrier type, we have analyzed the molecular orbital factors affecting their conductance and devised a simple in silico tool for predicting the carrier type change based on the charge transfer trends. 2) In the context of through-space transport, we have investigated diverse π-stacked dimers, pertinent both to molecular junctions and semiconductors. We have illustrated that the same chemical concepts define their performance in these two very different types of electronic assemblies. These concepts were employed to design more conductive junctions. 3) Moving beyond conventional π-conjugated systems, we have studied molecular junctions featuring fully saturated hydrocarbons. For various carbon nanothreads, we have illustrated that their conductance is driven by their complex topology. The latter was utilized to develop new multidimensional nanothreads with unprecedented for systems lacking π-conjugation zero-bias transmission probabilities. We have also demonstrated that hydrocarbons with various σ-aromaticity patterns display diverse conductance behavior, particularly outstanding in the case of σ-antiaromatic cores. These results have been reported in high-impact peer-reviewed journals (e.g. Journal of Physical Chemistry Letters, Journal of the American Chemical Society, etc.), cited by other scientists, reported to diverse audiences via scientific meetings (including oral presentations at the International Workshop on “Molecular-Scale Electronics: Concepts, Contacts, and Stability” in UK in 2017, ValBO ICQC satellite meeting on Understanding Chemistry and Biochemistry with Conceptual Models in France, 54th Symposium on Theoretical Chemistry “Non-Covalent Interactions” in Germany and 9th International Conference on Molecular Electronics in France in 2018) and outreach activities (e.g. the MSCA Falling Walls Lab and the Lindau Nobel Meeting in 2017).
Fundamentally new physical-organic chemistry insights into the properties of organic electronic assemblies have been established and used to 1) develop a new diagnostic for the charge carrier tuning, design new functional architectures exploiting 2) π-stacking in the dimer assemblies and 3) topology and 4) σ-aromaticity in the fully saturated systems. These findings are likely to impact the future research in the area of unimolecular electronic as they offer new design guidelines and concepts. While the direct socio-economic impact and wider societal implications of this theoretical research are hard to quantify, it is our hope that they expand the fundamental understanding of electronic transport in organic molecules and inspire the future experimental effort.