(Invited) Chemistry in a Nanoscale Gap

Abstract

In the realm of the Single-Molecule Electronics, a suite of advanced electrical characterization approaches have emerged allowing measuring charge transport in an electric contact made out of an individual molecule[1]. The field has (and is still) drawn(ing) an scenario where individual molecules can be chemically modified to deliver a particular electrical function in a nanoscale circuit, e.g. variable resistors[2], diodes[3], switches[4], etc. Along this excursion, we have observed that single molecules trapped in a nanoscale tunneling junction experience conformational structural changes and changes in molecule/electrode contact geometries, which are usually accompanied by large conductance variations and can be easily detected electrically[1]. Such changes are induced by the imposed forces fields experienced by the molecules within the nanoscale gap, namely, a mechanical force and/or an electric field. In the past decade, we have learnt that under certain force field conditions, the individual molecules wired in a nanoscale junction undergo chemical transformations. Here, we will present a couple of illustrative examples of the use of single-molecule junction to study and control reactivity at the nanoscale using electric fields, a concept that is inherent in the natural enzymatic molecular machinery[5]. Tunable, well-oriented electric fields can be easily delivered along the main junction axis of a nanoscale electrical device[6]. We exploited the latter to study; (1) a simple monomolecular cis-trans isomerization reaction[7], and (2) a bi-molecular Diels-Alder reaction[8]. Along with the experimental design and fundamental chemistry aspects, we will discuss the advantages these examples can bring to possible technological applications.[1]. L. Sun et al. Chem. Soc. Rev., 2014,43, 7378-7411.[2]. A. C. Aragones et al. Chem. Eur.J.2015, 21,7716 –7720.[3]. I. Diez-Perez et al. Nature Chemistry 1, 635–641 (2009).[4]. N. Darwish et al. Nano Lett. 2014, 14, 12, 7064–7070.[5]. Stephen D. Fried et al. Annu Rev Biochem. 2017; 86: 387–415.[6]. N. Darwish et al. “Principles of Molecular Devices Operated by Electric Fields” in Effects of Electric Fields on Structure and Reactivity: New Horizons in Chemistry, Royal Society of Chemistry, Ed. Sason Shaik.[7]. C. S. Quintans et al. Appl. Sci. 2021, 11(8), 3317.[8]. A. C. Aragones et al. Nature 531, 88–91 (2016).