Enhanced Separation Concept (ESC): Removing the Functional Subunit from the Electrode by Molecular Design

Thomas Brandl,Marcel Mayor,Herre S J Van Der Zant,Gero D Harzmann,Riccardo Frisenda,Davide Stefani,Maria El Abbassi

doi:10.1002/ejoc.201900432

Thomas Brandl, Marcel Mayor + Show 5 more

Open Access

https://doi.org/10.1002/ejoc.201900432

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Abstract

A new concept to improve the reliability of functional single molecule junctions is presented using the E‐field triggered switching of FeIIbis‐terpyridine complexes in a mechanically controlled break junction experiment as model system. The complexes comprise a push‐pull ligand sensing the applied E‐field and the resulting distortion of the FeII ligand field is expected to trigger a spin‐crossover event reflected in a sudden jump of the transport current. By molecular engineering, the active centre of the complex is separated from the gold electrodes in order to eliminate undesired side‐effects. Two aspects are considered to isolate the central metal ion, namely the spacing by introducing additional alkynes, and the steric shielding achieved by bulky isopropyl groups. With this small series of model complexes, a pronounced correlation is observed between the occurrence of bistable junctions and the extent of separation of the central metal ion, affirming the hypothesized Enhanced Separation Concept (ESC).

Highlights

Since the visionary claim of Gordon Moore[1] predicting the ongoing miniaturization of electronic circuits to improve their performance, alternative concepts to complement metal-oxide semiconductor (CMOS) technology moved into the focus of interest
While single-molecule junctions based on scanning microscopy technologies often profit from the analytical power of the integration set-up providing structural insight into the spatial arrangement of the molecular structure inside the junction, this is not the case for junctions based on mechanically controlled break junctions (MCBJ) or electrode pairs prepared by electromigration
The second tpy-ligands of the heteroleptic complexes 1–3 are exposing an electron withdrawing group (EWG) on one side and an electron donating group (EDG) on the other side creating a dipole moment, which can align in an E-field

Summary

Introduction

Since the visionary claim of Gordon Moore[1] predicting the ongoing miniaturization of electronic circuits to improve their performance, alternative concepts to complement metal-oxide semiconductor (CMOS) technology moved into the focus of interest. We report our attempts to increase the control over the complexes arrangement in the single-molecule junction by improving the design of the immobilizing and electrode bridging tpy-ligand.

Results

Conclusion