Single‐Molecule Conductance Studies of Organometallic Complexes Bearing 3‐Thienyl Contacting Groups

Abstract

The compounds and complexes 1,4‐C6H4(C≡C‐cyclo‐3‐C4H3S)2 (2), trans‐[Pt(C≡C‐cyclo‐3‐C4H3S)2(PEt3)2] (3), trans‐[Ru(C≡C‐cyclo‐3‐C4H3S)2(dppe)2] (4; dppe=1,2‐bis(diphenylphosphino)ethane) and trans‐[Ru(C≡C‐cyclo‐3‐C4H3S)2{P(OEt)3}4] (5) featuring the 3‐thienyl moiety as a surface contacting group for gold electrodes have been prepared, crystallographically characterised in the case of 3–5 and studied in metal|molecule|metal junctions by using both scanning tunnelling microscope break‐junction (STM‐BJ) and STM‐I(s) methods (measuring the tunnelling current (I) as a function of distance (s)). The compounds exhibit similar conductance profiles, with a low conductance feature being more readily identified by STM‐I(s) methods, and a higher feature by the STM‐BJ method. The lower conductance feature was further characterised by analysis using an unsupervised, automated multi‐parameter vector classification (MPVC) of the conductance traces. The combination of similarly structured HOMOs and non‐resonant tunnelling mechanism accounts for the remarkably similar conductance values across the chemically distinct members of the family 2–5.

Syntheses and molecular structures of trans-bis(alkynyl) tetrakis-triethylphosphite ruthenium complexes

“…[21,33,34] In seeking to optimise the performance of metal complex molecular wires based on trans-M(C≡CR) 2 L n frameworks, attention has been drawn to the role that the ancillary ligands L might play on tuning alignment of the critical molecular orbitals with the electrode Fermi levels. [35] Recently, both the Akita group [36] and our own [37] have been attracted to the potential that trialkylphosphite ligands might play as ancillary groups in such structures. The majority of synthetic routes to trans-bis ( δ 132.3 ppm), [42] being observed ( Figure S1).…”

Inside Back Cover: Hemilabile Ligands as Mechanosensitive Electrode Contacts for Molecular Electronics (Angew. Chem. Int. Ed. 46/2019)

“…Thiophenes are known to interact with Au electrodes and have been successfully used as molecular termini in several single-entity electronics studies. [22][23][24][25][26][27][28] Thei nteraction is reported as being weaker than traditional contact groups, [29] consistent with the known coordination chemistry of thiophenes [30][31][32] and their established use in hemilabile ligand design, [33][34][35] thus making them an ideal "supporting" molecular contact to the stronger methyl thioether. Furthermore, there are reports in the literature of unusual properties of oligothiophene-based molecular wires,s howing non-monotonic conductance attenuation with length, [36][37][38] stretchinginduced conductance decrease, [38] and large spread of conductance values [39] (see the Supporting Information for further details).…”

Nanofabrication Techniques in Large-Area Molecular Electronic Devices

“…Intense work in the field for more than four decades has included the development of methodologies based on scanning tunneling microscopy (STM) or conducting atomic force microscopy (c-afm) for measuring the electrical properties of single-molecules and molecular assemblies [14,[16][17][18][19][20][21][22]. These studies have resulted in a growing understanding of the key parameters that determine the electrical properties of molecular junctions (molecular backbone [12,23], chemical anchoring groups [24][25][26], conformation [27], metal complexation [28], redox state [18,[29][30][31], electrode material [32][33][34][35], and if applicable, the characteristics of the medium: Solvent [36], pH [37], etc. ), as well as the mechanisms behind electronic transport in molecular junctions [38][39][40].…”

“…(i) Coupling of the molecule to the electrode surface through the contacting group, which plays a crucial role and has prompted an extensive search for chemical groups that can effectively serve as molecular 'anchor groups' [25,28,35,[74][75][76][77][78]; (ii) Mechanical stability of the electrode molecular junction avoiding fluxional bonds [79,80].…”