Robust Organic Radical Molecular Junctions Using Acetylene Terminated Groups for C–Au Bond Formation

Abstract

Organic paramagnetic and electroactive molecules are attracting interest as core components of molecular electronic and spintronic devices. Currently, further progress is hindered by the modest stability and reproducibility of the molecule/electrode contact. We report the synthesis of a persistent organic radical bearing one and two terminal alkyne groups to form Au-C σ bonds. The formation and stability of self-assembled monolayers and the electron transport through single-molecule junctions at room temperature have been studied. The combined analysis of both systems demonstrates that this linker forms a robust covalent bond with gold and a better-defined contact when compared to traditional sulfur-based linkers. Density functional theory and quantum transport calculations support the experimental observation highlighting a reduced variability of conductance values for the C-Au based junction. Our findings advance the quest for robustness and reproducibility of devices based on electroactive molecules.

Exploiting the versatile alkyne-based chemistry for expanding the applications of a stable triphenylmethyl organic radical on surfaces

“…In this work, the focus was placed on the reaction between the organic radical (2-Rad, Fig. 1), previously synthesized, 26 and an azidomethyl ferrocene (Fc-N 3 ) derivative leading to a donor-acceptor (D-A) SAM.…”

“…59 Compounds 2-Rad, 3-Rad, 2-H and 3-H were used to generate SAM-2-Rad, SAM-3-Rad, SAM-2-H and SAM-3-H, respectively. These SAMs were prepared following a similar previously reported methodology, 26 working under inert conditions to avoid the oxidation of the alkyne (see ESI † for further details on the SAM preparation). All the SAMs were characterized by different electrochemical techniques: CV, square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS).…”

“…Terminal alkynes have appeared as an appealing alternative to the thiol group as they spontaneously and covalently react with gold. 24,25 Besides the stability of the C-Au bond, the high directionality of the s-bonded C-Au has been demonstrated to provide higher conductance at the single-molecule level, 26 which makes terminal alkynes very attractive for molecular electronics. Interestingly, these functional groups can also be used to covalently react with hydrogen-terminated silicon (Si-H) surfaces.…”

Design of Perchlorotriphenylmethyl (PTM) Radical‐Based Compounds for Optoelectronic Applications: The Role of Orbital Delocalization

“…In this work, TD‐DFT has been used to examine the electronic and optical properties of the thiophene‐based PTM compounds described before. The study has been further extended to newly synthetized PTM‐based compounds, ( PTM‐Ac, Ac‐PTM‐Ac, PTM‐BTA , and BTA‐PTM‐BTA ); note that the synthesis and characterization of BTA‐PTM‐BTA has not been reported before and have been accomplished here for the sake of a detailed comparison between experimental and theoretical data. These systems exhibit one or two phenyl ring(s) connected by a vinylene bridge to the PTM radical and differ by the nature of the terminal group attached to the phenyl ring: acetylene for PTM‐Ac and bistriazene for PTM‐BTA .…”

Two-dimensional self-assembly and electrical properties of the donor-acceptor tetrathiafulvalene-polychlorotriphenylmethyl radical on graphite substrates

“…As a result, the Fermi level of the electrodes is closer to the SUMO of the radical dyad than to the LUMO of the non-radical dyad, thereby enhancing notably the charge transport by a tunneling mechanism assisted by the SUMO orbital. [35][36][37][38][39] Therefore, it is concluded that the enhancement of conductivity by the presence of radical molecules on metallic surfaces, named as "radical-conductivity enhancement" phenomenon, does not require the organization of molecules in SAMs since it can be attained with a deposition by the easy and fast drop-casting method where molecules usually adopt random orientations. It is also worth mentioning that all I-V curves obtained for S1 were slightly asymmetric, displaying small, but observable inverted rectification values with larger currents at the negative bias than at the positive ones.…”