The conductance isotope effect in oligophenylene imine molecular wires depends on the number and spacing of 13C-labeled phenylene rings

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Colin-Molina, Abraham and Nematiaram, Tahereh and Man Hong Cheung, Andy and Troisi, Alessandro and Frisbie, C. Daniel (2024) The conductance isotope effect in oligophenylene imine molecular wires depends on the number and spacing of 13C-labeled phenylene rings. ACS Nano, 18 (10). pp. 7444-7454. ISSN 1936-0851 (https://doi.org/10.1021/acsnano.3c11327)

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Abstract

We report a strong and structurally sensitive 13C intramolecular conductance isotope effect (CIE) for oligophenyleneimine (OPI) molecular wires connected to Au electrodes. Wires were built from Au surfaces beginning with the formation of 4-aminothiophenol self-assembled monolayers (SAMs) followed by subsequent condensation reactions with 13C-labeled terephthalaldehyde and phenylenediamine; in these monomers the phenylene rings were either completely 13C-labeled or the naturally abundant 12C isotopologues. Alternatively, perdeuterated versions of terephthalaldehyde and phenylenediamine were employed to make 2H(D)-labeled OPI wires. For 13C-isotopologues of short OPI wires (<4 nm) in length where the charge transport mechanism is tunneling, there was no measurable effect, i.e., 13C CIE ≈ 1, where CIE is defined as the ratio of labeled and unlabeled wire resistances, i.e., CIE = R heavy/R light. However, for long OPI wires >4 nm, in which the transport mechanism is polaron hopping, a strong 13C CIE = 4-5 was observed. A much weaker inverse CIE < 1 was evident for the longest D-labeled wires. Importantly, the magnitude of the 13C CIE was sensitive to the number and spacing of 13C-labeled rings, i.e., the CIE was structurally sensitive. The structural sensitivity is intriguing because it may be employed to understand polaron hopping mechanisms and charge localization/delocalization in molecular wires. A preliminary theoretical analysis explored several possible explanations for the CIE, but so far a fully satisfactory explanation has not been identified. Nevertheless, the latest results unambiguously demonstrate structural sensitivity of the heavy atom CIE, offering directions for further utilization of this interesting effect.

ORCID iDs

Colin-Molina, Abraham, Nematiaram, Tahereh ORCID logoORCID: https://orcid.org/0000-0002-0371-4047, Man Hong Cheung, Andy, Troisi, Alessandro and Frisbie, C. Daniel;
  • Item type:Article
    ID code:88389
    Dates:
    Date
    Event
    12 March 2024
    Published
    27 February 2024
    Published Online
    15 February 2024
    Accepted
    Subjects:Science > Chemistry
    Department:Faculty of Science > Pure and Applied Chemistry
    Depositing user: Pure Administrator
    Date deposited:11 Mar 2024 14:54
    Last modified:11 Nov 2024 14:14
    URI:https://strathprints.strath.ac.uk/id/eprint/88389
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