Synthetic Control of Quantum Interference by Regulating Charge on a Single Atom in Heteroaromatic Molecular Junctions.

Naghibi, Saman, Ismael, Ali K, Vezzoli, Andrea ORCID: 0000-0002-8059-0113, Al-Khaykanee, Mohsin K, Zheng, Xijia, Grace, Iain M, Bethell, Donald ORCID: 0000-0002-7320-7585, Higgins, Simon J ORCID: 0000-0003-3518-9061, Lambert, Colin J and Nichols, Richard J ORCID: 0000-0002-1446-8275
(2019) Synthetic Control of Quantum Interference by Regulating Charge on a Single Atom in Heteroaromatic Molecular Junctions. The journal of physical chemistry letters.

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A key area of activity in contemporary molecular electronics is the control of quantum interference (QI) in molecular junctions and devices. A range of strategies have been employed to understand and regulate QI, with features such as chemical substitution, connectivity, aromaticity and conjugation, electrochemical potential and non-covalent interactions being varied. Fused ring systems containing heteroatoms provide new opportunities for systematically exploring relationships between the structural, chemical and electronic states of a molecular wire and quantum interference, through measurement of its single-molecule electrical conductance. Here we study and modify a range of pyrrolodipyridines (carbazole-like) molecular wires. We are able to change the quantum interference patterns and hence the single-molecule conductance by chemically regulating the bridging nitrogen atom in the tricyclic ring system. A series of eight different N-substituted pyrrolodipyridines has been synthesized and subjected to single-molecule electrical characterization using an STM break junction. For meta connectivity to the electrodes a clear correlation is found between the charge residing on the pyrrolic nitrogen and the molecular conductance. This allows us to introduce a simple conceptual model which links the molecular conductance for each molecule in this series with pKa of the corresponding aniline used in the synthesis of the given compound. Correlations of these experimental data with theoretical calculations underline the importance of the pyrrolic nitrogen in facilitating conductance across the molecular bridge and controlling quantum interference. The large chemical gating for the meta connected series is not apparent for the para series, showing the competition between (i) meta connectivity quantum interference phenomena and (ii) the ability of the pyrrolic nitrogen to facilitate conductance, that can be modulated by chemical substitution. Our work demonstrates a purely synthetic method to harness and control quantum interference features, which complements existing electrochemical/electrostatic and (photo)chemical approaches.

Item Type: Article
Depositing User: Symplectic Admin
Date Deposited: 16 Oct 2019 15:38
Last Modified: 05 May 2021 16:21
DOI: 10.1021/acs.jpclett.9b02319
Open Access URL: