Giant single-molecule conductance enhancement achieved by strengthening through-space conjugation with thienyls

Exploring single-molecule wires with high conductance is of significant importance for constructing efficient molecular electronic devices. Contrary to the general method of increasing through-bond conjugation in conventional molecular wires, strengthening through-space conjugation is proposed herein to improve molecular conductance. A series of through-space conjugated molecular wires based on hexaphenylbenzene (HPB) are synthesized, and their crystal and electronic structures, conductance behaviors, and working mechanisms are investigated. The scanning tunneling microscopy-break junction technique discloses that, by replacing phenyls with thienyls in HPB, the molecular conductance is apparently boosted, with up to ∼239-fold enhancement, and becomes larger than that of the through-bond conjugated control molecule. The flicker noise analyses and theoretical calculation confirm that improved through-space conjugation with thienyls contributes significantly to high conductance. These findings demonstrate that the introduction of strong through-space conjugation is an effective and feasible approach to attain high molecular conductance.