Amine-linked single-molecule circuits: systematic trends across molecular families

Abstract

A comprehensive review is presented of single-molecule junction conductance measurementsacross families of molecules measured while breaking a gold point contact in a solution ofmolecules with amine end groups. A theoretical framework unifies the picturefor the amine–gold link bonding and the tunnel coupling through the junctionusing density functional theory based calculations. The reproducible electricalcharacteristics and utility for many molecules is shown to result from the selective bindingbetween the gold electrodes and amine link groups through a donor–acceptorbond to undercoordinated gold atoms. While the bond energy is modest, themaximum force sustained by the junction is comparable to, but less than, thatrequired to break gold point contacts. The calculated tunnel coupling providesconductance trends for all 41 molecule measurements presented here, as well asinsight into the variability of conductance due to the conformational changeswithin molecules with torsional degrees of freedom. The calculated trends agreeto within a factor of 2 with the measured values for conductance ranging from10−7G0 to10−2G0, whereG0 is the quantumof conductance (2e2/h).