Impact of the terminal end-group on the electrical conductance in alkane linear chains

Abstract

This research presents comprehensive theoretical investigations of a series of alkane-based chains using four different terminal end groups including amine –NH₂, thiomethyl –SMe, thiol –SH and direct carbon contact –C. It is widely known that the electrical conductance of single molecules can be tuned and boosted by chemically varying their terminal groups to metal electrodes. Here, we demonstrate how different terminal groups affect alkane molecules' electrical conductance. In general, alkane chain conductance decreases exponentially with length, regardless of the anchor group types. In these simulations the molecular length varies from 3 to 8 –CH₂ units, with 4 different linker groups; these simulations suggest that the conductances follow the order G_C > G_SH > G_SMe > G_NH2. The DFT prediction order of the 4 anchors is well supported by STM measurements. This work demonstrates an excellent correlation between our simulations and experimental measurements, namely: the percent difference ΔG, exponential decay slopes, A constants and β factors at different molecular alkane chain lengths.