Switchable Organic Low-Loss Spin Filters Based on Gold-Viologen-Gold Molecular Junctions

Modulating functional groups on molecules can achieve novel electron transport properties in single-molecule electronics. In this work, three organic radicals including sp2 hybridized O•, NH•, and CH2 • are attached to viologen derivatives, and their spin transport is studied by combining density functional theory and nonequilibrium Green’s function (DFT-NEGF) techniques. Excellent spin filtering efficiency (SFE) is that the α spin transport conductance is about 2 orders of magnitude larger than the β spin conductance, and this is achieved within a low-bias window. This is elucidated by the localized spin splitting of valence electrons and destructive quantum interference (DQI) of frontier molecular orbitals. Interestingly, our calculated results clearly show that both tuning the alkyl chain length and the applied bias can achieve the transformation of high and zero SFE. Our findings offer a new strategy for realizing single-molecule spin switches with viologen-based radical systems.