Modulated charge transport and device functionality in dual-state molecular junctions

Dual-state molecular junctions, with two coupled electronic states in charge transport, showcase a wider range of electrical functionalities in comparison to single-state junctions, attributed to the extra electronic state and the interstate coupling. We carried out a theoretical modeling investigation of charge transport and functionalities of the dual-state junction under the Landauer formula and Marcus theory frameworks. We uncovered a negative differential resistance (NDR) unique to dual-state molecular junctions, which can be fine-tuned by adjusting the polarization and coupling strength between the two electronic states in model molecules with different linking lengths and positions of the electroactive groups. Moreover, using ab initio computation via the density functional theory plus nonequilibrium Green's function method, we demonstrate controlled NDR switching with a photoresponsive chemical bridge to control interstate coupling. Combining the electronic structure analysis based on charge decomposition and the interaction diagram, our study provides valuable insights into the fundamental structure-function relationship of dual-state molecular junctions and elucidates the principles for rational molecular design of controllable NDR functionalities.