Visualizing the Role of Molecular Orbitals in Charge Transport through Individual Diarylethene Isomers

Diarylethene molecules are prototype molecular switches with their two isomeric forms exhibiting strikingly different conductance, while maintaining similar length. We employed low-temperature scanning tunneling microscopy (STM) to resolve the energy and the spatial extend of the molecular orbitals of the open and closed isomers when lying on a Au(111) surface. We find an intriguing difference in the extension of the respective HOMOs and a peculiar energy splitting of the formerly degenerate LUMO of the open isomer. We then lift the two isomers with the tip of the STM and measure the current through the individual molecules. By a simple analytical model of the transport, we show that the previously determined orbital characteristics are essential ingredients for the complete understanding of the transport properties. We also succeeded in switching the suspended molecules by the current, while switching the ones which are in direct contact to the surface occurs nonlocally with the help of the electric field of the tip

Charge Transport Characteristics of Diarylethene Photoswitching Single-Molecule Junctions

We report on the experimental analysis of the charge transport through single-molecule junctions of the open and closed isomers of photoswitching molecules. Sulfur-free diarylethene molecules are developed and studied via electrical and optical measurements as well as density functional theory calculations. The single-molecule conductance and the current–voltage characteristics are measured in a mechanically controlled break-junction system at low temperatures. Comparing the results with the single-level transport model, we find an unexpected behavior of the current-dominating molecular orbital upon isomerization. We show that both the side chains and end groups of the molecules are crucial to understand the charge transport mechanism of photoswitching molecular junctions