A major goal of molecular electronics is the development and implementation of devices such as single‐molecular switches. Here, measurements are presented that show the controlled in situ switching of diarylethene molecules from their nonconductive to conductive state in contact to gold nanoelectrodes via controlled light irradiation. Both the conductance and the quantum yield for switching of these molecules are within a range making the molecules suitable for actual devices. The conductance of the molecular junctions in the opened and closed states is characterized and the molecular level E 0, which dominates the current transport in the closed state, and its level broadening Γ are identified. The obtained results show a clear light‐induced ring forming isomerization of the single‐molecule junctions. Electron withdrawing side‐groups lead to a reduction of conductance, but do not influence the efficiency of the switching mechanism. Quantum chemical calculations of the light‐induced switching processes correlate these observations with the fundamentally different low‐lying electronic states of the opened and closed forms and their comparably small modification by electron‐withdrawing substituents. This full characterization of a molecular switch operated in a molecular junction is an important step toward the development of real molecular electronics devices.

The field of molecular electronics has progressed in recent years and demonstrated functionalities such as singlemolecule switches, [1,2] field emitters, [3] and even gateable structures. [4,5] Variations of the overall conductance of all these structures in nominally identical junctions were, however, large. Differences in conductance between these junctions were identified by recording conductance histograms of all measured junctions. Large conductance variations could be demonstrated between highand low-conductance states by using quantum interference effects [5] or by changing the molecular structures in a controlled way. [6] To be able to use molecules as future components in electronic applications, it would be useful not only to have binary, high and low, conductance states available, but also a range of possible modifications to fine-tune the exact properties of the circuit. Metallorganic components lend themselves for this purpose because of the broad palette of ions, promising also a broad range of achievable conductance properties. The influence of metal ions incorporated into porphyrin molecules has already been investigated, showing a decrease in conductance due to destabilization of the π-system by metalThe creation of molecular components for use as electronic devices has made enormous progress. In order to advance the field further toward realistic electronic concepts, methods for the controlled modification of the conducting properties of the molecules contacted by metallic electrodes need to be further developed. Here a comprehensive study of charge transport in a class of molecules that allows modifications by introducing metal centers into organic structures is presented. Single molecules are electrically contacted and characterized in order to understand the role of the metal centers in the conductance mechanism through the molecular junctions. It is shown that the presence of single metal ions modifies the energy levels and the coupling of the molecules to the electrical contacts, and that these modifications lead to systematic variations in the statistical behavior of transport properties of the molecular junctions. A rigorous statistical analysis of thousands of junctions is performed to reveal this correlation. The understanding of the role of the metal ion in the resulting conductance properties is an essential step toward the development of molecular electronic circuits.

It is shown that double‐stranded DNA which is directly coupled to gold via a modified thymidine base exhibits a higher conductance than reported for DNA coupled to metal electrodes using different binding schemes. The measurements of electrical conductance are performed in a mechanically controlled break junction setup in aqueous solution and in high vacuum at room temperature. The current–voltage characteristics obtained in vacuum can be understood if a single molecular energy level determines the transport.

Molecular electronics aims at using single molecules as active and passive circuit elements. For the development of real electrical circuits, the operation of such molecules in contact to conducting electrodes needs to be demonstrated reliably. In article number 1500017, A. Erbe and co‐workers demonstrate a single molecule switch, the conductance of which can increase by several orders of magnitude when illuminated by light.