Light‐Induced Switching of Tunable Single‐Molecule Junctions

Abstract

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.

Enlightening Materials with Photoswitches

“…The observed effect was attributed to the fact that the frontier molecular orbitals are energetically perfectly suited to allow for resonant tunneling through the closed but not the open isomer. The latter has also been observed for various DAEs at the single molecule level …”

Reversible Switching Phenomenon in Diarylethene Molecular Devices with Reduced Graphene Oxide Electrodes on Flexible Substrates

“…The photoswitching device has two different electrical conductance states, which are identified as the closed (high degree of π‐conjugation) state or the open (broken π‐conjugation) state . It is possible to convert from the open to the closed state by exposing the molecules to UV light (at wavelengths from 290 to 370 nm), or from the closed to the open state with visible light (at wavelengths from 450 to 630 nm) . For the SAM deposition process, we prepared a diluted solution of the molecules (≈3 × 10 −3 m ) in ethanol and added a small amount of ammonium hydroxide (NH 4 OH) to the molecular solution in order to deprotect the thiol end‐group from the acetyl (COCH 3 ), so that the thiol end‐group enables good electrical contact to the Au electrodes by thiol–Au chemisorption .…”

“…By employing poly‐(3,4‐ethylenedioxythiophene) stabilized with a poly‐(4‐styrenesulfonic acid) (PEDOT:PSS) interlayer in the molecular devices, we have previously demonstrated high device yield and reliable initialization of the photostate in molecular devices of the diarylethene class on flexible substrates . The diarylethene photoswitching molecular devices have shown two stable electrical states; a closed (high conductance) state or an open (low conductance) state are created upon illumination with UV or visible light, respectively . However, these two conductance states were defined and fixed during the device fabrication with illumination of either UV or visible light and the devices failed to show the reversible switching phenomenon .…”

Nano-fabrication of molecular electronic junctions by targeted modification of metal-molecule bonds

“…Electronic structure and conductance of a single molecule can be determined experimentally by techniques34, such as scanning tunneling microscope break-junction (STM-BJ)56, conductive atomic force microscopy7 and mechanically controlled break-junctions (MCBJ)89. The electrical properties of molecular assemblies can also be measured through formation of self-assembled monolayers on metallic substrate which provides the back-contact and where the top contact has been made either by using liquid metal electrode10 or by depositing metal on top of insulating nanopores with molecules11 or by cross bar structure12.…”