2020-07-08, Lenyk, Bohdan, Schöps, Volker, Boneberg, Johannes, Kabdulov, Mikhail, Huhn, Thomas, Scheer, Elke, Offenhäusser, Andreas, Mayer, Dirk

Diarylethene molecules are discussed as possible optical switches, which can reversibly transition between completely conjugated (closed) and nonconjugated (open) forms with different electrical conductance and optical absorbance, by exposure to UV and visible light. However, the opening reaction exhibits, in general, much lower quantum yield than the closing process, hindering their usage in optoelectronic devices. To enhance the opening process, which is supported by visible light, we employ the plasmonic field enhancement of gold films perforated with nanoholes. We show that gold nanohole arrays reveal strong optical transmission in the visible range (~60%) and pronounced enhancement of field intensities, resulting in around 50% faster switching kinetics of the molecular species in comparison with quartz substrates. The experimental UV-Vis measurements are verified with Finite-Difference Time-Domain simulation that confirm the obtained results. Thus, we propose gold nanohole arrays as transparent and conductive plasmonic material that accelerates visible-light-triggered chemical reactions including molecular switching.

2019-03-27, Koo, Jeongmin, Jang, Yeonsik, Martin, León, Kim, Dongku, Jeong, Hyunhak, Scheer, Elke, Kabdulov, Mikhail, Huhn, Thomas, Pauly, Fabian, Lee, Takhee

We fabricate and characterize vertical molecular junctions consisting of self-assembled monolayers (SAMs) of diarylethene (DAE) contacted by a multilayer graphene (MLG) electrode on the top and gold on the bottom. The DAE molecular junctions show two stable electrical states, a closed state (high conductance) or an open state (low conductance), which are created upon illumination with UV or visible light, respectively. For the Au-DAE-MLG junction structure, we observe that the current levels between the two conductance states are separated by two orders of magnitude. However, in a real-time measurement, we observe only unidirectional switching behavior from the open to the closed state.