Characterization by X-ray Photoemission Spectroscopy of the Open and Closed Forms of a Dithienylethene Switch in Thin Films

Dithienylethene-based molecular switches have been extensively studied in solution and are considered excellent candidates in the design of molecular-based electronic devices. However, for most foreseeable applications they have to be integrated in the solid state, namely as building blocks in bottom-up approaches to prepare functional and addressable surfaces. Here we present a study of the electronic structure and chemical nature of dithienylethene switch thin films on Au(111) by X-ray photoemission spectroscopy, which proves to be a powerful technique to distinguish between the “open” and “closed” forms of the switch and gives information on the interactions between molecules and substrate. We explored the switching behavior of thin films when irradiated with UV and visible light. It is demonstrated that, despite the quenching effect that can be induced by the metal substrate, dithienylethenes can reversibly switch from open to closed form in thin solid films deposited on metal surfaces. We also showed that illumination of the closed form of dithienylethene with visible light induces not only the switching process in molecules isolated from the metal surface but also chemisorption of dithienylethene molecules that are in contact with Au(111). These results provide rationalization of the phenomena that take place while switching dithienylethenes at metal surfaces.