Reversible conductance and surface polarity switching with synthetic molecular switches

Abstract

In recent years, the self-assembly of organic molecules has been employed to create complex smart materials. The self-assembly of smart organic molecules, such as molecular machines, could be a feasible bottom-up approach to build a variety of electronic devices. Spiropyran based molecular switches play a key role in the development of photo-responsive smart materials. However, despite research for over a hundred years in the literature on spiropyrans and related compounds, the development of functional electronic devices is still a challenge. The key issue with such functional molecules is to translate the changes that occur in a single molecule to the macroscopic world so that we can experience the result and put it to use. In this thesis, the proof of principle was demonstrated through the development and characterization of self-assembled monolayers of spiropyran and azobenzene based molecular switches. The structure of these molecules and the mechanism of their switching behavior was studied by Photo-electron spectroscopy, and water contact angle measurements. The electronic properties of the spiropyran SAMs were measured in molecular tunneling junctions comprising Eutectic Gallium-Indium as top contact. We optimized the photo-switchable conductivity by using the co-adsorption of different molecules with spiropyran on the surface. Afterwards, the optimized systems were used for the development of a proof-of-concept non-volatile memory device, where we could successfully write and erase information on the surface by using acid and base. At the end of the thesis, we also demonstrate the photo-switchable wettability of a gold surface by using host-guest chemistry.