Molecular photoswitches toward single-molecule electronics applications

Doctoral thesis, 2023

The drive towards miniaturization of electronic devices has sparked a growing interest in finding alternatives to conventional silicon-based technology. Over the years, molecular electronics has emerged as a promising avenue for the fabrication of electronic components with advanced functions. Incorporating organic molecules into electronic devices provides a new pathway to fabricate a wide range of devices with tailor-made properties. However, controlling the molecule-electrode interface in the junctions has been challenging. In this thesis, a series of photoswitches featuring the Norbornadiene-Quadricyclane (NBD-QC) systems have been studied for molecular electronics applications. NBDs terminated with various anchoring groups are synthesized, characterized and their properties for formation of reliable and reproducible junctions are investigated. The NBDs with thiol-substituted anchoring groups showed an improvement in the conductance values through the gold electrode | NBD | gold electrode junctions. The conductance of the molecular systems was investigated by using mechanically controllable break junction (MCBJ) and combined Raman / scanning tunnelling microscope break junction (STM-BJ) technique. Furthermore, a family of NBDs with amine-substituted anchoring groups was investigated for their switching properties in mCNT | NBD | mCNT (metallic carbon nanotubes) nanojunctions. The NBDs substituted with pyrene anchoring groups were found to be potential candidates for the formation of stable junctions with 2D materials such as graphene electrodes. Beyond NBD, this thesis also investigates the potential of azobenzene derivatives as efficient solid-state photoswitches with red-shifted action spectra via triplet-sensitization for low energy excitations to avoid heating effects in optoelectronics. Overall, this thesis reveals the molecular and optical properties of photoswitches and provides insight into how to apply these molecular systems in molecular electronics.