Synthesis, electronic properties and on-surface switching behaviour of triazatruxene dimers and tetramers

Abstract

The realization of single molecule-based electronic switching devices is an intriguing perspective on the path towards ultimate device miniaturization. In particular, the integration of multiple switching centers into a single molecule will open new possibilities for device integration. Here, we report on the synthesis, characterization, and the redox and the on-surface switching properties of the triazatruxene (TAT) dimer 1 and tetramer 2 with covalent butadiynediyl or ethynediyl linkages between the TAT moieties. TAT oxidation gives rise to electronic absorption over the entire range of electromagnetic radiation in the UV/vis/NIR (NIR = near infrared), with TAT → TAT⁺ charge transfer absorptions in mixed-valent redox states. For on-surface switching, both compounds were successfully deposited on an Ag(111) substrate using electrospray deposition (ESD). Compound 1 retains the low-bias three-level switching of both constituting TAT units, giving rise to six distinguishable switching states. In tetramer 2, the larger number of substrate anchoring points restricts on-surface configurations to those with only one or two non-neighbouring low-bias activatable TAT switching units. Our findings demonstrate that it is possible to realize single-molecule multi-state switches with covalently linked TAT units and pinpoint the particular impact of the substrate on their switching dynamics.