Non-Covalent Free-Standing Monolayer Nanoarchitectonics of Heterocoronene-Based Discotic Liquid Crystal Molecules

Withexcellent charge carrier mobility, tendency to form long-rangeassembly with self-healing ability, and remarkable chemical and mechanicalstability, highly conjugated discotic molecules constitute an importantclass of materials for electronic applications. Here, we report formationof the stable free-standing molecular film of heterocoronene-baseddiscotic liquid crystal (DLC) molecules, held solely by supra-molecularnon-covalent interactions. The films of monolayer thickness (similar to 4nm) were lifted from Langmuir trough directly onto a circular ringof diameter up to 2 mm as well as onto TEM grids. Films remain free-standingup to a macroscopic length scale, as revealed by optical and secondaryelectron microscopy, presumably due to the synergistic effect of intermolecular pi-pi interactions and the dispersion forces betweenthe peripheral alkyl chains as well as their interdigitation. Themonolayer is more than 97% transparent in the visible range. Further,resistive switching measurements carried out on the monolayer DLCfilm transferred on a silver substrate revealed electrochemical metallizationto be the governing process. The switching time was found to decreaseexponentially with voltage indicating nucleation to be a possiblerate-limiting step. We anticipate that the method presented here willfacilitate utilization of such non-covalent free-standing films inflexible memristor and nano-electromechanical systems.