From graphite molecules to columnar superstructures -: an exercise in nanoscience

Recent advances in the field of organic molecular electronics include an increasingly significant role of discotic structures based on all-benzenoid polycyclic aromatic hydrocarbons (PBAHs), reflected by the growing research activities in this field. Progress has profited largely from an iterative approach based on cooperation between synthetic organic chemists and physicists, both in academia and industry. The current paper deals with this class of compounds, describing the preparation of large, yet well-defined, nanoscale PBAH moieties, which then self-assemble to highly ordered, supramolecular arrays with advantageous electronic properties. Progressive miniaturisation leads from thin films as one-dimensional charge-transport layers, to single columns as potential nanowires or data storage elements, to single molecules and nanoscale (opto)electronically active components. The use of 'large' (diameter greater than or equal to1 nm) disks ensures a columnar arrangement, which can be further modified by peripheral substitution to encode bulk 3-dimensional packing, orientation at interfaces, thermal properties, and processability. Adaptation of processing techniques from solution, melt or the vapour phase plays a crucial role for the (supra)molecular arrangement, which can be controlled from the macroscopic down to the nanometre scale. Finally, the characteristics of each new material can be evaluated in terms of supramolecular order, electronic device performance, single molecule properties, etc. This paper gives a brief overview of synthetic methods and molecular design, followed by evaluation of their columnar structures over various length scales down to nanoscale, processing techniques, and device performance/electrical characterisation.