The control of spatial arrangements of molecular building blocks on surface opens the foundational step of the bottom-up approach toward future nanotechnologies. The domain size of monolayers exhibiting crystallinity generally falls in the submicron scale. Reported herein are two methods that conveniently prepare aligned discotic compounds by shear flow and patterns by electrical pulses. For the first one, polyaromatics and rod-shaped oligomers can be aligned for as long as ~7 mm, simply by placing a piece of folded tissue against the substrate to draw a shear flow of the deposition solution. The preparation scheme is similar to the Couette flow where the laminar flow takes place between two concentric walls, one of which rotates and creates viscous drag proven useful to align macromolecules. The method can induce an edge-on orientation for alkyl-decorated polyaromatics and unsubstituted coronene which would otherwise adopt the face-on arrangement on graphite. For the method of electric stimuli which can be readily delivered by an STM tip, electrical pulses (3~5 V/10 ms) make accessible the structural transformation of the molecular assembly in a controllable manner. The model compound is an alkoxylated discotic nematogen. Upon the stimuli of 3, 4, and 5 V, the assembled patterns become hexagonal, bilayer, and nanoporous, respectively. This phenomenon is attributed to the deposition of tip-induced polarized molecules to the oppositely charged substrate whose local charge redistributes upon activating the stimuli.

Monolayer assembly of polyaromatics by shear-induced alignment and by 2D porous networks

253rd National Meeting (2017)

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