Triazatrinaphthylene, a three-fold symmetry planar conjugated system with two-dimensional self-assembly properties

Abstract

A novel threefold symmetry planar system based on a π-conjugated triazatrinaphthylene core has been synthesized and deposited on atomically flat surfaces of highly oriented pyrolytic graphite (HOPG). Scanning tunnelling microscopy (STM) of 2,8,14-trimethyl-5,11,17-triazatrinaphthylene (denoted TrisK by analogy with the Triskele Celtic symbol) deposited at the n-tetradecane/HOPG interface reveals the spontaneous formation of self-assembled monolayers with a hexagonal close-packed arrangement extending over several tens of nanometers. Surprisingly, sub-molecular STM resolution reveals an extremely bright contrast spot on one of the three symmetrical branches of the triangular-shaped molecule TrisK. This non-equivalent adsorption site can be interpreted as originating from a local specific molecule–HOPG interaction. Besides, ab-initio calculations show that a purely molecular contribution may also be involved.