The Side Chain Makes the Difference: Investigation of the 2D Self-Assembly of 1,3,5-Tris[4-(4-pyridinyl)phenyl]benzene Derivatives by Scanning Tunneling Microscopy
D. Trawny, L. Vandromme, J. P. Rabe, H.-U. Reissig – 2014
Flexible and straightforward syntheses of a series of D3h- or C3h-symmetrical star-shaped compounds with pyridine end groups are reported. In all cases, the acid-mediated cyclocondensations of the corresponding aryl methyl ketone provided the central benzene ring. For the preceding preparation of the functionalized compound arms, Suzuki couplings were applied. The crucial introduction of the pyridine C-2 and C-6 substituents occurred by Fe(acac)3-catalyzed alkylations (acac = acetylacetonate). The preparation of the C3-symmetrical compound involved an alternating sequence of halogenations and coupling reactions. The self-assembly behavior of the four resulting star-shaped compounds at the interface between 1-phenyloctane and the basal plane of highly oriented pyrolytic graphite (HOPG) was studied by scanning tunnelling microscopy (STM). We found self-assembled monolayers with structures strongly dependent on the substitution patterns of the investigated compounds. The reduction of the symmetry from a D3h- to a C3h-symmetrical compound led to an entirely different self-assembly behavior with the change from a hexagonal to a lamellar arrangement.