Functionalized 4,4'-bipyridines: synthesis and 2D-organization on HOPG

Commercial 4,4'-bipyridine is a popular scaffold which is primarily employed as a linker in 3D self-assembled architectures such as metallo-organic frameworks or as connector in 2D networks. The introduction of alkyl substituents on the bipyridine skeleton is instrumental when 4,4'-bipyridines are used as linkers to form 2D self-assembled patterns on surfaces. Here, various synthetic strategies to access 4,4'-bipyridines functionalized at various positions are described. These easily scalable reactions have been used to introduce a range of alkyl substituents at positions 2 and 2', or 3 and 3' and at positions 2,2' and 6,6' in the case of tetra-functionalization. Scanning tunneling microscopy studies of molecular monolayers physisorbed at the graphite-solution interface revealed different supramolecular patterns whose motifs are primarily dictated by the nature and position of the alkyl chains.