Ensuring homology between 2D and 3D molecular crystals.

Integrated studies using scanning tunneling microscopy and X-ray crystallography have established that 4,5,9,10-tetrahydropyrene-2,7-dicarboxylic acid and pyrene-2,7-dicarboxylic acid crystallize in 2D and 3D with striking homology. Different behavior is shown by related biphenyls that lack the planarizing conformational constraints of the pyrenyl core and the directing effects of intermolecular hydrogen bonding. The results of these studies show that molecules specifically designed to engage in multiple strong directional interadsorbate interactions are promising tools for imposing particular nanopatterns on surfaces and for revealing subtle aspects of crystallization.