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The pursuit of methods for design and preparation of robust nanoarchitectonic systems with integrated functionality through bottom-up methodologies remains a driving force in molecular nanotechnology. Through the use of π-conjugated covalent bonds, we demonstrate a general substrate-mediated, soft solution methodology for the preparation of extended π-conjugated polymeric nanoarchitectures in low-dimensions. Based on thermodynamic control over equilibrium polymerization at the solid-liquid interface whereby aromatic building blocks spontaneously and selectively link, close-packed arrays composed of one-dimensional (1-D) aromatic polymers and two-dimensional (2-D) macromolecular frameworks have been prepared and characterized by in situ scanning tunneling microscopy. This methodology eliminates the necessity for severe conditions and sophisticated equipment common to most current fabrication techniques and imparts almost infinite possibilities for the preparation of robust materials with designer molecular architectures.

The structures and dynamic formation processes of adlayers of 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphine (TMPyP) on both bare Au(111) and iodine-modified Au(111) in perchloric acid have been investigated in detail by using in situ scanning tunneling microscopy (STM). Highly-ordered TMPyP arrays formed on iodine-modified Au(111), whereas disordered adlayers were consistently found on bare Au(111) surface. High-resolution STM images revealed the characteristic internal shape and orientation of each TMPyP molecule in ordered adlayers. Time-dependent in situ STM allowed direct observation of the dynamics of the self-ordering processes. Before the most stable adlayer was established in a relatively small domain, several structural changes were found to occur, including the formation of a one-dimensional ordered chain at an early stage and several phase transitions in the ordered adlayers. Once the most stable adlayer was formed as a nucleus in a domain, two-dimensional growth of the domain extended over the entire area of the terraces with the final packing arrangement.

The iodine-modified Ag(111) substrate was employed as an electrode to investigate the adsorption of 5,10,-15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphine tetrakis(p-toluenesulfonate) (TMPyP) in an alkaline solution containing KI. It was found by using in situ scanning tunneling microscopy (STM) that water soluble TMPyP molecules were irreversibly adsorbed and formed highly ordered molecular adlayers on the surface of the iodine-modified Ag(111) electrode within the potential range of -0.35 to -0.10 V vs Ag/AgI. STM images revealed the characterstic shape, internal molecular structure, and molecular orientation of each TMPyP molecule in ordered adlayers. The ordered TMPyP adlayer usually consisted of stripes of several straight molecular rows with different orientations along the 3 direction of the underlying iodine adlayers. In each row, molecules were aligned with the same orientation. From the time-dependent imaging, the ordered molecular adlayer was found to grow in the specific 3 direction with an averaged growth rate of ca. 6 nm/s.

A two-dimensional molecular network of trimesic acid on Au(111) was visualized by in situ scanning tunneling microscopy with submolecular resolution. The supramolecular structures including an 'order to order' phase transition were constructed by precise potential-controlled adsorption based on adsorption-induced self-organization.

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